Module: Psych

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

Overview

Overview

Psych is a YAML parser and emitter. Psych leverages libyaml [Home page: pyyaml.org/wiki/LibYAML] or [HG repo: bitbucket.org/xi/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.safe_load("--- a")             # => 'a'
Psych.safe_load("---\n - a\n - b")   # => ['a', 'b']
# From a trusted string:
Psych.load("--- !ruby/range\nbegin: 0\nend: 42\nexcl: false\n") # => 0..42

Reading from a file

Psych.safe_load_file("data.yml", permitted_classes: [Date])
Psych.load_file("trusted_database.yml")

Exception handling

begin
  # The second argument changes 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 changes 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

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

parser.parse("---\n - a\n - b")
recorder.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: Handlers, JSON, Nodes, Streaming, Visitors Classes: BadAlias, ClassLoader, Coder, Config, DisallowedClass, Emitter, Exception, Handler, Omap, Parser, ScalarScanner, Set, Stream, SyntaxError, TreeBuilder

Constant Summary collapse

LIBYAML_VERSION =

The version of libyaml Psych is using

Psych.libyaml_version.join('.').freeze
VERSION =

The version of Psych you are using

'4.0.0'
DEFAULT_SNAKEYAML_VERSION =
'1.28'.freeze

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#domain_typesObject

Returns the value of attribute domain_types


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# File 'lib/psych.rb', line 651

def domain_types
  @domain_types
end

#dump_tagsObject

Returns the value of attribute dump_tags


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# File 'lib/psych.rb', line 650

def dump_tags
  @dump_tags
end

#load_tagsObject

Returns the value of attribute load_tags


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# File 'lib/psych.rb', line 649

def load_tags
  @load_tags
end

Class Method Details

.add_builtin_type(type_tag, &block) ⇒ Object


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# File 'lib/psych.rb', line 599

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

:stopdoc:


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# File 'lib/psych.rb', line 593

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_tag(tag, klass) ⇒ Object


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# File 'lib/psych.rb', line 609

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

Currently supported options are:

:indentation

Number of space characters used to indent. Acceptable value should be in 0..9 range, otherwise option is ignored.

Default: 2.

:line_width

Max character to wrap line at.

Default: 0 (meaning “wrap at 81”).

:canonical

Write “canonical” YAML form (very verbose, yet strictly formal).

Default: false.

:header

Write %YAML [version] at the beginning of document.

Default: false.

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)

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# File 'lib/psych.rb', line 504

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"

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# File 'lib/psych.rb', line 521

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


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# File 'ext/psych/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(major);
    list[1] = INT2NUM(minor);
    list[2] = INT2NUM(patch);

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

.load_stream(yaml, filename: nil, fallback: [], **kwargs) ⇒ 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']

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# File 'lib/psych.rb', line 552

def self.load_stream yaml, filename: nil, fallback: [], **kwargs
  result = if block_given?
             parse_stream(yaml, filename: filename) do |node|
               yield node.to_ruby(**kwargs)
             end
           else
             parse_stream(yaml, filename: filename).children.map { |node| node.to_ruby(**kwargs) }
           end

  return fallback if result.is_a?(Array) && result.empty?
  result
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("--- `", filename: "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.


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# File 'lib/psych.rb', line 397

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

  false
end

.parse_file(filename, fallback: false) ⇒ Object

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

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


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# File 'lib/psych.rb', line 409

def self.parse_file filename, fallback: false
  result = File.open filename, 'r:bom|utf-8' do |f|
    parse f, filename: filename
  end
  result || fallback
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("--- `", filename: "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

Raises a TypeError when NilClass is passed.

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


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# File 'lib/psych.rb', line 451

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


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# File 'lib/psych.rb', line 418

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

.remove_type(type_tag) ⇒ Object


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# File 'lib/psych.rb', line 605

def self.remove_type type_tag
  domain_types.delete type_tag
end

.safe_load(yaml, permitted_classes: [], permitted_symbols: [], aliases: false, filename: nil, fallback: nil, symbolize_names: false, freeze: false) ⇒ 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 permitted_classes keyword argument. They are additive. For example, to allow Date deserialization:

Psych.safe_load(yaml, permitted_classes: [Date])

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

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

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

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

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

filename will be used in the exception message if any exception is raised while parsing.

When the optional symbolize_names keyword argument is set to a true value, returns symbols for keys in Hash objects (default: strings).

Psych.safe_load("---\n foo: bar")                         # => {"foo"=>"bar"}
Psych.safe_load("---\n foo: bar", symbolize_names: true)  # => {:foo=>"bar"}

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# File 'lib/psych.rb', line 322

def self.safe_load yaml, permitted_classes: [], permitted_symbols: [], aliases: false, filename: nil, fallback: nil, symbolize_names: false, freeze: false
  result = parse(yaml, filename: filename)
  return fallback unless result

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

.safe_load_file(filename, **kwargs) ⇒ Object Also known as: load_file

Safely loads the document contained in filename. Returns the yaml contained in filename as a Ruby object, or if the file is empty, it returns the specified fallback return value, which defaults to false. See safe_load for options.


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# File 'lib/psych.rb', line 585

def self.safe_load_file filename, **kwargs
  File.open(filename, 'r:bom|utf-8') { |f|
    self.safe_load f, filename: filename, **kwargs
  }
end

.to_json(object) ⇒ Object

Dump Ruby object to a JSON string.


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# File 'lib/psych.rb', line 531

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

.unsafe_load(yaml, filename: nil, fallback: false, symbolize_names: false, freeze: false) ⇒ Object Also known as: load

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. If yaml is empty, it returns the specified fallback return value, which defaults to false.

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

Example:

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

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

When the optional symbolize_names keyword argument is set to a true value, returns symbols for keys in Hash objects (default: strings).

Psych.unsafe_load("---\n foo: bar")                         # => {"foo"=>"bar"}
Psych.unsafe_load("---\n foo: bar", symbolize_names: true)  # => {:foo=>"bar"}

Raises a TypeError when `yaml` parameter is NilClass

NOTE: This method *should not* be used to parse untrusted documents, such as YAML documents that are supplied via user input. Instead, please use the load method or the safe_load method.


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# File 'lib/psych.rb', line 271

def self.unsafe_load yaml, filename: nil, fallback: false, symbolize_names: false, freeze: false
  result = parse(yaml, filename: filename)
  return fallback unless result
  result.to_ruby(symbolize_names: symbolize_names, freeze: freeze)
end

.unsafe_load_file(filename, **kwargs) ⇒ Object

Load the document contained in filename. Returns the yaml contained in filename as a Ruby object, or if the file is empty, it returns the specified fallback return value, which defaults to false.

NOTE: This method *should not* be used to parse untrusted documents, such as YAML documents that are supplied via user input. Instead, please use the safe_load_file method.


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# File 'lib/psych.rb', line 573

def self.unsafe_load_file filename, **kwargs
  File.open(filename, 'r:bom|utf-8') { |f|
    self.unsafe_load f, filename: filename, **kwargs
  }
end

Instance Method Details

#configObject


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# File 'lib/psych.rb', line 643

def config
  Ractor.current[:PsychConfig] ||= Config.new
end