Class: Psych::Parser

Inherits:

Object

• Object
• Psych::Parser

Defined in:

lib/psych/parser.rb,
psych_parser.c

Overview

YAML event parser class. This class parses a YAML document and calls events on the handler that is passed to the constructor. The events can be used for things such as constructing a YAML AST or deserializing YAML documents. It can even be fed back to Psych::Emitter to emit the same document that was parsed.

See Psych::Handler for documentation on the events that Psych::Parser emits.

Here is an example that prints out ever scalar found in a YAML document:

# Handler for detecting scalar values
class ScalarHandler < Psych::Handler
  def scalar value, anchor, tag, plain, quoted, style
    puts value
  end
end

parser = Psych::Parser.new(ScalarHandler.new)
parser.parse(yaml_document)

Here is an example that feeds the parser back in to Psych::Emitter. The YAML document is read from STDIN and written back out to STDERR:

parser = Psych::Parser.new(Psych::Emitter.new($stderr))
parser.parse($stdin)

Psych uses Psych::Parser in combination with Psych::TreeBuilder to construct an AST of the parsed YAML document.

Defined Under Namespace

Classes: Mark

Constant Summary

ANY =

Let the parser choose the encoding

Any encoding

UTF8 =

UTF-8 Encoding

INT2NUM(YAML_UTF8_ENCODING)

UTF16LE =

UTF-16-LE Encoding with BOM

INT2NUM(YAML_UTF16LE_ENCODING)

UTF16BE =

UTF-16-BE Encoding with BOM

INT2NUM(YAML_UTF16BE_ENCODING)

Instance Attribute Summary

• #external_encoding ⇒ Object writeonly

  Set the encoding for this parser to encoding.

• #handler ⇒ Object

  The handler on which events will be called.

Instance Method Summary

• #initialize(handler = Handler.new) ⇒ Parser constructor

  Creates a new Psych::Parser instance with handler.

• #mark ⇒ Object

  Returns a Psych::Parser::Mark object that contains line, column, and index information.

• #parse(yaml) ⇒ Object

  Parse the YAML document contained in yaml.

Constructor Details

#initialize(handler = Handler.new) ⇒ Parser

Creates a new Psych::Parser instance with handler. YAML events will be called on handler. See Psych::Parser for more details.

# File 'lib/psych/parser.rb', line 47

def initialize handler = Handler.new
  @handler = handler
  @external_encoding = ANY
end

Instance Attribute Details

#external_encoding=(value) ⇒ Object (writeonly)

Set the encoding for this parser to encoding

# File 'lib/psych/parser.rb', line 41

def external_encoding=(value)
  @external_encoding = value
end

#handler ⇒ Object

The handler on which events will be called

# File 'lib/psych/parser.rb', line 38

def handler
  @handler
end

Instance Method Details

#mark ⇒ Object

Returns a Psych::Parser::Mark object that contains line, column, and index information.

# File 'psych_parser.c', line 522

static VALUE mark(VALUE self)
{
    VALUE mark_klass;
    VALUE args[3];
    yaml_parser_t * parser;

    TypedData_Get_Struct(self, yaml_parser_t, &psych_parser_type, parser);
    mark_klass = rb_const_get_at(cPsychParser, rb_intern("Mark"));
    args[0] = SIZET2NUM(parser->mark.index);
    args[1] = SIZET2NUM(parser->mark.line);
    args[2] = SIZET2NUM(parser->mark.column);

    return rb_class_new_instance(3, args, mark_klass);
}

#parse(yaml) ⇒ Object

Parse the YAML document contained in yaml. Events will be called on the handler set on the parser instance.

See Psych::Parser and Psych::Parser#handler

# File 'psych_parser.c', line 253

static VALUE parse(int argc, VALUE *argv, VALUE self)
{
    VALUE yaml, path;
    yaml_parser_t * parser;
    yaml_event_t event;
    int done = 0;
    int state = 0;
    int parser_encoding = YAML_ANY_ENCODING;
    int encoding = rb_utf8_encindex();
    rb_encoding * internal_enc = rb_default_internal_encoding();
    VALUE handler = rb_iv_get(self, "@handler");

    if (rb_scan_args(argc, argv, "11", &yaml, &path) == 1) {
	if(rb_respond_to(yaml, id_path))
	    path = rb_funcall(yaml, id_path, 0);
	else
	    path = rb_str_new2("<unknown>");
    }

    TypedData_Get_Struct(self, yaml_parser_t, &psych_parser_type, parser);

    yaml_parser_delete(parser);
    yaml_parser_initialize(parser);

    if (rb_respond_to(yaml, id_read)) {
	yaml = transcode_io(yaml, &parser_encoding);
	yaml_parser_set_encoding(parser, parser_encoding);
	yaml_parser_set_input(parser, io_reader, (void *)yaml);
    } else {
	StringValue(yaml);
	yaml = transcode_string(yaml, &parser_encoding);
	yaml_parser_set_encoding(parser, parser_encoding);
	yaml_parser_set_input_string(
		parser,
		(const unsigned char *)RSTRING_PTR(yaml),
		(size_t)RSTRING_LEN(yaml)
		);
    }

    while(!done) {
	VALUE event_args[5];
	VALUE start_line, start_column, end_line, end_column;

	if(!yaml_parser_parse(parser, &event)) {
	    VALUE exception;

	    exception = make_exception(parser, path);
	    yaml_parser_delete(parser);
	    yaml_parser_initialize(parser);

	    rb_exc_raise(exception);
	}

	start_line = SIZET2NUM(event.start_mark.line);
	start_column = SIZET2NUM(event.start_mark.column);
	end_line = SIZET2NUM(event.end_mark.line);
	end_column = SIZET2NUM(event.end_mark.column);

	event_args[0] = handler;
	event_args[1] = start_line;
	event_args[2] = start_column;
	event_args[3] = end_line;
	event_args[4] = end_column;
	rb_protect(protected_event_location, (VALUE)event_args, &state);

	switch(event.type) {
	    case YAML_STREAM_START_EVENT:
	      {
		  VALUE args[2];

		  args[0] = handler;
		  args[1] = INT2NUM(event.data.stream_start.encoding);
		  rb_protect(protected_start_stream, (VALUE)args, &state);
	      }
	      break;
	  case YAML_DOCUMENT_START_EVENT:
	    {
		VALUE args[4];
		/* Get a list of tag directives (if any) */
		VALUE tag_directives = rb_ary_new();
		/* Grab the document version */
		VALUE version = event.data.document_start.version_directive ?
		    rb_ary_new3(
			(long)2,
			INT2NUM(event.data.document_start.version_directive->major),
			INT2NUM(event.data.document_start.version_directive->minor)
			) : rb_ary_new();

		if(event.data.document_start.tag_directives.start) {
		    yaml_tag_directive_t *start =
			event.data.document_start.tag_directives.start;
		    yaml_tag_directive_t *end =
			event.data.document_start.tag_directives.end;
		    for(; start != end; start++) {
			VALUE handle = Qnil;
			VALUE prefix = Qnil;
			if(start->handle) {
			    handle = rb_str_new2((const char *)start->handle);
			    PSYCH_TRANSCODE(handle, encoding, internal_enc);
			}

			if(start->prefix) {
			    prefix = rb_str_new2((const char *)start->prefix);
			    PSYCH_TRANSCODE(prefix, encoding, internal_enc);
			}

			rb_ary_push(tag_directives, rb_ary_new3((long)2, handle, prefix));
		    }
		}
		args[0] = handler;
		args[1] = version;
		args[2] = tag_directives;
		args[3] = event.data.document_start.implicit == 1 ? Qtrue : Qfalse;
		rb_protect(protected_start_document, (VALUE)args, &state);
	    }
	    break;
	  case YAML_DOCUMENT_END_EVENT:
	    {
		VALUE args[2];

		args[0] = handler;
		args[1] = event.data.document_end.implicit == 1 ? Qtrue : Qfalse;
		rb_protect(protected_end_document, (VALUE)args, &state);
	    }
	    break;
	  case YAML_ALIAS_EVENT:
	    {
		VALUE args[2];
		VALUE alias = Qnil;
		if(event.data.alias.anchor) {
		    alias = rb_str_new2((const char *)event.data.alias.anchor);
		    PSYCH_TRANSCODE(alias, encoding, internal_enc);
		}

		args[0] = handler;
		args[1] = alias;
		rb_protect(protected_alias, (VALUE)args, &state);
	    }
	    break;
	  case YAML_SCALAR_EVENT:
	    {
		VALUE args[7];
		VALUE anchor = Qnil;
		VALUE tag = Qnil;
		VALUE plain_implicit, quoted_implicit, style;
		VALUE val = rb_str_new(
		    (const char *)event.data.scalar.value,
		    (long)event.data.scalar.length
		    );

		PSYCH_TRANSCODE(val, encoding, internal_enc);

		if(event.data.scalar.anchor) {
		    anchor = rb_str_new2((const char *)event.data.scalar.anchor);
		    PSYCH_TRANSCODE(anchor, encoding, internal_enc);
		}

		if(event.data.scalar.tag) {
		    tag = rb_str_new2((const char *)event.data.scalar.tag);
		    PSYCH_TRANSCODE(tag, encoding, internal_enc);
		}

		plain_implicit =
		    event.data.scalar.plain_implicit == 0 ? Qfalse : Qtrue;

		quoted_implicit =
		    event.data.scalar.quoted_implicit == 0 ? Qfalse : Qtrue;

		style = INT2NUM(event.data.scalar.style);

		args[0] = handler;
		args[1] = val;
		args[2] = anchor;
		args[3] = tag;
		args[4] = plain_implicit;
		args[5] = quoted_implicit;
		args[6] = style;
		rb_protect(protected_scalar, (VALUE)args, &state);
	    }
	    break;
	  case YAML_SEQUENCE_START_EVENT:
	    {
		VALUE args[5];
		VALUE anchor = Qnil;
		VALUE tag = Qnil;
		VALUE implicit, style;
		if(event.data.sequence_start.anchor) {
		    anchor = rb_str_new2((const char *)event.data.sequence_start.anchor);
		    PSYCH_TRANSCODE(anchor, encoding, internal_enc);
		}

		tag = Qnil;
		if(event.data.sequence_start.tag) {
		    tag = rb_str_new2((const char *)event.data.sequence_start.tag);
		    PSYCH_TRANSCODE(tag, encoding, internal_enc);
		}

		implicit =
		    event.data.sequence_start.implicit == 0 ? Qfalse : Qtrue;

		style = INT2NUM(event.data.sequence_start.style);

		args[0] = handler;
		args[1] = anchor;
		args[2] = tag;
		args[3] = implicit;
		args[4] = style;

		rb_protect(protected_start_sequence, (VALUE)args, &state);
	    }
	    break;
	  case YAML_SEQUENCE_END_EVENT:
	    rb_protect(protected_end_sequence, handler, &state);
	    break;
	  case YAML_MAPPING_START_EVENT:
	    {
		VALUE args[5];
		VALUE anchor = Qnil;
		VALUE tag = Qnil;
		VALUE implicit, style;
		if(event.data.mapping_start.anchor) {
		    anchor = rb_str_new2((const char *)event.data.mapping_start.anchor);
		    PSYCH_TRANSCODE(anchor, encoding, internal_enc);
		}

		if(event.data.mapping_start.tag) {
		    tag = rb_str_new2((const char *)event.data.mapping_start.tag);
		    PSYCH_TRANSCODE(tag, encoding, internal_enc);
		}

		implicit =
		    event.data.mapping_start.implicit == 0 ? Qfalse : Qtrue;

		style = INT2NUM(event.data.mapping_start.style);

		args[0] = handler;
		args[1] = anchor;
		args[2] = tag;
		args[3] = implicit;
		args[4] = style;

		rb_protect(protected_start_mapping, (VALUE)args, &state);
	    }
	    break;
	  case YAML_MAPPING_END_EVENT:
	    rb_protect(protected_end_mapping, handler, &state);
	    break;
	  case YAML_NO_EVENT:
	    rb_protect(protected_empty, handler, &state);
	    break;
	  case YAML_STREAM_END_EVENT:
	    rb_protect(protected_end_stream, handler, &state);
	    done = 1;
	    break;
	}
	yaml_event_delete(&event);
	if (state) rb_jump_tag(state);
    }

    return self;
}