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builder.cr
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builder.cr
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# A YAML builder generates valid YAML.
#
# A `YAML::Error` is raised if attempting to generate
# an invalid YAML (for example, if invoking `end_sequence`
# without a matching `start_sequence`)
#
# ```
# require "yaml"
#
# string = YAML.build do |yaml|
# yaml.mapping do
# yaml.scalar "foo"
# yaml.sequence do
# yaml.scalar 1
# yaml.scalar 2
# end
# yaml.scalar "bar"
# yaml.mapping do
# yaml.scalar "baz"
# yaml.scalar "qux"
# end
# end
# end
# string # => "---\nfoo:\n- 1\n- 2\nbar:\n baz: qux\n"
# ```
class YAML::Builder
@box : Void*
# By default the maximum nesting of sequences/mappings is 99. Nesting more
# than this will result in a YAML::Error. Changing the value of this property
# allows more/less nesting.
property max_nesting = 99
# Creates a `YAML::Builder` that will write to the given `IO`.
def initialize(@io : IO)
@box = Box.box(io)
@emitter = Pointer(Void).malloc(LibYAML::EMITTER_SIZE).as(LibYAML::Emitter*)
@event = LibYAML::Event.new
@closed = false
@nesting = 0
LibYAML.yaml_emitter_initialize(@emitter)
LibYAML.yaml_emitter_set_unicode(@emitter, 1)
LibYAML.yaml_emitter_set_output(@emitter, ->(data, buffer, size) {
data_io = Box(IO).unbox(data)
data_io.write(Slice.new(buffer, size))
1
}, @box)
end
# Creates a `YAML::Builder` that writes to *io* and yields it to the block.
#
# After returning from the block the builder is closed.
def self.build(io : IO, & : self ->) : Nil
builder = new(io)
yield builder ensure builder.close
end
# Starts a YAML stream.
def start_stream
emit stream_start, LibYAML::Encoding::UTF8
end
# Ends a YAML stream.
def end_stream
emit stream_end
flush
end
# Starts a YAML stream, invokes the block, and ends it.
def stream
start_stream
yield.tap { end_stream }
end
# Starts a document.
def start_document
emit document_start, nil, nil, nil, 0
end
# Ends a document.
def end_document
emit document_end, 1
end
# Starts a document, invokes the block, and then ends it.
def document
start_document
yield.tap { end_document }
end
# Emits a scalar value.
def scalar(value, anchor : String? = nil, tag : String? = nil, style : YAML::ScalarStyle = YAML::ScalarStyle::ANY)
string = value.to_s
implicit = tag ? 0 : 1
emit scalar, get_anchor(anchor), string_to_unsafe(tag), string, string.bytesize, implicit, implicit, style
end
# Starts a sequence.
def start_sequence(anchor : String? = nil, tag : String? = nil, style : YAML::SequenceStyle = YAML::SequenceStyle::ANY)
implicit = tag ? 0 : 1
emit sequence_start, get_anchor(anchor), string_to_unsafe(tag), implicit, style
increase_nesting
end
# Ends a sequence.
def end_sequence
emit sequence_end
decrease_nesting
end
# Starts a sequence, invokes the block, and the ends it.
def sequence(anchor : String? = nil, tag : String? = nil, style : YAML::SequenceStyle = YAML::SequenceStyle::ANY)
start_sequence(anchor, tag, style)
yield.tap { end_sequence }
end
# Starts a mapping.
def start_mapping(anchor : String? = nil, tag : String? = nil, style : YAML::MappingStyle = YAML::MappingStyle::ANY)
implicit = tag ? 0 : 1
emit mapping_start, get_anchor(anchor), string_to_unsafe(tag), implicit, style
increase_nesting
end
# Ends a mapping.
def end_mapping
emit mapping_end
decrease_nesting
end
# Starts a mapping, invokes the block, and then ends it.
def mapping(anchor : String? = nil, tag : String? = nil, style : YAML::MappingStyle = YAML::MappingStyle::ANY)
start_mapping(anchor, tag, style)
yield.tap { end_mapping }
end
# Emits an alias to the given *anchor*.
#
# ```
# require "yaml"
#
# yaml = YAML.build do |builder|
# builder.mapping do
# builder.scalar "key"
# builder.alias "example"
# end
# end
#
# yaml # => "---\nkey: *example\n"
# ```
def alias(anchor : String) : Nil
LibYAML.yaml_alias_event_initialize(pointerof(@event), anchor)
yaml_emit("alias")
end
# Emits the scalar `"<<"` followed by an alias to the given *anchor*.
#
# See [YAML Merge](https://yaml.org/type/merge.html).
#
# ```
# require "yaml"
#
# yaml = YAML.build do |builder|
# builder.mapping do
# builder.merge "development"
# end
# end
#
# yaml # => "---\n<<: *development\n"
# ```
def merge(anchor : String) : Nil
self.scalar "<<"
self.alias anchor
end
# Flushes any pending data to the underlying `IO`.
def flush
LibYAML.yaml_emitter_flush(@emitter)
@io.flush
end
def finalize
return if @closed
LibYAML.yaml_emitter_delete(@emitter)
end
# Closes the builder, freeing up resources.
def close
finalize
@closed = true
end
private def get_anchor(anchor)
string_to_unsafe(anchor)
end
private def string_to_unsafe(tag)
tag.try(&.to_unsafe) || Pointer(UInt8).null
end
private macro emit(event_name, *args)
LibYAML.yaml_{{event_name}}_event_initialize(pointerof(@event), {{*args}})
yaml_emit({{event_name.stringify}})
end
private def yaml_emit(event_name)
ret = LibYAML.yaml_emitter_emit(@emitter, pointerof(@event))
if ret != 1
raise YAML::Error.new("Error emitting #{event_name}")
end
end
private def increase_nesting
@nesting += 1
if @nesting > @max_nesting
raise YAML::Error.new("Nesting of #{@nesting} is too deep")
end
end
private def decrease_nesting
@nesting -= 1
end
end
module YAML
# Returns the resulting String of writing YAML to the yielded `YAML::Builder`.
#
# ```
# require "yaml"
#
# string = YAML.build do |yaml|
# yaml.mapping do
# yaml.scalar "foo"
# yaml.sequence do
# yaml.scalar 1
# yaml.scalar 2
# end
# end
# end
# string # => "---\nfoo:\n- 1\n- 2\n"
# ```
def self.build
String.build do |str|
build(str) do |yaml|
yield yaml
end
end
end
# Writes YAML into the given `IO`. A `YAML::Builder` is yielded to the block.
def self.build(io : IO) : Nil
YAML::Builder.build(io) do |yaml|
yaml.stream do
yaml.document do
yield yaml
end
end
end
end
end