gopkg.in/yaml.v3/scannerc.go

//
// Copyright (c) 2011-2019 Canonical Ltd
// Copyright (c) 2006-2010 Kirill Simonov
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in
// the Software without restriction, including without limitation the rights to
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
// of the Software, and to permit persons to whom the Software is furnished to do
// so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package yaml

import (
        "bytes"
        "fmt"
)

// Introduction
// ************
//
// The following notes assume that you are familiar with the YAML specification
// (http://yaml.org/spec/1.2/spec.html).  We mostly follow it, although in
// some cases we are less restrictive that it requires.
//
// The process of transforming a YAML stream into a sequence of events is
// divided on two steps: Scanning and Parsing.
//
// The Scanner transforms the input stream into a sequence of tokens, while the
// parser transform the sequence of tokens produced by the Scanner into a
// sequence of parsing events.
//
// The Scanner is rather clever and complicated. The Parser, on the contrary,
// is a straightforward implementation of a recursive-descendant parser (or,
// LL(1) parser, as it is usually called).
//
// Actually there are two issues of Scanning that might be called "clever", the
// rest is quite straightforward.  The issues are "block collection start" and
// "simple keys".  Both issues are explained below in details.
//
// Here the Scanning step is explained and implemented.  We start with the list
// of all the tokens produced by the Scanner together with short descriptions.
//
// Now, tokens:
//
//      STREAM-START(encoding)          # The stream start.
//      STREAM-END                      # The stream end.
//      VERSION-DIRECTIVE(major,minor)  # The '%YAML' directive.
//      TAG-DIRECTIVE(handle,prefix)    # The '%TAG' directive.
//      DOCUMENT-START                  # '---'
//      DOCUMENT-END                    # '...'
//      BLOCK-SEQUENCE-START            # Indentation increase denoting a block
//      BLOCK-MAPPING-START             # sequence or a block mapping.
//      BLOCK-END                       # Indentation decrease.
//      FLOW-SEQUENCE-START             # '['
//      FLOW-SEQUENCE-END               # ']'
//      BLOCK-SEQUENCE-START            # '{'
//      BLOCK-SEQUENCE-END              # '}'
//      BLOCK-ENTRY                     # '-'
//      FLOW-ENTRY                      # ','
//      KEY                             # '?' or nothing (simple keys).
//      VALUE                           # ':'
//      ALIAS(anchor)                   # '*anchor'
//      ANCHOR(anchor)                  # '&anchor'
//      TAG(handle,suffix)              # '!handle!suffix'
//      SCALAR(value,style)             # A scalar.
//
// The following two tokens are "virtual" tokens denoting the beginning and the
// end of the stream:
//
//      STREAM-START(encoding)
//      STREAM-END
//
// We pass the information about the input stream encoding with the
// STREAM-START token.
//
// The next two tokens are responsible for tags:
//
//      VERSION-DIRECTIVE(major,minor)
//      TAG-DIRECTIVE(handle,prefix)
//
// Example:
//
//      %YAML   1.1
//      %TAG    !   !foo
//      %TAG    !yaml!  tag:yaml.org,2002:
//      ---
//
// The correspoding sequence of tokens:
//
//      STREAM-START(utf-8)
//      VERSION-DIRECTIVE(1,1)
//      TAG-DIRECTIVE("!","!foo")
//      TAG-DIRECTIVE("!yaml","tag:yaml.org,2002:")
//      DOCUMENT-START
//      STREAM-END
//
// Note that the VERSION-DIRECTIVE and TAG-DIRECTIVE tokens occupy a whole
// line.
//
// The document start and end indicators are represented by:
//
//      DOCUMENT-START
//      DOCUMENT-END
//
// Note that if a YAML stream contains an implicit document (without '---'
// and '...' indicators), no DOCUMENT-START and DOCUMENT-END tokens will be
// produced.
//
// In the following examples, we present whole documents together with the
// produced tokens.
//
//      1. An implicit document:
//
//          'a scalar'
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          SCALAR("a scalar",single-quoted)
//          STREAM-END
//
//      2. An explicit document:
//
//          ---
//          'a scalar'
//          ...
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          DOCUMENT-START
//          SCALAR("a scalar",single-quoted)
//          DOCUMENT-END
//          STREAM-END
//
//      3. Several documents in a stream:
//
//          'a scalar'
//          ---
//          'another scalar'
//          ---
//          'yet another scalar'
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          SCALAR("a scalar",single-quoted)
//          DOCUMENT-START
//          SCALAR("another scalar",single-quoted)
//          DOCUMENT-START
//          SCALAR("yet another scalar",single-quoted)
//          STREAM-END
//
// We have already introduced the SCALAR token above.  The following tokens are
// used to describe aliases, anchors, tag, and scalars:
//
//      ALIAS(anchor)
//      ANCHOR(anchor)
//      TAG(handle,suffix)
//      SCALAR(value,style)
//
// The following series of examples illustrate the usage of these tokens:
//
//      1. A recursive sequence:
//
//          &A [ *A ]
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          ANCHOR("A")
//          FLOW-SEQUENCE-START
//          ALIAS("A")
//          FLOW-SEQUENCE-END
//          STREAM-END
//
//      2. A tagged scalar:
//
//          !!float "3.14"  # A good approximation.
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          TAG("!!","float")
//          SCALAR("3.14",double-quoted)
//          STREAM-END
//
//      3. Various scalar styles:
//
//          --- # Implicit empty plain scalars do not produce tokens.
//          --- a plain scalar
//          --- 'a single-quoted scalar'
//          --- "a double-quoted scalar"
//          --- |-
//            a literal scalar
//          --- >-
//            a folded
//            scalar
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          DOCUMENT-START
//          DOCUMENT-START
//          SCALAR("a plain scalar",plain)
//          DOCUMENT-START
//          SCALAR("a single-quoted scalar",single-quoted)
//          DOCUMENT-START
//          SCALAR("a double-quoted scalar",double-quoted)
//          DOCUMENT-START
//          SCALAR("a literal scalar",literal)
//          DOCUMENT-START
//          SCALAR("a folded scalar",folded)
//          STREAM-END
//
// Now it's time to review collection-related tokens. We will start with
// flow collections:
//
//      FLOW-SEQUENCE-START
//      FLOW-SEQUENCE-END
//      FLOW-MAPPING-START
//      FLOW-MAPPING-END
//      FLOW-ENTRY
//      KEY
//      VALUE
//
// The tokens FLOW-SEQUENCE-START, FLOW-SEQUENCE-END, FLOW-MAPPING-START, and
// FLOW-MAPPING-END represent the indicators '[', ']', '{', and '}'
// correspondingly.  FLOW-ENTRY represent the ',' indicator.  Finally the
// indicators '?' and ':', which are used for denoting mapping keys and values,
// are represented by the KEY and VALUE tokens.
//
// The following examples show flow collections:
//
//      1. A flow sequence:
//
//          [item 1, item 2, item 3]
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          FLOW-SEQUENCE-START
//          SCALAR("item 1",plain)
//          FLOW-ENTRY
//          SCALAR("item 2",plain)
//          FLOW-ENTRY
//          SCALAR("item 3",plain)
//          FLOW-SEQUENCE-END
//          STREAM-END
//
//      2. A flow mapping:
//
//          {
//              a simple key: a value,  # Note that the KEY token is produced.
//              ? a complex key: another value,
//          }
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          FLOW-MAPPING-START
//          KEY
//          SCALAR("a simple key",plain)
//          VALUE
//          SCALAR("a value",plain)
//          FLOW-ENTRY
//          KEY
//          SCALAR("a complex key",plain)
//          VALUE
//          SCALAR("another value",plain)
//          FLOW-ENTRY
//          FLOW-MAPPING-END
//          STREAM-END
//
// A simple key is a key which is not denoted by the '?' indicator.  Note that
// the Scanner still produce the KEY token whenever it encounters a simple key.
//
// For scanning block collections, the following tokens are used (note that we
// repeat KEY and VALUE here):
//
//      BLOCK-SEQUENCE-START
//      BLOCK-MAPPING-START
//      BLOCK-END
//      BLOCK-ENTRY
//      KEY
//      VALUE
//
// The tokens BLOCK-SEQUENCE-START and BLOCK-MAPPING-START denote indentation
// increase that precedes a block collection (cf. the INDENT token in Python).
// The token BLOCK-END denote indentation decrease that ends a block collection
// (cf. the DEDENT token in Python).  However YAML has some syntax pecularities
// that makes detections of these tokens more complex.
//
// The tokens BLOCK-ENTRY, KEY, and VALUE are used to represent the indicators
// '-', '?', and ':' correspondingly.
//
// The following examples show how the tokens BLOCK-SEQUENCE-START,
// BLOCK-MAPPING-START, and BLOCK-END are emitted by the Scanner:
//
//      1. Block sequences:
//
//          - item 1
//          - item 2
//          -
//            - item 3.1
//            - item 3.2
//          -
//            key 1: value 1
//            key 2: value 2
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          BLOCK-SEQUENCE-START
//          BLOCK-ENTRY
//          SCALAR("item 1",plain)
//          BLOCK-ENTRY
//          SCALAR("item 2",plain)
//          BLOCK-ENTRY
//          BLOCK-SEQUENCE-START
//          BLOCK-ENTRY
//          SCALAR("item 3.1",plain)
//          BLOCK-ENTRY
//          SCALAR("item 3.2",plain)
//          BLOCK-END
//          BLOCK-ENTRY
//          BLOCK-MAPPING-START
//          KEY
//          SCALAR("key 1",plain)
//          VALUE
//          SCALAR("value 1",plain)
//          KEY
//          SCALAR("key 2",plain)
//          VALUE
//          SCALAR("value 2",plain)
//          BLOCK-END
//          BLOCK-END
//          STREAM-END
//
//      2. Block mappings:
//
//          a simple key: a value   # The KEY token is produced here.
//          ? a complex key
//          : another value
//          a mapping:
//            key 1: value 1
//            key 2: value 2
//          a sequence:
//            - item 1
//            - item 2
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          BLOCK-MAPPING-START
//          KEY
//          SCALAR("a simple key",plain)
//          VALUE
//          SCALAR("a value",plain)
//          KEY
//          SCALAR("a complex key",plain)
//          VALUE
//          SCALAR("another value",plain)
//          KEY
//          SCALAR("a mapping",plain)
//          BLOCK-MAPPING-START
//          KEY
//          SCALAR("key 1",plain)
//          VALUE
//          SCALAR("value 1",plain)
//          KEY
//          SCALAR("key 2",plain)
//          VALUE
//          SCALAR("value 2",plain)
//          BLOCK-END
//          KEY
//          SCALAR("a sequence",plain)
//          VALUE
//          BLOCK-SEQUENCE-START
//          BLOCK-ENTRY
//          SCALAR("item 1",plain)
//          BLOCK-ENTRY
//          SCALAR("item 2",plain)
//          BLOCK-END
//          BLOCK-END
//          STREAM-END
//
// YAML does not always require to start a new block collection from a new
// line.  If the current line contains only '-', '?', and ':' indicators, a new
// block collection may start at the current line.  The following examples
// illustrate this case:
//
//      1. Collections in a sequence:
//
//          - - item 1
//            - item 2
//          - key 1: value 1
//            key 2: value 2
//          - ? complex key
//            : complex value
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          BLOCK-SEQUENCE-START
//          BLOCK-ENTRY
//          BLOCK-SEQUENCE-START
//          BLOCK-ENTRY
//          SCALAR("item 1",plain)
//          BLOCK-ENTRY
//          SCALAR("item 2",plain)
//          BLOCK-END
//          BLOCK-ENTRY
//          BLOCK-MAPPING-START
//          KEY
//          SCALAR("key 1",plain)
//          VALUE
//          SCALAR("value 1",plain)
//          KEY
//          SCALAR("key 2",plain)
//          VALUE
//          SCALAR("value 2",plain)
//          BLOCK-END
//          BLOCK-ENTRY
//          BLOCK-MAPPING-START
//          KEY
//          SCALAR("complex key")
//          VALUE
//          SCALAR("complex value")
//          BLOCK-END
//          BLOCK-END
//          STREAM-END
//
//      2. Collections in a mapping:
//
//          ? a sequence
//          : - item 1
//            - item 2
//          ? a mapping
//          : key 1: value 1
//            key 2: value 2
//
//      Tokens:
//
//          STREAM-START(utf-8)
//          BLOCK-MAPPING-START
//          KEY
//          SCALAR("a sequence",plain)
//          VALUE
//          BLOCK-SEQUENCE-START
//          BLOCK-ENTRY
//          SCALAR("item 1",plain)
//          BLOCK-ENTRY
//          SCALAR("item 2",plain)
//          BLOCK-END
//          KEY
//          SCALAR("a mapping",plain)
//          VALUE
//          BLOCK-MAPPING-START
//          KEY
//          SCALAR("key 1",plain)
//          VALUE
//          SCALAR("value 1",plain)
//          KEY
//          SCALAR("key 2",plain)
//          VALUE
//          SCALAR("value 2",plain)
//          BLOCK-END
//          BLOCK-END
//          STREAM-END
//
// YAML also permits non-indented sequences if they are included into a block
// mapping.  In this case, the token BLOCK-SEQUENCE-START is not produced:
//
//      key:
//      - item 1    # BLOCK-SEQUENCE-START is NOT produced here.
//      - item 2
//
// Tokens:
//
//      STREAM-START(utf-8)
//      BLOCK-MAPPING-START
//      KEY
//      SCALAR("key",plain)
//      VALUE
//      BLOCK-ENTRY
//      SCALAR("item 1",plain)
//      BLOCK-ENTRY
//      SCALAR("item 2",plain)
//      BLOCK-END
//

// Ensure that the buffer contains the required number of characters.
// Return true on success, false on failure (reader error or memory error).
func cache(parser *yaml_parser_t, length int) bool {
        // [Go] This was inlined: !cache(A, B) -> unread < B && !update(A, B)
        return parser.unread >= length || yaml_parser_update_buffer(parser, length)
}

// Advance the buffer pointer.
func skip(parser *yaml_parser_t) {
        if !is_blank(parser.buffer, parser.buffer_pos) {
                parser.newlines = 0
        }
        parser.mark.index++
        parser.mark.column++
        parser.unread--
        parser.buffer_pos += width(parser.buffer[parser.buffer_pos])
}

func skip_line(parser *yaml_parser_t) {
        if is_crlf(parser.buffer, parser.buffer_pos) {
                parser.mark.index += 2
                parser.mark.column = 0
                parser.mark.line++
                parser.unread -= 2
                parser.buffer_pos += 2
                parser.newlines++
        } else if is_break(parser.buffer, parser.buffer_pos) {
                parser.mark.index++
                parser.mark.column = 0
                parser.mark.line++
                parser.unread--
                parser.buffer_pos += width(parser.buffer[parser.buffer_pos])
                parser.newlines++
        }
}

// Copy a character to a string buffer and advance pointers.
func read(parser *yaml_parser_t, s []byte) []byte {
        if !is_blank(parser.buffer, parser.buffer_pos) {
                parser.newlines = 0
        }
        w := width(parser.buffer[parser.buffer_pos])
        if w == 0 {
                panic("invalid character sequence")
        }
        if len(s) == 0 {
                s = make([]byte, 0, 32)
        }
        if w == 1 && len(s)+w <= cap(s) {
                s = s[:len(s)+1]
                s[len(s)-1] = parser.buffer[parser.buffer_pos]
                parser.buffer_pos++
        } else {
                s = append(s, parser.buffer[parser.buffer_pos:parser.buffer_pos+w]...)
                parser.buffer_pos += w
        }
        parser.mark.index++
        parser.mark.column++
        parser.unread--
        return s
}

// Copy a line break character to a string buffer and advance pointers.
func read_line(parser *yaml_parser_t, s []byte) []byte {
        buf := parser.buffer
        pos := parser.buffer_pos
        switch {
        case buf[pos] == '\r' && buf[pos+1] == '\n':
                // CR LF . LF
                s = append(s, '\n')
                parser.buffer_pos += 2
                parser.mark.index++
                parser.unread--
        case buf[pos] == '\r' || buf[pos] == '\n':
                // CR|LF . LF
                s = append(s, '\n')
                parser.buffer_pos += 1
        case buf[pos] == '\xC2' && buf[pos+1] == '\x85':
                // NEL . LF
                s = append(s, '\n')
                parser.buffer_pos += 2
        case buf[pos] == '\xE2' && buf[pos+1] == '\x80' && (buf[pos+2] == '\xA8' || buf[pos+2] == '\xA9'):
                // LS|PS . LS|PS
                s = append(s, buf[parser.buffer_pos:pos+3]...)
                parser.buffer_pos += 3
        default:
                return s
        }
        parser.mark.index++
        parser.mark.column = 0
        parser.mark.line++
        parser.unread--
        parser.newlines++
        return s
}

// Get the next token.
func yaml_parser_scan(parser *yaml_parser_t, token *yaml_token_t) bool {
        // Erase the token object.
        *token = yaml_token_t{} // [Go] Is this necessary?

        // No tokens after STREAM-END or error.
        if parser.stream_end_produced || parser.error != yaml_NO_ERROR {
                return true
        }

        // Ensure that the tokens queue contains enough tokens.
        if !parser.token_available {
                if !yaml_parser_fetch_more_tokens(parser) {
                        return false
                }
        }

        // Fetch the next token from the queue.
        *token = parser.tokens[parser.tokens_head]
        parser.tokens_head++
        parser.tokens_parsed++
        parser.token_available = false

        if token.typ == yaml_STREAM_END_TOKEN {
                parser.stream_end_produced = true
        }
        return true
}

// Set the scanner error and return false.
func yaml_parser_set_scanner_error(parser *yaml_parser_t, context string, context_mark yaml_mark_t, problem string) bool {
        parser.error = yaml_SCANNER_ERROR
        parser.context = context
        parser.context_mark = context_mark
        parser.problem = problem
        parser.problem_mark = parser.mark
        return false
}

func yaml_parser_set_scanner_tag_error(parser *yaml_parser_t, directive bool, context_mark yaml_mark_t, problem string) bool {
        context := "while parsing a tag"
        if directive {
                context = "while parsing a %TAG directive"
        }
        return yaml_parser_set_scanner_error(parser, context, context_mark, problem)
}

func trace(args ...interface{}) func() {
        pargs := append([]interface{}{"+++"}, args...)
        fmt.Println(pargs...)
        pargs = append([]interface{}{"---"}, args...)
        return func() { fmt.Println(pargs...) }
}

// Ensure that the tokens queue contains at least one token which can be
// returned to the Parser.
func yaml_parser_fetch_more_tokens(parser *yaml_parser_t) bool {
        // While we need more tokens to fetch, do it.
        for {
                // [Go] The comment parsing logic requires a lookahead of two tokens
                // so that foot comments may be parsed in time of associating them
                // with the tokens that are parsed before them, and also for line
                // comments to be transformed into head comments in some edge cases.
                if parser.tokens_head < len(parser.tokens)-2 {
                        // If a potential simple key is at the head position, we need to fetch
                        // the next token to disambiguate it.
                        head_tok_idx, ok := parser.simple_keys_by_tok[parser.tokens_parsed]
                        if !ok {
                                break
                        } else if valid, ok := yaml_simple_key_is_valid(parser, &parser.simple_keys[head_tok_idx]); !ok {
                                return false
                        } else if !valid {
                                break
                        }
                }
                // Fetch the next token.
                if !yaml_parser_fetch_next_token(parser) {
                        return false
                }
        }

        parser.token_available = true
        return true
}

// The dispatcher for token fetchers.
func yaml_parser_fetch_next_token(parser *yaml_parser_t) (ok bool) {
        // Ensure that the buffer is initialized.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }

        // Check if we just started scanning.  Fetch STREAM-START then.
        if !parser.stream_start_produced {
                return yaml_parser_fetch_stream_start(parser)
        }

        scan_mark := parser.mark

        // Eat whitespaces and comments until we reach the next token.
        if !yaml_parser_scan_to_next_token(parser) {
                return false
        }

        // [Go] While unrolling indents, transform the head comments of prior
        // indentation levels observed after scan_start into foot comments at
        // the respective indexes.

        // Check the indentation level against the current column.
        if !yaml_parser_unroll_indent(parser, parser.mark.column, scan_mark) {
                return false
        }

        // Ensure that the buffer contains at least 4 characters.  4 is the length
        // of the longest indicators ('--- ' and '... ').
        if parser.unread < 4 && !yaml_parser_update_buffer(parser, 4) {
                return false
        }

        // Is it the end of the stream?
        if is_z(parser.buffer, parser.buffer_pos) {
                return yaml_parser_fetch_stream_end(parser)
        }

        // Is it a directive?
        if parser.mark.column == 0 && parser.buffer[parser.buffer_pos] == '%' {
                return yaml_parser_fetch_directive(parser)
        }

        buf := parser.buffer
        pos := parser.buffer_pos

        // Is it the document start indicator?
        if parser.mark.column == 0 && buf[pos] == '-' && buf[pos+1] == '-' && buf[pos+2] == '-' && is_blankz(buf, pos+3) {
                return yaml_parser_fetch_document_indicator(parser, yaml_DOCUMENT_START_TOKEN)
        }

        // Is it the document end indicator?
        if parser.mark.column == 0 && buf[pos] == '.' && buf[pos+1] == '.' && buf[pos+2] == '.' && is_blankz(buf, pos+3) {
                return yaml_parser_fetch_document_indicator(parser, yaml_DOCUMENT_END_TOKEN)
        }

        comment_mark := parser.mark
        if len(parser.tokens) > 0 && (parser.flow_level == 0 && buf[pos] == ':' || parser.flow_level > 0 && buf[pos] == ',') {
                // Associate any following comments with the prior token.
                comment_mark = parser.tokens[len(parser.tokens)-1].start_mark
        }
        defer func() {
                if !ok {
                        return
                }
                if len(parser.tokens) > 0 && parser.tokens[len(parser.tokens)-1].typ == yaml_BLOCK_ENTRY_TOKEN {
                        // Sequence indicators alone have no line comments. It becomes
                        // a head comment for whatever follows.
                        return
                }
                if !yaml_parser_scan_line_comment(parser, comment_mark) {
                        ok = false
                        return
                }
        }()

        // Is it the flow sequence start indicator?
        if buf[pos] == '[' {
                return yaml_parser_fetch_flow_collection_start(parser, yaml_FLOW_SEQUENCE_START_TOKEN)
        }

        // Is it the flow mapping start indicator?
        if parser.buffer[parser.buffer_pos] == '{' {
                return yaml_parser_fetch_flow_collection_start(parser, yaml_FLOW_MAPPING_START_TOKEN)
        }

        // Is it the flow sequence end indicator?
        if parser.buffer[parser.buffer_pos] == ']' {
                return yaml_parser_fetch_flow_collection_end(parser,
                        yaml_FLOW_SEQUENCE_END_TOKEN)
        }

        // Is it the flow mapping end indicator?
        if parser.buffer[parser.buffer_pos] == '}' {
                return yaml_parser_fetch_flow_collection_end(parser,
                        yaml_FLOW_MAPPING_END_TOKEN)
        }

        // Is it the flow entry indicator?
        if parser.buffer[parser.buffer_pos] == ',' {
                return yaml_parser_fetch_flow_entry(parser)
        }

        // Is it the block entry indicator?
        if parser.buffer[parser.buffer_pos] == '-' && is_blankz(parser.buffer, parser.buffer_pos+1) {
                return yaml_parser_fetch_block_entry(parser)
        }

        // Is it the key indicator?
        if parser.buffer[parser.buffer_pos] == '?' && (parser.flow_level > 0 || is_blankz(parser.buffer, parser.buffer_pos+1)) {
                return yaml_parser_fetch_key(parser)
        }

        // Is it the value indicator?
        if parser.buffer[parser.buffer_pos] == ':' && (parser.flow_level > 0 || is_blankz(parser.buffer, parser.buffer_pos+1)) {
                return yaml_parser_fetch_value(parser)
        }

        // Is it an alias?
        if parser.buffer[parser.buffer_pos] == '*' {
                return yaml_parser_fetch_anchor(parser, yaml_ALIAS_TOKEN)
        }

        // Is it an anchor?
        if parser.buffer[parser.buffer_pos] == '&' {
                return yaml_parser_fetch_anchor(parser, yaml_ANCHOR_TOKEN)
        }

        // Is it a tag?
        if parser.buffer[parser.buffer_pos] == '!' {
                return yaml_parser_fetch_tag(parser)
        }

        // Is it a literal scalar?
        if parser.buffer[parser.buffer_pos] == '|' && parser.flow_level == 0 {
                return yaml_parser_fetch_block_scalar(parser, true)
        }

        // Is it a folded scalar?
        if parser.buffer[parser.buffer_pos] == '>' && parser.flow_level == 0 {
                return yaml_parser_fetch_block_scalar(parser, false)
        }

        // Is it a single-quoted scalar?
        if parser.buffer[parser.buffer_pos] == '\'' {
                return yaml_parser_fetch_flow_scalar(parser, true)
        }

        // Is it a double-quoted scalar?
        if parser.buffer[parser.buffer_pos] == '"' {
                return yaml_parser_fetch_flow_scalar(parser, false)
        }

        // Is it a plain scalar?
        //
        // A plain scalar may start with any non-blank characters except
        //
        //      '-', '?', ':', ',', '[', ']', '{', '}',
        //      '#', '&', '*', '!', '|', '>', '\'', '\"',
        //      '%', '@', '`'.
        //
        // In the block context (and, for the '-' indicator, in the flow context
        // too), it may also start with the characters
        //
        //      '-', '?', ':'
        //
        // if it is followed by a non-space character.
        //
        // The last rule is more restrictive than the specification requires.
        // [Go] TODO Make this logic more reasonable.
        //switch parser.buffer[parser.buffer_pos] {
        //case '-', '?', ':', ',', '?', '-', ',', ':', ']', '[', '}', '{', '&', '#', '!', '*', '>', '|', '"', '\'', '@', '%', '-', '`':
        //}
        if !(is_blankz(parser.buffer, parser.buffer_pos) || parser.buffer[parser.buffer_pos] == '-' ||
                parser.buffer[parser.buffer_pos] == '?' || parser.buffer[parser.buffer_pos] == ':' ||
                parser.buffer[parser.buffer_pos] == ',' || parser.buffer[parser.buffer_pos] == '[' ||
                parser.buffer[parser.buffer_pos] == ']' || parser.buffer[parser.buffer_pos] == '{' ||
                parser.buffer[parser.buffer_pos] == '}' || parser.buffer[parser.buffer_pos] == '#' ||
                parser.buffer[parser.buffer_pos] == '&' || parser.buffer[parser.buffer_pos] == '*' ||
                parser.buffer[parser.buffer_pos] == '!' || parser.buffer[parser.buffer_pos] == '|' ||
                parser.buffer[parser.buffer_pos] == '>' || parser.buffer[parser.buffer_pos] == '\'' ||
                parser.buffer[parser.buffer_pos] == '"' || parser.buffer[parser.buffer_pos] == '%' ||
                parser.buffer[parser.buffer_pos] == '@' || parser.buffer[parser.buffer_pos] == '`') ||
                (parser.buffer[parser.buffer_pos] == '-' && !is_blank(parser.buffer, parser.buffer_pos+1)) ||
                (parser.flow_level == 0 &&
                        (parser.buffer[parser.buffer_pos] == '?' || parser.buffer[parser.buffer_pos] == ':') &&
                        !is_blankz(parser.buffer, parser.buffer_pos+1)) {
                return yaml_parser_fetch_plain_scalar(parser)
        }

        // If we don't determine the token type so far, it is an error.
        return yaml_parser_set_scanner_error(parser,
                "while scanning for the next token", parser.mark,
                "found character that cannot start any token")
}

func yaml_simple_key_is_valid(parser *yaml_parser_t, simple_key *yaml_simple_key_t) (valid, ok bool) {
        if !simple_key.possible {
                return false, true
        }

        // The 1.2 specification says:
        //
        //     "If the ? indicator is omitted, parsing needs to see past the
        //     implicit key to recognize it as such. To limit the amount of
        //     lookahead required, the “:” indicator must appear at most 1024
        //     Unicode characters beyond the start of the key. In addition, the key
        //     is restricted to a single line."
        //
        if simple_key.mark.line < parser.mark.line || simple_key.mark.index+1024 < parser.mark.index {
                // Check if the potential simple key to be removed is required.
                if simple_key.required {
                        return false, yaml_parser_set_scanner_error(parser,
                                "while scanning a simple key", simple_key.mark,
                                "could not find expected ':'")
                }
                simple_key.possible = false
                return false, true
        }
        return true, true
}

// Check if a simple key may start at the current position and add it if
// needed.
func yaml_parser_save_simple_key(parser *yaml_parser_t) bool {
        // A simple key is required at the current position if the scanner is in
        // the block context and the current column coincides with the indentation
        // level.

        required := parser.flow_level == 0 && parser.indent == parser.mark.column

        //
        // If the current position may start a simple key, save it.
        //
        if parser.simple_key_allowed {
                simple_key := yaml_simple_key_t{
                        possible:     true,
                        required:     required,
                        token_number: parser.tokens_parsed + (len(parser.tokens) - parser.tokens_head),
                        mark:         parser.mark,
                }

                if !yaml_parser_remove_simple_key(parser) {
                        return false
                }
                parser.simple_keys[len(parser.simple_keys)-1] = simple_key
                parser.simple_keys_by_tok[simple_key.token_number] = len(parser.simple_keys) - 1
        }
        return true
}

// Remove a potential simple key at the current flow level.
func yaml_parser_remove_simple_key(parser *yaml_parser_t) bool {
        i := len(parser.simple_keys) - 1
        if parser.simple_keys[i].possible {
                // If the key is required, it is an error.
                if parser.simple_keys[i].required {
                        return yaml_parser_set_scanner_error(parser,
                                "while scanning a simple key", parser.simple_keys[i].mark,
                                "could not find expected ':'")
                }
                // Remove the key from the stack.
                parser.simple_keys[i].possible = false
                delete(parser.simple_keys_by_tok, parser.simple_keys[i].token_number)
        }
        return true
}

// max_flow_level limits the flow_level
const max_flow_level = 10000

// Increase the flow level and resize the simple key list if needed.
func yaml_parser_increase_flow_level(parser *yaml_parser_t) bool {
        // Reset the simple key on the next level.
        parser.simple_keys = append(parser.simple_keys, yaml_simple_key_t{
                possible:     false,
                required:     false,
                token_number: parser.tokens_parsed + (len(parser.tokens) - parser.tokens_head),
                mark:         parser.mark,
        })

        // Increase the flow level.
        parser.flow_level++
        if parser.flow_level > max_flow_level {
                return yaml_parser_set_scanner_error(parser,
                        "while increasing flow level", parser.simple_keys[len(parser.simple_keys)-1].mark,
                        fmt.Sprintf("exceeded max depth of %d", max_flow_level))
        }
        return true
}

// Decrease the flow level.
func yaml_parser_decrease_flow_level(parser *yaml_parser_t) bool {
        if parser.flow_level > 0 {
                parser.flow_level--
                last := len(parser.simple_keys) - 1
                delete(parser.simple_keys_by_tok, parser.simple_keys[last].token_number)
                parser.simple_keys = parser.simple_keys[:last]
        }
        return true
}

// max_indents limits the indents stack size
const max_indents = 10000

// Push the current indentation level to the stack and set the new level
// the current column is greater than the indentation level.  In this case,
// append or insert the specified token into the token queue.
func yaml_parser_roll_indent(parser *yaml_parser_t, column, number int, typ yaml_token_type_t, mark yaml_mark_t) bool {
        // In the flow context, do nothing.
        if parser.flow_level > 0 {
                return true
        }

        if parser.indent < column {
                // Push the current indentation level to the stack and set the new
                // indentation level.
                parser.indents = append(parser.indents, parser.indent)
                parser.indent = column
                if len(parser.indents) > max_indents {
                        return yaml_parser_set_scanner_error(parser,
                                "while increasing indent level", parser.simple_keys[len(parser.simple_keys)-1].mark,
                                fmt.Sprintf("exceeded max depth of %d", max_indents))
                }

                // Create a token and insert it into the queue.
                token := yaml_token_t{
                        typ:        typ,
                        start_mark: mark,
                        end_mark:   mark,
                }
                if number > -1 {
                        number -= parser.tokens_parsed
                }
                yaml_insert_token(parser, number, &token)
        }
        return true
}

// Pop indentation levels from the indents stack until the current level
// becomes less or equal to the column.  For each indentation level, append
// the BLOCK-END token.
func yaml_parser_unroll_indent(parser *yaml_parser_t, column int, scan_mark yaml_mark_t) bool {
        // In the flow context, do nothing.
        if parser.flow_level > 0 {
                return true
        }

        block_mark := scan_mark
        block_mark.index--

        // Loop through the indentation levels in the stack.
        for parser.indent > column {

                // [Go] Reposition the end token before potential following
                //      foot comments of parent blocks. For that, search
                //      backwards for recent comments that were at the same
                //      indent as the block that is ending now.
                stop_index := block_mark.index
                for i := len(parser.comments) - 1; i >= 0; i-- {
                        comment := &parser.comments[i]

                        if comment.end_mark.index < stop_index {
                                // Don't go back beyond the start of the comment/whitespace scan, unless column < 0.
                                // If requested indent column is < 0, then the document is over and everything else
                                // is a foot anyway.
                                break
                        }
                        if comment.start_mark.column == parser.indent+1 {
                                // This is a good match. But maybe there's a former comment
                                // at that same indent level, so keep searching.
                                block_mark = comment.start_mark
                        }

                        // While the end of the former comment matches with
                        // the start of the following one, we know there's
                        // nothing in between and scanning is still safe.
                        stop_index = comment.scan_mark.index
                }

                // Create a token and append it to the queue.
                token := yaml_token_t{
                        typ:        yaml_BLOCK_END_TOKEN,
                        start_mark: block_mark,
                        end_mark:   block_mark,
                }
                yaml_insert_token(parser, -1, &token)

                // Pop the indentation level.
                parser.indent = parser.indents[len(parser.indents)-1]
                parser.indents = parser.indents[:len(parser.indents)-1]
        }
        return true
}

// Initialize the scanner and produce the STREAM-START token.
func yaml_parser_fetch_stream_start(parser *yaml_parser_t) bool {

        // Set the initial indentation.
        parser.indent = -1

        // Initialize the simple key stack.
        parser.simple_keys = append(parser.simple_keys, yaml_simple_key_t{})

        parser.simple_keys_by_tok = make(map[int]int)

        // A simple key is allowed at the beginning of the stream.
        parser.simple_key_allowed = true

        // We have started.
        parser.stream_start_produced = true

        // Create the STREAM-START token and append it to the queue.
        token := yaml_token_t{
                typ:        yaml_STREAM_START_TOKEN,
                start_mark: parser.mark,
                end_mark:   parser.mark,
                encoding:   parser.encoding,
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the STREAM-END token and shut down the scanner.
func yaml_parser_fetch_stream_end(parser *yaml_parser_t) bool {

        // Force new line.
        if parser.mark.column != 0 {
                parser.mark.column = 0
                parser.mark.line++
        }

        // Reset the indentation level.
        if !yaml_parser_unroll_indent(parser, -1, parser.mark) {
                return false
        }

        // Reset simple keys.
        if !yaml_parser_remove_simple_key(parser) {
                return false
        }

        parser.simple_key_allowed = false

        // Create the STREAM-END token and append it to the queue.
        token := yaml_token_t{
                typ:        yaml_STREAM_END_TOKEN,
                start_mark: parser.mark,
                end_mark:   parser.mark,
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce a VERSION-DIRECTIVE or TAG-DIRECTIVE token.
func yaml_parser_fetch_directive(parser *yaml_parser_t) bool {
        // Reset the indentation level.
        if !yaml_parser_unroll_indent(parser, -1, parser.mark) {
                return false
        }

        // Reset simple keys.
        if !yaml_parser_remove_simple_key(parser) {
                return false
        }

        parser.simple_key_allowed = false

        // Create the YAML-DIRECTIVE or TAG-DIRECTIVE token.
        token := yaml_token_t{}
        if !yaml_parser_scan_directive(parser, &token) {
                return false
        }
        // Append the token to the queue.
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the DOCUMENT-START or DOCUMENT-END token.
func yaml_parser_fetch_document_indicator(parser *yaml_parser_t, typ yaml_token_type_t) bool {
        // Reset the indentation level.
        if !yaml_parser_unroll_indent(parser, -1, parser.mark) {
                return false
        }

        // Reset simple keys.
        if !yaml_parser_remove_simple_key(parser) {
                return false
        }

        parser.simple_key_allowed = false

        // Consume the token.
        start_mark := parser.mark

        skip(parser)
        skip(parser)
        skip(parser)

        end_mark := parser.mark

        // Create the DOCUMENT-START or DOCUMENT-END token.
        token := yaml_token_t{
                typ:        typ,
                start_mark: start_mark,
                end_mark:   end_mark,
        }
        // Append the token to the queue.
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the FLOW-SEQUENCE-START or FLOW-MAPPING-START token.
func yaml_parser_fetch_flow_collection_start(parser *yaml_parser_t, typ yaml_token_type_t) bool {

        // The indicators '[' and '{' may start a simple key.
        if !yaml_parser_save_simple_key(parser) {
                return false
        }

        // Increase the flow level.
        if !yaml_parser_increase_flow_level(parser) {
                return false
        }

        // A simple key may follow the indicators '[' and '{'.
        parser.simple_key_allowed = true

        // Consume the token.
        start_mark := parser.mark
        skip(parser)
        end_mark := parser.mark

        // Create the FLOW-SEQUENCE-START of FLOW-MAPPING-START token.
        token := yaml_token_t{
                typ:        typ,
                start_mark: start_mark,
                end_mark:   end_mark,
        }
        // Append the token to the queue.
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the FLOW-SEQUENCE-END or FLOW-MAPPING-END token.
func yaml_parser_fetch_flow_collection_end(parser *yaml_parser_t, typ yaml_token_type_t) bool {
        // Reset any potential simple key on the current flow level.
        if !yaml_parser_remove_simple_key(parser) {
                return false
        }

        // Decrease the flow level.
        if !yaml_parser_decrease_flow_level(parser) {
                return false
        }

        // No simple keys after the indicators ']' and '}'.
        parser.simple_key_allowed = false

        // Consume the token.

        start_mark := parser.mark
        skip(parser)
        end_mark := parser.mark

        // Create the FLOW-SEQUENCE-END of FLOW-MAPPING-END token.
        token := yaml_token_t{
                typ:        typ,
                start_mark: start_mark,
                end_mark:   end_mark,
        }
        // Append the token to the queue.
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the FLOW-ENTRY token.
func yaml_parser_fetch_flow_entry(parser *yaml_parser_t) bool {
        // Reset any potential simple keys on the current flow level.
        if !yaml_parser_remove_simple_key(parser) {
                return false
        }

        // Simple keys are allowed after ','.
        parser.simple_key_allowed = true

        // Consume the token.
        start_mark := parser.mark
        skip(parser)
        end_mark := parser.mark

        // Create the FLOW-ENTRY token and append it to the queue.
        token := yaml_token_t{
                typ:        yaml_FLOW_ENTRY_TOKEN,
                start_mark: start_mark,
                end_mark:   end_mark,
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the BLOCK-ENTRY token.
func yaml_parser_fetch_block_entry(parser *yaml_parser_t) bool {
        // Check if the scanner is in the block context.
        if parser.flow_level == 0 {
                // Check if we are allowed to start a new entry.
                if !parser.simple_key_allowed {
                        return yaml_parser_set_scanner_error(parser, "", parser.mark,
                                "block sequence entries are not allowed in this context")
                }
                // Add the BLOCK-SEQUENCE-START token if needed.
                if !yaml_parser_roll_indent(parser, parser.mark.column, -1, yaml_BLOCK_SEQUENCE_START_TOKEN, parser.mark) {
                        return false
                }
        } else {
                // It is an error for the '-' indicator to occur in the flow context,
                // but we let the Parser detect and report about it because the Parser
                // is able to point to the context.
        }

        // Reset any potential simple keys on the current flow level.
        if !yaml_parser_remove_simple_key(parser) {
                return false
        }

        // Simple keys are allowed after '-'.
        parser.simple_key_allowed = true

        // Consume the token.
        start_mark := parser.mark
        skip(parser)
        end_mark := parser.mark

        // Create the BLOCK-ENTRY token and append it to the queue.
        token := yaml_token_t{
                typ:        yaml_BLOCK_ENTRY_TOKEN,
                start_mark: start_mark,
                end_mark:   end_mark,
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the KEY token.
func yaml_parser_fetch_key(parser *yaml_parser_t) bool {

        // In the block context, additional checks are required.
        if parser.flow_level == 0 {
                // Check if we are allowed to start a new key (not nessesary simple).
                if !parser.simple_key_allowed {
                        return yaml_parser_set_scanner_error(parser, "", parser.mark,
                                "mapping keys are not allowed in this context")
                }
                // Add the BLOCK-MAPPING-START token if needed.
                if !yaml_parser_roll_indent(parser, parser.mark.column, -1, yaml_BLOCK_MAPPING_START_TOKEN, parser.mark) {
                        return false
                }
        }

        // Reset any potential simple keys on the current flow level.
        if !yaml_parser_remove_simple_key(parser) {
                return false
        }

        // Simple keys are allowed after '?' in the block context.
        parser.simple_key_allowed = parser.flow_level == 0

        // Consume the token.
        start_mark := parser.mark
        skip(parser)
        end_mark := parser.mark

        // Create the KEY token and append it to the queue.
        token := yaml_token_t{
                typ:        yaml_KEY_TOKEN,
                start_mark: start_mark,
                end_mark:   end_mark,
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the VALUE token.
func yaml_parser_fetch_value(parser *yaml_parser_t) bool {

        simple_key := &parser.simple_keys[len(parser.simple_keys)-1]

        // Have we found a simple key?
        if valid, ok := yaml_simple_key_is_valid(parser, simple_key); !ok {
                return false

        } else if valid {

                // Create the KEY token and insert it into the queue.
                token := yaml_token_t{
                        typ:        yaml_KEY_TOKEN,
                        start_mark: simple_key.mark,
                        end_mark:   simple_key.mark,
                }
                yaml_insert_token(parser, simple_key.token_number-parser.tokens_parsed, &token)

                // In the block context, we may need to add the BLOCK-MAPPING-START token.
                if !yaml_parser_roll_indent(parser, simple_key.mark.column,
                        simple_key.token_number,
                        yaml_BLOCK_MAPPING_START_TOKEN, simple_key.mark) {
                        return false
                }

                // Remove the simple key.
                simple_key.possible = false
                delete(parser.simple_keys_by_tok, simple_key.token_number)

                // A simple key cannot follow another simple key.
                parser.simple_key_allowed = false

        } else {
                // The ':' indicator follows a complex key.

                // In the block context, extra checks are required.
                if parser.flow_level == 0 {

                        // Check if we are allowed to start a complex value.
                        if !parser.simple_key_allowed {
                                return yaml_parser_set_scanner_error(parser, "", parser.mark,
                                        "mapping values are not allowed in this context")
                        }

                        // Add the BLOCK-MAPPING-START token if needed.
                        if !yaml_parser_roll_indent(parser, parser.mark.column, -1, yaml_BLOCK_MAPPING_START_TOKEN, parser.mark) {
                                return false
                        }
                }

                // Simple keys after ':' are allowed in the block context.
                parser.simple_key_allowed = parser.flow_level == 0
        }

        // Consume the token.
        start_mark := parser.mark
        skip(parser)
        end_mark := parser.mark

        // Create the VALUE token and append it to the queue.
        token := yaml_token_t{
                typ:        yaml_VALUE_TOKEN,
                start_mark: start_mark,
                end_mark:   end_mark,
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the ALIAS or ANCHOR token.
func yaml_parser_fetch_anchor(parser *yaml_parser_t, typ yaml_token_type_t) bool {
        // An anchor or an alias could be a simple key.
        if !yaml_parser_save_simple_key(parser) {
                return false
        }

        // A simple key cannot follow an anchor or an alias.
        parser.simple_key_allowed = false

        // Create the ALIAS or ANCHOR token and append it to the queue.
        var token yaml_token_t
        if !yaml_parser_scan_anchor(parser, &token, typ) {
                return false
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the TAG token.
func yaml_parser_fetch_tag(parser *yaml_parser_t) bool {
        // A tag could be a simple key.
        if !yaml_parser_save_simple_key(parser) {
                return false
        }

        // A simple key cannot follow a tag.
        parser.simple_key_allowed = false

        // Create the TAG token and append it to the queue.
        var token yaml_token_t
        if !yaml_parser_scan_tag(parser, &token) {
                return false
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the SCALAR(...,literal) or SCALAR(...,folded) tokens.
func yaml_parser_fetch_block_scalar(parser *yaml_parser_t, literal bool) bool {
        // Remove any potential simple keys.
        if !yaml_parser_remove_simple_key(parser) {
                return false
        }

        // A simple key may follow a block scalar.
        parser.simple_key_allowed = true

        // Create the SCALAR token and append it to the queue.
        var token yaml_token_t
        if !yaml_parser_scan_block_scalar(parser, &token, literal) {
                return false
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the SCALAR(...,single-quoted) or SCALAR(...,double-quoted) tokens.
func yaml_parser_fetch_flow_scalar(parser *yaml_parser_t, single bool) bool {
        // A plain scalar could be a simple key.
        if !yaml_parser_save_simple_key(parser) {
                return false
        }

        // A simple key cannot follow a flow scalar.
        parser.simple_key_allowed = false

        // Create the SCALAR token and append it to the queue.
        var token yaml_token_t
        if !yaml_parser_scan_flow_scalar(parser, &token, single) {
                return false
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Produce the SCALAR(...,plain) token.
func yaml_parser_fetch_plain_scalar(parser *yaml_parser_t) bool {
        // A plain scalar could be a simple key.
        if !yaml_parser_save_simple_key(parser) {
                return false
        }

        // A simple key cannot follow a flow scalar.
        parser.simple_key_allowed = false

        // Create the SCALAR token and append it to the queue.
        var token yaml_token_t
        if !yaml_parser_scan_plain_scalar(parser, &token) {
                return false
        }
        yaml_insert_token(parser, -1, &token)
        return true
}

// Eat whitespaces and comments until the next token is found.
func yaml_parser_scan_to_next_token(parser *yaml_parser_t) bool {

        scan_mark := parser.mark

        // Until the next token is not found.
        for {
                // Allow the BOM mark to start a line.
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
                if parser.mark.column == 0 && is_bom(parser.buffer, parser.buffer_pos) {
                        skip(parser)
                }

                // Eat whitespaces.
                // Tabs are allowed:
                //  - in the flow context
                //  - in the block context, but not at the beginning of the line or
                //  after '-', '?', or ':' (complex value).
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }

                for parser.buffer[parser.buffer_pos] == ' ' || ((parser.flow_level > 0 || !parser.simple_key_allowed) && parser.buffer[parser.buffer_pos] == '\t') {
                        skip(parser)
                        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                return false
                        }
                }

                // Check if we just had a line comment under a sequence entry that
                // looks more like a header to the following content. Similar to this:
                //
                // - # The comment
                //   - Some data
                //
                // If so, transform the line comment to a head comment and reposition.
                if len(parser.comments) > 0 && len(parser.tokens) > 1 {
                        tokenA := parser.tokens[len(parser.tokens)-2]
                        tokenB := parser.tokens[len(parser.tokens)-1]
                        comment := &parser.comments[len(parser.comments)-1]
                        if tokenA.typ == yaml_BLOCK_SEQUENCE_START_TOKEN && tokenB.typ == yaml_BLOCK_ENTRY_TOKEN && len(comment.line) > 0 && !is_break(parser.buffer, parser.buffer_pos) {
                                // If it was in the prior line, reposition so it becomes a
                                // header of the follow up token. Otherwise, keep it in place
                                // so it becomes a header of the former.
                                comment.head = comment.line
                                comment.line = nil
                                if comment.start_mark.line == parser.mark.line-1 {
                                        comment.token_mark = parser.mark
                                }
                        }
                }

                // Eat a comment until a line break.
                if parser.buffer[parser.buffer_pos] == '#' {
                        if !yaml_parser_scan_comments(parser, scan_mark) {
                                return false
                        }
                }

                // If it is a line break, eat it.
                if is_break(parser.buffer, parser.buffer_pos) {
                        if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                                return false
                        }
                        skip_line(parser)

                        // In the block context, a new line may start a simple key.
                        if parser.flow_level == 0 {
                                parser.simple_key_allowed = true
                        }
                } else {
                        break // We have found a token.
                }
        }

        return true
}

// Scan a YAML-DIRECTIVE or TAG-DIRECTIVE token.
//
// Scope:
//      %YAML    1.1    # a comment \n
//      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
//      %TAG    !yaml!  tag:yaml.org,2002:  \n
//      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
//
func yaml_parser_scan_directive(parser *yaml_parser_t, token *yaml_token_t) bool {
        // Eat '%'.
        start_mark := parser.mark
        skip(parser)

        // Scan the directive name.
        var name []byte
        if !yaml_parser_scan_directive_name(parser, start_mark, &name) {
                return false
        }

        // Is it a YAML directive?
        if bytes.Equal(name, []byte("YAML")) {
                // Scan the VERSION directive value.
                var major, minor int8
                if !yaml_parser_scan_version_directive_value(parser, start_mark, &major, &minor) {
                        return false
                }
                end_mark := parser.mark

                // Create a VERSION-DIRECTIVE token.
                *token = yaml_token_t{
                        typ:        yaml_VERSION_DIRECTIVE_TOKEN,
                        start_mark: start_mark,
                        end_mark:   end_mark,
                        major:      major,
                        minor:      minor,
                }

                // Is it a TAG directive?
        } else if bytes.Equal(name, []byte("TAG")) {
                // Scan the TAG directive value.
                var handle, prefix []byte
                if !yaml_parser_scan_tag_directive_value(parser, start_mark, &handle, &prefix) {
                        return false
                }
                end_mark := parser.mark

                // Create a TAG-DIRECTIVE token.
                *token = yaml_token_t{
                        typ:        yaml_TAG_DIRECTIVE_TOKEN,
                        start_mark: start_mark,
                        end_mark:   end_mark,
                        value:      handle,
                        prefix:     prefix,
                }

                // Unknown directive.
        } else {
                yaml_parser_set_scanner_error(parser, "while scanning a directive",
                        start_mark, "found unknown directive name")
                return false
        }

        // Eat the rest of the line including any comments.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }

        for is_blank(parser.buffer, parser.buffer_pos) {
                skip(parser)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }

        if parser.buffer[parser.buffer_pos] == '#' {
                // [Go] Discard this inline comment for the time being.
                //if !yaml_parser_scan_line_comment(parser, start_mark) {
                //      return false
                //}
                for !is_breakz(parser.buffer, parser.buffer_pos) {
                        skip(parser)
                        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                return false
                        }
                }
        }

        // Check if we are at the end of the line.
        if !is_breakz(parser.buffer, parser.buffer_pos) {
                yaml_parser_set_scanner_error(parser, "while scanning a directive",
                        start_mark, "did not find expected comment or line break")
                return false
        }

        // Eat a line break.
        if is_break(parser.buffer, parser.buffer_pos) {
                if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                        return false
                }
                skip_line(parser)
        }

        return true
}

// Scan the directive name.
//
// Scope:
//      %YAML   1.1     # a comment \n
//       ^^^^
//      %TAG    !yaml!  tag:yaml.org,2002:  \n
//       ^^^
//
func yaml_parser_scan_directive_name(parser *yaml_parser_t, start_mark yaml_mark_t, name *[]byte) bool {
        // Consume the directive name.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }

        var s []byte
        for is_alpha(parser.buffer, parser.buffer_pos) {
                s = read(parser, s)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }

        // Check if the name is empty.
        if len(s) == 0 {
                yaml_parser_set_scanner_error(parser, "while scanning a directive",
                        start_mark, "could not find expected directive name")
                return false
        }

        // Check for an blank character after the name.
        if !is_blankz(parser.buffer, parser.buffer_pos) {
                yaml_parser_set_scanner_error(parser, "while scanning a directive",
                        start_mark, "found unexpected non-alphabetical character")
                return false
        }
        *name = s
        return true
}

// Scan the value of VERSION-DIRECTIVE.
//
// Scope:
//      %YAML   1.1     # a comment \n
//           ^^^^^^
func yaml_parser_scan_version_directive_value(parser *yaml_parser_t, start_mark yaml_mark_t, major, minor *int8) bool {
        // Eat whitespaces.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        for is_blank(parser.buffer, parser.buffer_pos) {
                skip(parser)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }

        // Consume the major version number.
        if !yaml_parser_scan_version_directive_number(parser, start_mark, major) {
                return false
        }

        // Eat '.'.
        if parser.buffer[parser.buffer_pos] != '.' {
                return yaml_parser_set_scanner_error(parser, "while scanning a %YAML directive",
                        start_mark, "did not find expected digit or '.' character")
        }

        skip(parser)

        // Consume the minor version number.
        if !yaml_parser_scan_version_directive_number(parser, start_mark, minor) {
                return false
        }
        return true
}

const max_number_length = 2

// Scan the version number of VERSION-DIRECTIVE.
//
// Scope:
//      %YAML   1.1     # a comment \n
//              ^
//      %YAML   1.1     # a comment \n
//                ^
func yaml_parser_scan_version_directive_number(parser *yaml_parser_t, start_mark yaml_mark_t, number *int8) bool {

        // Repeat while the next character is digit.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        var value, length int8
        for is_digit(parser.buffer, parser.buffer_pos) {
                // Check if the number is too long.
                length++
                if length > max_number_length {
                        return yaml_parser_set_scanner_error(parser, "while scanning a %YAML directive",
                                start_mark, "found extremely long version number")
                }
                value = value*10 + int8(as_digit(parser.buffer, parser.buffer_pos))
                skip(parser)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }

        // Check if the number was present.
        if length == 0 {
                return yaml_parser_set_scanner_error(parser, "while scanning a %YAML directive",
                        start_mark, "did not find expected version number")
        }
        *number = value
        return true
}

// Scan the value of a TAG-DIRECTIVE token.
//
// Scope:
//      %TAG    !yaml!  tag:yaml.org,2002:  \n
//          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
//
func yaml_parser_scan_tag_directive_value(parser *yaml_parser_t, start_mark yaml_mark_t, handle, prefix *[]byte) bool {
        var handle_value, prefix_value []byte

        // Eat whitespaces.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }

        for is_blank(parser.buffer, parser.buffer_pos) {
                skip(parser)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }

        // Scan a handle.
        if !yaml_parser_scan_tag_handle(parser, true, start_mark, &handle_value) {
                return false
        }

        // Expect a whitespace.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        if !is_blank(parser.buffer, parser.buffer_pos) {
                yaml_parser_set_scanner_error(parser, "while scanning a %TAG directive",
                        start_mark, "did not find expected whitespace")
                return false
        }

        // Eat whitespaces.
        for is_blank(parser.buffer, parser.buffer_pos) {
                skip(parser)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }

        // Scan a prefix.
        if !yaml_parser_scan_tag_uri(parser, true, nil, start_mark, &prefix_value) {
                return false
        }

        // Expect a whitespace or line break.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        if !is_blankz(parser.buffer, parser.buffer_pos) {
                yaml_parser_set_scanner_error(parser, "while scanning a %TAG directive",
                        start_mark, "did not find expected whitespace or line break")
                return false
        }

        *handle = handle_value
        *prefix = prefix_value
        return true
}

func yaml_parser_scan_anchor(parser *yaml_parser_t, token *yaml_token_t, typ yaml_token_type_t) bool {
        var s []byte

        // Eat the indicator character.
        start_mark := parser.mark
        skip(parser)

        // Consume the value.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }

        for is_alpha(parser.buffer, parser.buffer_pos) {
                s = read(parser, s)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }

        end_mark := parser.mark

        /*
         * Check if length of the anchor is greater than 0 and it is followed by
         * a whitespace character or one of the indicators:
         *
         *      '?', ':', ',', ']', '}', '%', '@', '`'.
         */

        if len(s) == 0 ||
                !(is_blankz(parser.buffer, parser.buffer_pos) || parser.buffer[parser.buffer_pos] == '?' ||
                        parser.buffer[parser.buffer_pos] == ':' || parser.buffer[parser.buffer_pos] == ',' ||
                        parser.buffer[parser.buffer_pos] == ']' || parser.buffer[parser.buffer_pos] == '}' ||
                        parser.buffer[parser.buffer_pos] == '%' || parser.buffer[parser.buffer_pos] == '@' ||
                        parser.buffer[parser.buffer_pos] == '`') {
                context := "while scanning an alias"
                if typ == yaml_ANCHOR_TOKEN {
                        context = "while scanning an anchor"
                }
                yaml_parser_set_scanner_error(parser, context, start_mark,
                        "did not find expected alphabetic or numeric character")
                return false
        }

        // Create a token.
        *token = yaml_token_t{
                typ:        typ,
                start_mark: start_mark,
                end_mark:   end_mark,
                value:      s,
        }

        return true
}

/*
 * Scan a TAG token.
 */

func yaml_parser_scan_tag(parser *yaml_parser_t, token *yaml_token_t) bool {
        var handle, suffix []byte

        start_mark := parser.mark

        // Check if the tag is in the canonical form.
        if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                return false
        }

        if parser.buffer[parser.buffer_pos+1] == '<' {
                // Keep the handle as ''

                // Eat '!<'
                skip(parser)
                skip(parser)

                // Consume the tag value.
                if !yaml_parser_scan_tag_uri(parser, false, nil, start_mark, &suffix) {
                        return false
                }

                // Check for '>' and eat it.
                if parser.buffer[parser.buffer_pos] != '>' {
                        yaml_parser_set_scanner_error(parser, "while scanning a tag",
                                start_mark, "did not find the expected '>'")
                        return false
                }

                skip(parser)
        } else {
                // The tag has either the '!suffix' or the '!handle!suffix' form.

                // First, try to scan a handle.
                if !yaml_parser_scan_tag_handle(parser, false, start_mark, &handle) {
                        return false
                }

                // Check if it is, indeed, handle.
                if handle[0] == '!' && len(handle) > 1 && handle[len(handle)-1] == '!' {
                        // Scan the suffix now.
                        if !yaml_parser_scan_tag_uri(parser, false, nil, start_mark, &suffix) {
                                return false
                        }
                } else {
                        // It wasn't a handle after all.  Scan the rest of the tag.
                        if !yaml_parser_scan_tag_uri(parser, false, handle, start_mark, &suffix) {
                                return false
                        }

                        // Set the handle to '!'.
                        handle = []byte{'!'}

                        // A special case: the '!' tag.  Set the handle to '' and the
                        // suffix to '!'.
                        if len(suffix) == 0 {
                                handle, suffix = suffix, handle
                        }
                }
        }

        // Check the character which ends the tag.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        if !is_blankz(parser.buffer, parser.buffer_pos) {
                yaml_parser_set_scanner_error(parser, "while scanning a tag",
                        start_mark, "did not find expected whitespace or line break")
                return false
        }

        end_mark := parser.mark

        // Create a token.
        *token = yaml_token_t{
                typ:        yaml_TAG_TOKEN,
                start_mark: start_mark,
                end_mark:   end_mark,
                value:      handle,
                suffix:     suffix,
        }
        return true
}

// Scan a tag handle.
func yaml_parser_scan_tag_handle(parser *yaml_parser_t, directive bool, start_mark yaml_mark_t, handle *[]byte) bool {
        // Check the initial '!' character.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        if parser.buffer[parser.buffer_pos] != '!' {
                yaml_parser_set_scanner_tag_error(parser, directive,
                        start_mark, "did not find expected '!'")
                return false
        }

        var s []byte

        // Copy the '!' character.
        s = read(parser, s)

        // Copy all subsequent alphabetical and numerical characters.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        for is_alpha(parser.buffer, parser.buffer_pos) {
                s = read(parser, s)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }

        // Check if the trailing character is '!' and copy it.
        if parser.buffer[parser.buffer_pos] == '!' {
                s = read(parser, s)
        } else {
                // It's either the '!' tag or not really a tag handle.  If it's a %TAG
                // directive, it's an error.  If it's a tag token, it must be a part of URI.
                if directive && string(s) != "!" {
                        yaml_parser_set_scanner_tag_error(parser, directive,
                                start_mark, "did not find expected '!'")
                        return false
                }
        }

        *handle = s
        return true
}

// Scan a tag.
func yaml_parser_scan_tag_uri(parser *yaml_parser_t, directive bool, head []byte, start_mark yaml_mark_t, uri *[]byte) bool {
        //size_t length = head ? strlen((char *)head) : 0
        var s []byte
        hasTag := len(head) > 0

        // Copy the head if needed.
        //
        // Note that we don't copy the leading '!' character.
        if len(head) > 1 {
                s = append(s, head[1:]...)
        }

        // Scan the tag.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }

        // The set of characters that may appear in URI is as follows:
        //
        //      '0'-'9', 'A'-'Z', 'a'-'z', '_', '-', ';', '/', '?', ':', '@', '&',
        //      '=', '+', '$', ',', '.', '!', '~', '*', '\'', '(', ')', '[', ']',
        //      '%'.
        // [Go] TODO Convert this into more reasonable logic.
        for is_alpha(parser.buffer, parser.buffer_pos) || parser.buffer[parser.buffer_pos] == ';' ||
                parser.buffer[parser.buffer_pos] == '/' || parser.buffer[parser.buffer_pos] == '?' ||
                parser.buffer[parser.buffer_pos] == ':' || parser.buffer[parser.buffer_pos] == '@' ||
                parser.buffer[parser.buffer_pos] == '&' || parser.buffer[parser.buffer_pos] == '=' ||
                parser.buffer[parser.buffer_pos] == '+' || parser.buffer[parser.buffer_pos] == '$' ||
                parser.buffer[parser.buffer_pos] == ',' || parser.buffer[parser.buffer_pos] == '.' ||
                parser.buffer[parser.buffer_pos] == '!' || parser.buffer[parser.buffer_pos] == '~' ||
                parser.buffer[parser.buffer_pos] == '*' || parser.buffer[parser.buffer_pos] == '\'' ||
                parser.buffer[parser.buffer_pos] == '(' || parser.buffer[parser.buffer_pos] == ')' ||
                parser.buffer[parser.buffer_pos] == '[' || parser.buffer[parser.buffer_pos] == ']' ||
                parser.buffer[parser.buffer_pos] == '%' {
                // Check if it is a URI-escape sequence.
                if parser.buffer[parser.buffer_pos] == '%' {
                        if !yaml_parser_scan_uri_escapes(parser, directive, start_mark, &s) {
                                return false
                        }
                } else {
                        s = read(parser, s)
                }
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
                hasTag = true
        }

        if !hasTag {
                yaml_parser_set_scanner_tag_error(parser, directive,
                        start_mark, "did not find expected tag URI")
                return false
        }
        *uri = s
        return true
}

// Decode an URI-escape sequence corresponding to a single UTF-8 character.
func yaml_parser_scan_uri_escapes(parser *yaml_parser_t, directive bool, start_mark yaml_mark_t, s *[]byte) bool {

        // Decode the required number of characters.
        w := 1024
        for w > 0 {
                // Check for a URI-escaped octet.
                if parser.unread < 3 && !yaml_parser_update_buffer(parser, 3) {
                        return false
                }

                if !(parser.buffer[parser.buffer_pos] == '%' &&
                        is_hex(parser.buffer, parser.buffer_pos+1) &&
                        is_hex(parser.buffer, parser.buffer_pos+2)) {
                        return yaml_parser_set_scanner_tag_error(parser, directive,
                                start_mark, "did not find URI escaped octet")
                }

                // Get the octet.
                octet := byte((as_hex(parser.buffer, parser.buffer_pos+1) << 4) + as_hex(parser.buffer, parser.buffer_pos+2))

                // If it is the leading octet, determine the length of the UTF-8 sequence.
                if w == 1024 {
                        w = width(octet)
                        if w == 0 {
                                return yaml_parser_set_scanner_tag_error(parser, directive,
                                        start_mark, "found an incorrect leading UTF-8 octet")
                        }
                } else {
                        // Check if the trailing octet is correct.
                        if octet&0xC0 != 0x80 {
                                return yaml_parser_set_scanner_tag_error(parser, directive,
                                        start_mark, "found an incorrect trailing UTF-8 octet")
                        }
                }

                // Copy the octet and move the pointers.
                *s = append(*s, octet)
                skip(parser)
                skip(parser)
                skip(parser)
                w--
        }
        return true
}

// Scan a block scalar.
func yaml_parser_scan_block_scalar(parser *yaml_parser_t, token *yaml_token_t, literal bool) bool {
        // Eat the indicator '|' or '>'.
        start_mark := parser.mark
        skip(parser)

        // Scan the additional block scalar indicators.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }

        // Check for a chomping indicator.
        var chomping, increment int
        if parser.buffer[parser.buffer_pos] == '+' || parser.buffer[parser.buffer_pos] == '-' {
                // Set the chomping method and eat the indicator.
                if parser.buffer[parser.buffer_pos] == '+' {
                        chomping = +1
                } else {
                        chomping = -1
                }
                skip(parser)

                // Check for an indentation indicator.
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
                if is_digit(parser.buffer, parser.buffer_pos) {
                        // Check that the indentation is greater than 0.
                        if parser.buffer[parser.buffer_pos] == '0' {
                                yaml_parser_set_scanner_error(parser, "while scanning a block scalar",
                                        start_mark, "found an indentation indicator equal to 0")
                                return false
                        }

                        // Get the indentation level and eat the indicator.
                        increment = as_digit(parser.buffer, parser.buffer_pos)
                        skip(parser)
                }

        } else if is_digit(parser.buffer, parser.buffer_pos) {
                // Do the same as above, but in the opposite order.

                if parser.buffer[parser.buffer_pos] == '0' {
                        yaml_parser_set_scanner_error(parser, "while scanning a block scalar",
                                start_mark, "found an indentation indicator equal to 0")
                        return false
                }
                increment = as_digit(parser.buffer, parser.buffer_pos)
                skip(parser)

                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
                if parser.buffer[parser.buffer_pos] == '+' || parser.buffer[parser.buffer_pos] == '-' {
                        if parser.buffer[parser.buffer_pos] == '+' {
                                chomping = +1
                        } else {
                                chomping = -1
                        }
                        skip(parser)
                }
        }

        // Eat whitespaces and comments to the end of the line.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        for is_blank(parser.buffer, parser.buffer_pos) {
                skip(parser)
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
        }
        if parser.buffer[parser.buffer_pos] == '#' {
                if !yaml_parser_scan_line_comment(parser, start_mark) {
                        return false
                }
                for !is_breakz(parser.buffer, parser.buffer_pos) {
                        skip(parser)
                        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                return false
                        }
                }
        }

        // Check if we are at the end of the line.
        if !is_breakz(parser.buffer, parser.buffer_pos) {
                yaml_parser_set_scanner_error(parser, "while scanning a block scalar",
                        start_mark, "did not find expected comment or line break")
                return false
        }

        // Eat a line break.
        if is_break(parser.buffer, parser.buffer_pos) {
                if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                        return false
                }
                skip_line(parser)
        }

        end_mark := parser.mark

        // Set the indentation level if it was specified.
        var indent int
        if increment > 0 {
                if parser.indent >= 0 {
                        indent = parser.indent + increment
                } else {
                        indent = increment
                }
        }

        // Scan the leading line breaks and determine the indentation level if needed.
        var s, leading_break, trailing_breaks []byte
        if !yaml_parser_scan_block_scalar_breaks(parser, &indent, &trailing_breaks, start_mark, &end_mark) {
                return false
        }

        // Scan the block scalar content.
        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                return false
        }
        var leading_blank, trailing_blank bool
        for parser.mark.column == indent && !is_z(parser.buffer, parser.buffer_pos) {
                // We are at the beginning of a non-empty line.

                // Is it a trailing whitespace?
                trailing_blank = is_blank(parser.buffer, parser.buffer_pos)

                // Check if we need to fold the leading line break.
                if !literal && !leading_blank && !trailing_blank && len(leading_break) > 0 && leading_break[0] == '\n' {
                        // Do we need to join the lines by space?
                        if len(trailing_breaks) == 0 {
                                s = append(s, ' ')
                        }
                } else {
                        s = append(s, leading_break...)
                }
                leading_break = leading_break[:0]

                // Append the remaining line breaks.
                s = append(s, trailing_breaks...)
                trailing_breaks = trailing_breaks[:0]

                // Is it a leading whitespace?
                leading_blank = is_blank(parser.buffer, parser.buffer_pos)

                // Consume the current line.
                for !is_breakz(parser.buffer, parser.buffer_pos) {
                        s = read(parser, s)
                        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                return false
                        }
                }

                // Consume the line break.
                if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                        return false
                }

                leading_break = read_line(parser, leading_break)

                // Eat the following indentation spaces and line breaks.
                if !yaml_parser_scan_block_scalar_breaks(parser, &indent, &trailing_breaks, start_mark, &end_mark) {
                        return false
                }
        }

        // Chomp the tail.
        if chomping != -1 {
                s = append(s, leading_break...)
        }
        if chomping == 1 {
                s = append(s, trailing_breaks...)
        }

        // Create a token.
        *token = yaml_token_t{
                typ:        yaml_SCALAR_TOKEN,
                start_mark: start_mark,
                end_mark:   end_mark,
                value:      s,
                style:      yaml_LITERAL_SCALAR_STYLE,
        }
        if !literal {
                token.style = yaml_FOLDED_SCALAR_STYLE
        }
        return true
}

// Scan indentation spaces and line breaks for a block scalar.  Determine the
// indentation level if needed.
func yaml_parser_scan_block_scalar_breaks(parser *yaml_parser_t, indent *int, breaks *[]byte, start_mark yaml_mark_t, end_mark *yaml_mark_t) bool {
        *end_mark = parser.mark

        // Eat the indentation spaces and line breaks.
        max_indent := 0
        for {
                // Eat the indentation spaces.
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }
                for (*indent == 0 || parser.mark.column < *indent) && is_space(parser.buffer, parser.buffer_pos) {
                        skip(parser)
                        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                return false
                        }
                }
                if parser.mark.column > max_indent {
                        max_indent = parser.mark.column
                }

                // Check for a tab character messing the indentation.
                if (*indent == 0 || parser.mark.column < *indent) && is_tab(parser.buffer, parser.buffer_pos) {
                        return yaml_parser_set_scanner_error(parser, "while scanning a block scalar",
                                start_mark, "found a tab character where an indentation space is expected")
                }

                // Have we found a non-empty line?
                if !is_break(parser.buffer, parser.buffer_pos) {
                        break
                }

                // Consume the line break.
                if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                        return false
                }
                // [Go] Should really be returning breaks instead.
                *breaks = read_line(parser, *breaks)
                *end_mark = parser.mark
        }

        // Determine the indentation level if needed.
        if *indent == 0 {
                *indent = max_indent
                if *indent < parser.indent+1 {
                        *indent = parser.indent + 1
                }
                if *indent < 1 {
                        *indent = 1
                }
        }
        return true
}

// Scan a quoted scalar.
func yaml_parser_scan_flow_scalar(parser *yaml_parser_t, token *yaml_token_t, single bool) bool {
        // Eat the left quote.
        start_mark := parser.mark
        skip(parser)

        // Consume the content of the quoted scalar.
        var s, leading_break, trailing_breaks, whitespaces []byte
        for {
                // Check that there are no document indicators at the beginning of the line.
                if parser.unread < 4 && !yaml_parser_update_buffer(parser, 4) {
                        return false
                }

                if parser.mark.column == 0 &&
                        ((parser.buffer[parser.buffer_pos+0] == '-' &&
                                parser.buffer[parser.buffer_pos+1] == '-' &&
                                parser.buffer[parser.buffer_pos+2] == '-') ||
                                (parser.buffer[parser.buffer_pos+0] == '.' &&
                                        parser.buffer[parser.buffer_pos+1] == '.' &&
                                        parser.buffer[parser.buffer_pos+2] == '.')) &&
                        is_blankz(parser.buffer, parser.buffer_pos+3) {
                        yaml_parser_set_scanner_error(parser, "while scanning a quoted scalar",
                                start_mark, "found unexpected document indicator")
                        return false
                }

                // Check for EOF.
                if is_z(parser.buffer, parser.buffer_pos) {
                        yaml_parser_set_scanner_error(parser, "while scanning a quoted scalar",
                                start_mark, "found unexpected end of stream")
                        return false
                }

                // Consume non-blank characters.
                leading_blanks := false
                for !is_blankz(parser.buffer, parser.buffer_pos) {
                        if single && parser.buffer[parser.buffer_pos] == '\'' && parser.buffer[parser.buffer_pos+1] == '\'' {
                                // Is is an escaped single quote.
                                s = append(s, '\'')
                                skip(parser)
                                skip(parser)

                        } else if single && parser.buffer[parser.buffer_pos] == '\'' {
                                // It is a right single quote.
                                break
                        } else if !single && parser.buffer[parser.buffer_pos] == '"' {
                                // It is a right double quote.
                                break

                        } else if !single && parser.buffer[parser.buffer_pos] == '\\' && is_break(parser.buffer, parser.buffer_pos+1) {
                                // It is an escaped line break.
                                if parser.unread < 3 && !yaml_parser_update_buffer(parser, 3) {
                                        return false
                                }
                                skip(parser)
                                skip_line(parser)
                                leading_blanks = true
                                break

                        } else if !single && parser.buffer[parser.buffer_pos] == '\\' {
                                // It is an escape sequence.
                                code_length := 0

                                // Check the escape character.
                                switch parser.buffer[parser.buffer_pos+1] {
                                case '0':
                                        s = append(s, 0)
                                case 'a':
                                        s = append(s, '\x07')
                                case 'b':
                                        s = append(s, '\x08')
                                case 't', '\t':
                                        s = append(s, '\x09')
                                case 'n':
                                        s = append(s, '\x0A')
                                case 'v':
                                        s = append(s, '\x0B')
                                case 'f':
                                        s = append(s, '\x0C')
                                case 'r':
                                        s = append(s, '\x0D')
                                case 'e':
                                        s = append(s, '\x1B')
                                case ' ':
                                        s = append(s, '\x20')
                                case '"':
                                        s = append(s, '"')
                                case '\'':
                                        s = append(s, '\'')
                                case '\\':
                                        s = append(s, '\\')
                                case 'N': // NEL (#x85)
                                        s = append(s, '\xC2')
                                        s = append(s, '\x85')
                                case '_': // #xA0
                                        s = append(s, '\xC2')
                                        s = append(s, '\xA0')
                                case 'L': // LS (#x2028)
                                        s = append(s, '\xE2')
                                        s = append(s, '\x80')
                                        s = append(s, '\xA8')
                                case 'P': // PS (#x2029)
                                        s = append(s, '\xE2')
                                        s = append(s, '\x80')
                                        s = append(s, '\xA9')
                                case 'x':
                                        code_length = 2
                                case 'u':
                                        code_length = 4
                                case 'U':
                                        code_length = 8
                                default:
                                        yaml_parser_set_scanner_error(parser, "while parsing a quoted scalar",
                                                start_mark, "found unknown escape character")
                                        return false
                                }

                                skip(parser)
                                skip(parser)

                                // Consume an arbitrary escape code.
                                if code_length > 0 {
                                        var value int

                                        // Scan the character value.
                                        if parser.unread < code_length && !yaml_parser_update_buffer(parser, code_length) {
                                                return false
                                        }
                                        for k := 0; k < code_length; k++ {
                                                if !is_hex(parser.buffer, parser.buffer_pos+k) {
                                                        yaml_parser_set_scanner_error(parser, "while parsing a quoted scalar",
                                                                start_mark, "did not find expected hexdecimal number")
                                                        return false
                                                }
                                                value = (value << 4) + as_hex(parser.buffer, parser.buffer_pos+k)
                                        }

                                        // Check the value and write the character.
                                        if (value >= 0xD800 && value <= 0xDFFF) || value > 0x10FFFF {
                                                yaml_parser_set_scanner_error(parser, "while parsing a quoted scalar",
                                                        start_mark, "found invalid Unicode character escape code")
                                                return false
                                        }
                                        if value <= 0x7F {
                                                s = append(s, byte(value))
                                        } else if value <= 0x7FF {
                                                s = append(s, byte(0xC0+(value>>6)))
                                                s = append(s, byte(0x80+(value&0x3F)))
                                        } else if value <= 0xFFFF {
                                                s = append(s, byte(0xE0+(value>>12)))
                                                s = append(s, byte(0x80+((value>>6)&0x3F)))
                                                s = append(s, byte(0x80+(value&0x3F)))
                                        } else {
                                                s = append(s, byte(0xF0+(value>>18)))
                                                s = append(s, byte(0x80+((value>>12)&0x3F)))
                                                s = append(s, byte(0x80+((value>>6)&0x3F)))
                                                s = append(s, byte(0x80+(value&0x3F)))
                                        }

                                        // Advance the pointer.
                                        for k := 0; k < code_length; k++ {
                                                skip(parser)
                                        }
                                }
                        } else {
                                // It is a non-escaped non-blank character.
                                s = read(parser, s)
                        }
                        if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                                return false
                        }
                }

                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }

                // Check if we are at the end of the scalar.
                if single {
                        if parser.buffer[parser.buffer_pos] == '\'' {
                                break
                        }
                } else {
                        if parser.buffer[parser.buffer_pos] == '"' {
                                break
                        }
                }

                // Consume blank characters.
                for is_blank(parser.buffer, parser.buffer_pos) || is_break(parser.buffer, parser.buffer_pos) {
                        if is_blank(parser.buffer, parser.buffer_pos) {
                                // Consume a space or a tab character.
                                if !leading_blanks {
                                        whitespaces = read(parser, whitespaces)
                                } else {
                                        skip(parser)
                                }
                        } else {
                                if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                                        return false
                                }

                                // Check if it is a first line break.
                                if !leading_blanks {
                                        whitespaces = whitespaces[:0]
                                        leading_break = read_line(parser, leading_break)
                                        leading_blanks = true
                                } else {
                                        trailing_breaks = read_line(parser, trailing_breaks)
                                }
                        }
                        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                return false
                        }
                }

                // Join the whitespaces or fold line breaks.
                if leading_blanks {
                        // Do we need to fold line breaks?
                        if len(leading_break) > 0 && leading_break[0] == '\n' {
                                if len(trailing_breaks) == 0 {
                                        s = append(s, ' ')
                                } else {
                                        s = append(s, trailing_breaks...)
                                }
                        } else {
                                s = append(s, leading_break...)
                                s = append(s, trailing_breaks...)
                        }
                        trailing_breaks = trailing_breaks[:0]
                        leading_break = leading_break[:0]
                } else {
                        s = append(s, whitespaces...)
                        whitespaces = whitespaces[:0]
                }
        }

        // Eat the right quote.
        skip(parser)
        end_mark := parser.mark

        // Create a token.
        *token = yaml_token_t{
                typ:        yaml_SCALAR_TOKEN,
                start_mark: start_mark,
                end_mark:   end_mark,
                value:      s,
                style:      yaml_SINGLE_QUOTED_SCALAR_STYLE,
        }
        if !single {
                token.style = yaml_DOUBLE_QUOTED_SCALAR_STYLE
        }
        return true
}

// Scan a plain scalar.
func yaml_parser_scan_plain_scalar(parser *yaml_parser_t, token *yaml_token_t) bool {

        var s, leading_break, trailing_breaks, whitespaces []byte
        var leading_blanks bool
        var indent = parser.indent + 1

        start_mark := parser.mark
        end_mark := parser.mark

        // Consume the content of the plain scalar.
        for {
                // Check for a document indicator.
                if parser.unread < 4 && !yaml_parser_update_buffer(parser, 4) {
                        return false
                }
                if parser.mark.column == 0 &&
                        ((parser.buffer[parser.buffer_pos+0] == '-' &&
                                parser.buffer[parser.buffer_pos+1] == '-' &&
                                parser.buffer[parser.buffer_pos+2] == '-') ||
                                (parser.buffer[parser.buffer_pos+0] == '.' &&
                                        parser.buffer[parser.buffer_pos+1] == '.' &&
                                        parser.buffer[parser.buffer_pos+2] == '.')) &&
                        is_blankz(parser.buffer, parser.buffer_pos+3) {
                        break
                }

                // Check for a comment.
                if parser.buffer[parser.buffer_pos] == '#' {
                        break
                }

                // Consume non-blank characters.
                for !is_blankz(parser.buffer, parser.buffer_pos) {

                        // Check for indicators that may end a plain scalar.
                        if (parser.buffer[parser.buffer_pos] == ':' && is_blankz(parser.buffer, parser.buffer_pos+1)) ||
                                (parser.flow_level > 0 &&
                                        (parser.buffer[parser.buffer_pos] == ',' ||
                                                parser.buffer[parser.buffer_pos] == '?' || parser.buffer[parser.buffer_pos] == '[' ||
                                                parser.buffer[parser.buffer_pos] == ']' || parser.buffer[parser.buffer_pos] == '{' ||
                                                parser.buffer[parser.buffer_pos] == '}')) {
                                break
                        }

                        // Check if we need to join whitespaces and breaks.
                        if leading_blanks || len(whitespaces) > 0 {
                                if leading_blanks {
                                        // Do we need to fold line breaks?
                                        if leading_break[0] == '\n' {
                                                if len(trailing_breaks) == 0 {
                                                        s = append(s, ' ')
                                                } else {
                                                        s = append(s, trailing_breaks...)
                                                }
                                        } else {
                                                s = append(s, leading_break...)
                                                s = append(s, trailing_breaks...)
                                        }
                                        trailing_breaks = trailing_breaks[:0]
                                        leading_break = leading_break[:0]
                                        leading_blanks = false
                                } else {
                                        s = append(s, whitespaces...)
                                        whitespaces = whitespaces[:0]
                                }
                        }

                        // Copy the character.
                        s = read(parser, s)

                        end_mark = parser.mark
                        if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                                return false
                        }
                }

                // Is it the end?
                if !(is_blank(parser.buffer, parser.buffer_pos) || is_break(parser.buffer, parser.buffer_pos)) {
                        break
                }

                // Consume blank characters.
                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                        return false
                }

                for is_blank(parser.buffer, parser.buffer_pos) || is_break(parser.buffer, parser.buffer_pos) {
                        if is_blank(parser.buffer, parser.buffer_pos) {

                                // Check for tab characters that abuse indentation.
                                if leading_blanks && parser.mark.column < indent && is_tab(parser.buffer, parser.buffer_pos) {
                                        yaml_parser_set_scanner_error(parser, "while scanning a plain scalar",
                                                start_mark, "found a tab character that violates indentation")
                                        return false
                                }

                                // Consume a space or a tab character.
                                if !leading_blanks {
                                        whitespaces = read(parser, whitespaces)
                                } else {
                                        skip(parser)
                                }
                        } else {
                                if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                                        return false
                                }

                                // Check if it is a first line break.
                                if !leading_blanks {
                                        whitespaces = whitespaces[:0]
                                        leading_break = read_line(parser, leading_break)
                                        leading_blanks = true
                                } else {
                                        trailing_breaks = read_line(parser, trailing_breaks)
                                }
                        }
                        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                return false
                        }
                }

                // Check indentation level.
                if parser.flow_level == 0 && parser.mark.column < indent {
                        break
                }
        }

        // Create a token.
        *token = yaml_token_t{
                typ:        yaml_SCALAR_TOKEN,
                start_mark: start_mark,
                end_mark:   end_mark,
                value:      s,
                style:      yaml_PLAIN_SCALAR_STYLE,
        }

        // Note that we change the 'simple_key_allowed' flag.
        if leading_blanks {
                parser.simple_key_allowed = true
        }
        return true
}

func yaml_parser_scan_line_comment(parser *yaml_parser_t, token_mark yaml_mark_t) bool {
        if parser.newlines > 0 {
                return true
        }

        var start_mark yaml_mark_t
        var text []byte

        for peek := 0; peek < 512; peek++ {
                if parser.unread < peek+1 && !yaml_parser_update_buffer(parser, peek+1) {
                        break
                }
                if is_blank(parser.buffer, parser.buffer_pos+peek) {
                        continue
                }
                if parser.buffer[parser.buffer_pos+peek] == '#' {
                        seen := parser.mark.index+peek
                        for {
                                if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                        return false
                                }
                                if is_breakz(parser.buffer, parser.buffer_pos) {
                                        if parser.mark.index >= seen {
                                                break
                                        }
                                        if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                                                return false
                                        }
                                        skip_line(parser)
                                } else if parser.mark.index >= seen {
                                        if len(text) == 0 {
                                                start_mark = parser.mark
                                        }
                                        text = read(parser, text)
                                } else {
                                        skip(parser)
                                }
                        }
                }
                break
        }
        if len(text) > 0 {
                parser.comments = append(parser.comments, yaml_comment_t{
                        token_mark: token_mark,
                        start_mark: start_mark,
                        line: text,
                })
        }
        return true
}

func yaml_parser_scan_comments(parser *yaml_parser_t, scan_mark yaml_mark_t) bool {
        token := parser.tokens[len(parser.tokens)-1]

        if token.typ == yaml_FLOW_ENTRY_TOKEN && len(parser.tokens) > 1 {
                token = parser.tokens[len(parser.tokens)-2]
        }

        var token_mark = token.start_mark
        var start_mark yaml_mark_t
        var next_indent = parser.indent
        if next_indent < 0 {
                next_indent = 0
        }

        var recent_empty = false
        var first_empty = parser.newlines <= 1

        var line = parser.mark.line
        var column = parser.mark.column

        var text []byte

        // The foot line is the place where a comment must start to
        // still be considered as a foot of the prior content.
        // If there's some content in the currently parsed line, then
        // the foot is the line below it.
        var foot_line = -1
        if scan_mark.line > 0 {
                foot_line = parser.mark.line-parser.newlines+1
                if parser.newlines == 0 && parser.mark.column > 1 {
                        foot_line++
                }
        }

        var peek = 0
        for ; peek < 512; peek++ {
                if parser.unread < peek+1 && !yaml_parser_update_buffer(parser, peek+1) {
                        break
                }
                column++
                if is_blank(parser.buffer, parser.buffer_pos+peek) {
                        continue
                }
                c := parser.buffer[parser.buffer_pos+peek]
                var close_flow = parser.flow_level > 0 && (c == ']' || c == '}')
                if close_flow || is_breakz(parser.buffer, parser.buffer_pos+peek) {
                        // Got line break or terminator.
                        if close_flow || !recent_empty {
                                if close_flow || first_empty && (start_mark.line == foot_line && token.typ != yaml_VALUE_TOKEN || start_mark.column-1 < next_indent) {
                                        // This is the first empty line and there were no empty lines before,
                                        // so this initial part of the comment is a foot of the prior token
                                        // instead of being a head for the following one. Split it up.
                                        // Alternatively, this might also be the last comment inside a flow
                                        // scope, so it must be a footer.
                                        if len(text) > 0 {
                                                if start_mark.column-1 < next_indent {
                                                        // If dedented it's unrelated to the prior token.
                                                        token_mark = start_mark
                                                }
                                                parser.comments = append(parser.comments, yaml_comment_t{
                                                        scan_mark:  scan_mark,
                                                        token_mark: token_mark,
                                                        start_mark: start_mark,
                                                        end_mark:   yaml_mark_t{parser.mark.index + peek, line, column},
                                                        foot:       text,
                                                })
                                                scan_mark = yaml_mark_t{parser.mark.index + peek, line, column}
                                                token_mark = scan_mark
                                                text = nil
                                        }
                                } else {
                                        if len(text) > 0 && parser.buffer[parser.buffer_pos+peek] != 0 {
                                                text = append(text, '\n')
                                        }
                                }
                        }
                        if !is_break(parser.buffer, parser.buffer_pos+peek) {
                                break
                        }
                        first_empty = false
                        recent_empty = true
                        column = 0
                        line++
                        continue
                }

                if len(text) > 0 && (close_flow || column-1 < next_indent && column != start_mark.column) {
                        // The comment at the different indentation is a foot of the
                        // preceding data rather than a head of the upcoming one.
                        parser.comments = append(parser.comments, yaml_comment_t{
                                scan_mark:  scan_mark,
                                token_mark: token_mark,
                                start_mark: start_mark,
                                end_mark:   yaml_mark_t{parser.mark.index + peek, line, column},
                                foot:       text,
                        })
                        scan_mark = yaml_mark_t{parser.mark.index + peek, line, column}
                        token_mark = scan_mark
                        text = nil
                }

                if parser.buffer[parser.buffer_pos+peek] != '#' {
                        break
                }

                if len(text) == 0 {
                        start_mark = yaml_mark_t{parser.mark.index + peek, line, column}
                } else {
                        text = append(text, '\n')
                }

                recent_empty = false

                // Consume until after the consumed comment line.
                seen := parser.mark.index+peek
                for {
                        if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
                                return false
                        }
                        if is_breakz(parser.buffer, parser.buffer_pos) {
                                if parser.mark.index >= seen {
                                        break
                                }
                                if parser.unread < 2 && !yaml_parser_update_buffer(parser, 2) {
                                        return false
                                }
                                skip_line(parser)
                        } else if parser.mark.index >= seen {
                                text = read(parser, text)
                        } else {
                                skip(parser)
                        }
                }

                peek = 0
                column = 0
                line = parser.mark.line
                next_indent = parser.indent
                if next_indent < 0 {
                        next_indent = 0
                }
        }

        if len(text) > 0 {
                parser.comments = append(parser.comments, yaml_comment_t{
                        scan_mark:  scan_mark,
                        token_mark: start_mark,
                        start_mark: start_mark,
                        end_mark:   yaml_mark_t{parser.mark.index + peek - 1, line, column},
                        head:       text,
                })
        }
        return true
}
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