Module: Psych

Defined in:
lib/psych.rb,
lib/psych/set.rb,
lib/psych/omap.rb,
lib/psych/nodes.rb,
lib/psych/coder.rb,
lib/psych/stream.rb,
lib/psych/parser.rb,
lib/psych/handler.rb,
lib/psych/exception.rb,
lib/psych/streaming.rb,
lib/psych/nodes/node.rb,
lib/psych/deprecated.rb,
lib/psych/nodes/alias.rb,
lib/psych/json/stream.rb,
lib/psych/nodes/scalar.rb,
lib/psych/class_loader.rb,
lib/psych/syntax_error.rb,
lib/psych/nodes/stream.rb,
lib/psych/tree_builder.rb,
lib/psych/nodes/mapping.rb,
lib/psych/scalar_scanner.rb,
lib/psych/nodes/document.rb,
lib/psych/nodes/sequence.rb,
lib/psych/json/ruby_events.rb,
lib/psych/json/yaml_events.rb,
lib/psych/visitors/emitter.rb,
lib/psych/visitors/to_ruby.rb,
lib/psych/visitors/visitor.rb,
lib/psych/json/tree_builder.rb,
lib/psych/handlers/recorder.rb,
lib/psych/visitors/json_tree.rb,
lib/psych/visitors/yaml_tree.rb,
lib/psych/visitors/depth_first.rb,
lib/psych/handlers/document_stream.rb,
psych.c,
psych_parser.c,
psych_emitter.c,
psych_to_ruby.c,
psych_yaml_tree.c

Overview

Overview

Psych is a YAML parser and emitter. Psych leverages libyaml [Home page: pyyaml.org/wiki/LibYAML] or [Git repo: github.com/zerotao/libyaml] for its YAML parsing and emitting capabilities. In addition to wrapping libyaml, Psych also knows how to serialize and de-serialize most Ruby objects to and from the YAML format.

I NEED TO PARSE OR EMIT YAML RIGHT NOW!

# Parse some YAML
Psych.load("--- foo") # => "foo"

# Emit some YAML
Psych.dump("foo")     # => "--- foo\n...\n"
{ :a => 'b'}.to_yaml  # => "---\n:a: b\n"

Got more time on your hands? Keep on reading!

YAML Parsing

Psych provides a range of interfaces for parsing a YAML document ranging from low level to high level, depending on your parsing needs. At the lowest level, is an event based parser. Mid level is access to the raw YAML AST, and at the highest level is the ability to unmarshal YAML to Ruby objects.

YAML Emitting

Psych provides a range of interfaces ranging from low to high level for producing YAML documents. Very similar to the YAML parsing interfaces, Psych provides at the lowest level, an event based system, mid-level is building a YAML AST, and the highest level is converting a Ruby object straight to a YAML document.

High-level API

Parsing

The high level YAML parser provided by Psych simply takes YAML as input and returns a Ruby data structure. For information on using the high level parser see Psych.load

Reading from a string

Psych.load("--- a")             # => 'a'
Psych.load("---\n - a\n - b")   # => ['a', 'b']

Reading from a file

Psych.load_file("database.yml")

Exception handling

begin
  # The second argument chnages only the exception contents
  Psych.parse("--- `", "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

Emitting

The high level emitter has the easiest interface. Psych simply takes a Ruby data structure and converts it to a YAML document. See Psych.dump for more information on dumping a Ruby data structure.

Writing to a string

# Dump an array, get back a YAML string
Psych.dump(['a', 'b'])  # => "---\n- a\n- b\n"

# Dump an array to an IO object
Psych.dump(['a', 'b'], StringIO.new)  # => #<StringIO:0x000001009d0890>

# Dump an array with indentation set
Psych.dump(['a', ['b']], :indentation => 3) # => "---\n- a\n-  - b\n"

# Dump an array to an IO with indentation set
Psych.dump(['a', ['b']], StringIO.new, :indentation => 3)

Writing to a file

Currently there is no direct API for dumping Ruby structure to file:

File.open('database.yml', 'w') do |file|
  file.write(Psych.dump(['a', 'b']))
end

Mid-level API

Parsing

Psych provides access to an AST produced from parsing a YAML document. This tree is built using the Psych::Parser and Psych::TreeBuilder. The AST can be examined and manipulated freely. Please see Psych::parse_stream, Psych::Nodes, and Psych::Nodes::Node for more information on dealing with YAML syntax trees.

Reading from a string

# Returns Psych::Nodes::Stream
Psych.parse_stream("---\n - a\n - b")

# Returns Psych::Nodes::Document
Psych.parse("---\n - a\n - b")

Reading from a file

# Returns Psych::Nodes::Stream
Psych.parse_stream(File.read('database.yml'))

# Returns Psych::Nodes::Document
Psych.parse_file('database.yml')

Exception handling

begin
  # The second argument chnages only the exception contents
  Psych.parse("--- `", "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

Emitting

At the mid level is building an AST. This AST is exactly the same as the AST used when parsing a YAML document. Users can build an AST by hand and the AST knows how to emit itself as a YAML document. See Psych::Nodes, Psych::Nodes::Node, and Psych::TreeBuilder for more information on building a YAML AST.

Writing to a string

# We need Psych::Nodes::Stream (not Psych::Nodes::Document)
stream = Psych.parse_stream("---\n - a\n - b")

stream.to_yaml # => "---\n- a\n- b\n"

Writing to a file

# We need Psych::Nodes::Stream (not Psych::Nodes::Document)
stream = Psych.parse_stream(File.read('database.yml'))

File.open('database.yml', 'w') do |file|
  file.write(stream.to_yaml)
end

Low-level API

Parsing

The lowest level parser should be used when the YAML input is already known, and the developer does not want to pay the price of building an AST or automatic detection and conversion to Ruby objects. See Psych::Parser for more information on using the event based parser.

Reading to Psych::Nodes::Stream structure

parser = Psych::Parser.new(TreeBuilder.new) # => #<Psych::Parser>
parser = Psych.parser                       # it's an alias for the above

parser.parse("---\n - a\n - b")             # => #<Psych::Parser>
parser.handler                              # => #<Psych::TreeBuilder>
parser.handler.root                         # => #<Psych::Nodes::Stream>

Receiving an events stream

parser = Psych::Parser.new(Psych::Handlers::Recorder.new)

parser.parse("---\n - a\n - b")
parser.events # => [list of [event, args] lists]
              # event is one of: Psych::Handler::EVENTS
              # args are the arguments passed to the event

Emitting

The lowest level emitter is an event based system. Events are sent to a Psych::Emitter object. That object knows how to convert the events to a YAML document. This interface should be used when document format is known in advance or speed is a concern. See Psych::Emitter for more information.

Writing to a Ruby structure

Psych.parser.parse("--- a")       # => #<Psych::Parser>

parser.handler.first              # => #<Psych::Nodes::Stream>
parser.handler.first.to_ruby      # => ["a"]

parser.handler.root.first         # => #<Psych::Nodes::Document>
parser.handler.root.first.to_ruby # => "a"

# You can instantiate an Emitter manually
Psych::Visitors::ToRuby.new.accept(parser.handler.root.first)
# => "a"

Defined Under Namespace

Modules: DeprecatedMethods, Handlers, JSON, Nodes, Streaming, Visitors Classes: BadAlias, ClassLoader, Coder, DisallowedClass, Emitter, Exception, Handler, Omap, Parser, ScalarScanner, Set, Stream, SyntaxError, TreeBuilder

Constant Summary collapse

VERSION =

The version is Psych you're using

'2.0.2'
LIBYAML_VERSION =

The version of libyaml Psych is using

Psych.libyaml_version.join '.'
DEPRECATED =

:nodoc:

__FILE__

Class Attribute Summary collapse

Class Method Summary collapse

Class Attribute Details

.domain_typesObject

Returns the value of attribute domain_types



494
495
496
# File 'lib/psych.rb', line 494

def domain_types
  @domain_types
end

.dump_tagsObject

Returns the value of attribute dump_tags



493
494
495
# File 'lib/psych.rb', line 493

def dump_tags
  @dump_tags
end

.load_tagsObject

Returns the value of attribute load_tags



492
493
494
# File 'lib/psych.rb', line 492

def load_tags
  @load_tags
end

Class Method Details

.add_builtin_type(type_tag, &block) ⇒ Object



474
475
476
477
478
# File 'lib/psych.rb', line 474

def self.add_builtin_type type_tag, &block
  domain = 'yaml.org,2002'
  key = ['tag', domain, type_tag].join ':'
  @domain_types[key] = [key, block]
end

.add_domain_type(domain, type_tag, &block) ⇒ Object



468
469
470
471
472
# File 'lib/psych.rb', line 468

def self.add_domain_type domain, type_tag, &block
  key = ['tag', domain, type_tag].join ':'
  @domain_types[key] = [key, block]
  @domain_types["tag:#{type_tag}"] = [key, block]
end

.add_private_type(type_tag, &block) ⇒ Object



49
50
51
52
53
54
# File 'lib/psych/deprecated.rb', line 49

def self.add_private_type type_tag, &block
  warn "#{caller[0]}: add_private_type is deprecated, use add_domain_type" if $VERBOSE
  domain = 'x-private'
  key = [domain, type_tag].join ':'
  @domain_types[key] = [key, block]
end

.add_ruby_type(type_tag, &block) ⇒ Object



42
43
44
45
46
47
# File 'lib/psych/deprecated.rb', line 42

def self.add_ruby_type type_tag, &block
  warn "#{caller[0]}: add_ruby_type is deprecated, use add_domain_type" if $VERBOSE
  domain = 'ruby.yaml.org,2002'
  key = ['tag', domain, type_tag].join ':'
  @domain_types[key] = [key, block]
end

.add_tag(tag, klass) ⇒ Object



486
487
488
489
# File 'lib/psych.rb', line 486

def self.add_tag tag, klass
  @load_tags[tag] = klass.name
  @dump_tags[klass] = tag
end

.detect_implicit(thing) ⇒ Object



34
35
36
37
38
39
40
# File 'lib/psych/deprecated.rb', line 34

def self.detect_implicit thing
  warn "#{caller[0]}: detect_implicit is deprecated" if $VERBOSE
  return '' unless String === thing
  return 'null' if '' == thing
  ss = ScalarScanner.new(ClassLoader.new)
  ss.tokenize(thing).class.name.downcase
end

.dump(o, io = nil, options = {}) ⇒ Object

call-seq:

Psych.dump(o)               -> string of yaml
Psych.dump(o, options)      -> string of yaml
Psych.dump(o, io)           -> io object passed in
Psych.dump(o, io, options)  -> io object passed in

Dump Ruby object o to a YAML string. Optional options may be passed in to control the output format. If an IO object is passed in, the YAML will be dumped to that IO object.

Example:

# Dump an array, get back a YAML string
Psych.dump(['a', 'b'])  # => "---\n- a\n- b\n"

# Dump an array to an IO object
Psych.dump(['a', 'b'], StringIO.new)  # => #<StringIO:0x000001009d0890>

# Dump an array with indentation set
Psych.dump(['a', ['b']], :indentation => 3) # => "---\n- a\n-  - b\n"

# Dump an array to an IO with indentation set
Psych.dump(['a', ['b']], StringIO.new, :indentation => 3)


401
402
403
404
405
406
407
408
409
410
# File 'lib/psych.rb', line 401

def self.dump o, io = nil, options = {}
  if Hash === io
    options = io
    io      = nil
  end

  visitor = Psych::Visitors::YAMLTree.create options
  visitor << o
  visitor.tree.yaml io, options
end

.dump_stream(*objects) ⇒ Object

Dump a list of objects as separate documents to a document stream.

Example:

Psych.dump_stream("foo\n  ", {}) # => "--- ! \"foo\\n  \"\n--- {}\n"


418
419
420
421
422
423
424
# File 'lib/psych.rb', line 418

def self.dump_stream *objects
  visitor = Psych::Visitors::YAMLTree.create({})
  objects.each do |o|
    visitor << o
  end
  visitor.tree.yaml
end

.libyaml_versionObject

Returns the version of libyaml being used



7
8
9
10
11
12
13
14
15
16
17
18
19
# File 'psych.c', line 7

static VALUE libyaml_version(VALUE module)
{
    int major, minor, patch;
    VALUE list[3];

    yaml_get_version(&major, &minor, &patch);

    list[0] = INT2NUM((long)major);
    list[1] = INT2NUM((long)minor);
    list[2] = INT2NUM((long)patch);

    return rb_ary_new4((long)3, list);
}

.load(yaml, filename = nil) ⇒ Object

Load yaml in to a Ruby data structure. If multiple documents are provided, the object contained in the first document will be returned. filename will be used in the exception message if any exception is raised while parsing.

Raises a Psych::SyntaxError when a YAML syntax error is detected.

Example:

Psych.load("--- a")             # => 'a'
Psych.load("---\n - a\n - b")   # => ['a', 'b']

begin
  Psych.load("--- `", "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end


243
244
245
246
# File 'lib/psych.rb', line 243

def self.load yaml, filename = nil
  result = parse(yaml, filename)
  result ? result.to_ruby : result
end

.load_documents(yaml, &block) ⇒ Object

This method is deprecated, use Psych.load_stream instead.



25
26
27
28
29
30
31
32
# File 'lib/psych/deprecated.rb', line 25

def self.load_documents yaml, &block
  if $VERBOSE
    warn "#{caller[0]}: load_documents is deprecated, use load_stream"
  end
  list = load_stream yaml
  return list unless block_given?
  list.each(&block)
end

.load_file(filename) ⇒ Object

Load the document contained in filename. Returns the yaml contained in filename as a Ruby object



462
463
464
# File 'lib/psych.rb', line 462

def self.load_file filename
  File.open(filename, 'r:bom|utf-8') { |f| self.load f, filename }
end

.load_stream(yaml, filename = nil) ⇒ Object

Load multiple documents given in yaml. Returns the parsed documents as a list. If a block is given, each document will be converted to Ruby and passed to the block during parsing

Example:

Psych.load_stream("--- foo\n...\n--- bar\n...") # => ['foo', 'bar']

list = []
Psych.load_stream("--- foo\n...\n--- bar\n...") do |ruby|
  list << ruby
end
list # => ['foo', 'bar']


449
450
451
452
453
454
455
456
457
# File 'lib/psych.rb', line 449

def self.load_stream yaml, filename = nil
  if block_given?
    parse_stream(yaml, filename) do |node|
      yield node.to_ruby
    end
  else
    parse_stream(yaml, filename).children.map { |child| child.to_ruby }
  end
end

.object_maker(klass, hash) ⇒ Object



72
73
74
75
76
77
# File 'lib/psych/deprecated.rb', line 72

def self.object_maker klass, hash
  warn "#{caller[0]}: object_maker is deprecated" if $VERBOSE
  klass.allocate.tap do |obj|
    hash.each { |k,v| obj.instance_variable_set(:"@#{k}", v) }
  end
end

.parse(yaml, filename = nil) ⇒ Object

Parse a YAML string in yaml. Returns the Psych::Nodes::Document. filename is used in the exception message if a Psych::SyntaxError is raised.

Raises a Psych::SyntaxError when a YAML syntax error is detected.

Example:

Psych.parse("---\n - a\n - b") # => #<Psych::Nodes::Document:0x00>

begin
  Psych.parse("--- `", "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

See Psych::Nodes for more information about YAML AST.



316
317
318
319
320
321
# File 'lib/psych.rb', line 316

def self.parse yaml, filename = nil
  parse_stream(yaml, filename) do |node|
    return node
  end
  false
end

.parse_file(filename) ⇒ Object

Parse a file at filename. Returns the Psych::Nodes::Document.

Raises a Psych::SyntaxError when a YAML syntax error is detected.



327
328
329
330
331
# File 'lib/psych.rb', line 327

def self.parse_file filename
  File.open filename, 'r:bom|utf-8' do |f|
    parse f, filename
  end
end

.parse_stream(yaml, filename = nil, &block) ⇒ Object

Parse a YAML string in yaml. Returns the Psych::Nodes::Stream. This method can handle multiple YAML documents contained in yaml. filename is used in the exception message if a Psych::SyntaxError is raised.

If a block is given, a Psych::Nodes::Document node will be yielded to the block as it's being parsed.

Raises a Psych::SyntaxError when a YAML syntax error is detected.

Example:

Psych.parse_stream("---\n - a\n - b") # => #<Psych::Nodes::Stream:0x00>

Psych.parse_stream("--- a\n--- b") do |node|
  node # => #<Psych::Nodes::Document:0x00>
end

begin
  Psych.parse_stream("--- `", "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

See Psych::Nodes for more information about YAML AST.



366
367
368
369
370
371
372
373
374
375
# File 'lib/psych.rb', line 366

def self.parse_stream yaml, filename = nil, &block
  if block_given?
    parser = Psych::Parser.new(Handlers::DocumentStream.new(&block))
    parser.parse yaml, filename
  else
    parser = self.parser
    parser.parse yaml, filename
    parser.handler.root
  end
end

.parserObject

Returns a default parser



335
336
337
# File 'lib/psych.rb', line 335

def self.parser
  Psych::Parser.new(TreeBuilder.new)
end

.quick_emit(thing, opts = {}, &block) ⇒ Object

:nodoc:



11
12
13
14
15
16
17
18
19
20
21
22
# File 'lib/psych/deprecated.rb', line 11

def self.quick_emit thing, opts = {}, &block # :nodoc:
  warn "#{caller[0]}: YAML.quick_emit is deprecated" if $VERBOSE && !caller[0].start_with?(File.dirname(__FILE__))
  target = eval 'self', block.binding
  target.extend DeprecatedMethods
  metaclass = class << target; self; end
  metaclass.send(:define_method, :encode_with) do |coder|
    target.taguri        = coder.tag
    target.to_yaml_style = coder.style
    block.call coder
  end
  target.psych_to_yaml unless opts[:nodump]
end

.read_type_class(type, reference) ⇒ Object



62
63
64
65
66
67
68
69
70
# File 'lib/psych/deprecated.rb', line 62

def self.read_type_class type, reference
  warn "#{caller[0]}: read_type_class is deprecated" if $VERBOSE
  _, _, type, name = type.split ':', 4

  reference = name.split('::').inject(reference) do |k,n|
    k.const_get(n.to_sym)
  end if name
  [type, reference]
end

.remove_type(type_tag) ⇒ Object



480
481
482
# File 'lib/psych.rb', line 480

def self.remove_type type_tag
  @domain_types.delete type_tag
end

.safe_load(yaml, whitelist_classes = [], whitelist_symbols = [], aliases = false, filename = nil) ⇒ Object

Safely load the yaml string in yaml. By default, only the following classes are allowed to be deserialized:

  • TrueClass

  • FalseClass

  • NilClass

  • Numeric

  • String

  • Array

  • Hash

Recursive data structures are not allowed by default. Arbitrary classes can be allowed by adding those classes to the whitelist. They are additive. For example, to allow Date deserialization:

Psych.safe_load(yaml, [Date])

Now the Date class can be loaded in addition to the classes listed above.

Aliases can be explicitly allowed by changing the aliases parameter. For example:

x = []
x << x
yaml = Psych.dump x
Psych.safe_load yaml               # => raises an exception
Psych.safe_load yaml, [], [], true # => loads the aliases

A Psych::DisallowedClass exception will be raised if the yaml contains a class that isn't in the whitelist.

A Psych::BadAlias exception will be raised if the yaml contains aliases but the aliases parameter is set to false.



282
283
284
285
286
287
288
289
290
291
292
293
294
295
# File 'lib/psych.rb', line 282

def self.safe_load yaml, whitelist_classes = [], whitelist_symbols = [], aliases = false, filename = nil
  result = parse(yaml, filename)
  return unless result

  class_loader = ClassLoader::Restricted.new(whitelist_classes.map(&:to_s),
                                             whitelist_symbols.map(&:to_s))
  scanner      = ScalarScanner.new class_loader
  if aliases
    visitor = Visitors::ToRuby.new scanner, class_loader
  else
    visitor = Visitors::NoAliasRuby.new scanner, class_loader
  end
  visitor.accept result
end

.tagurize(thing) ⇒ Object



56
57
58
59
60
# File 'lib/psych/deprecated.rb', line 56

def self.tagurize thing
  warn "#{caller[0]}: add_private_type is deprecated, use add_domain_type" if $VERBOSE
  return thing unless String === thing
  "tag:yaml.org,2002:#{thing}"
end

.to_json(object) ⇒ Object

Dump Ruby object to a JSON string.



428
429
430
431
432
# File 'lib/psych.rb', line 428

def self.to_json object
  visitor = Psych::Visitors::JSONTree.create
  visitor << object
  visitor.tree.yaml
end