When using Psych.load to deserialize a YAML document, the document is translated to an intermediary AST. That intermediary AST is then translated in to a Ruby object graph.
In the opposite direction, when using Psych.dump, the Ruby object graph is translated to an intermediary AST which is then converted to a YAML document.
Psych::Nodes contains all of the classes that make up the nodes of a YAML AST. You can manually build an AST and use one of the visitors (see Psych::Visitors) to convert that AST to either a YAML document or to a Ruby object graph.
Here is an example of building an AST that represents a list with one scalar:
# Create our nodes stream = Psych::Nodes::Stream.new doc = Psych::Nodes::Document.new seq = Psych::Nodes::Sequence.new scalar = Psych::Nodes::Scalar.new('foo') # Build up our tree stream.children << doc doc.children << seq seq.children << scalar
The stream is the root of the tree. We can then convert the tree to YAML:
stream.to_yaml => "---\n- foo\n"
Or convert it to Ruby:
stream.to_ruby => [["foo"]]
YAML AST Requirements A valid YAML AST must have one Psych::Nodes::Stream at the root. A Psych::Nodes::Stream node must have 1 or more Psych::Nodes::Document nodes as children.
Psych::Nodes::Document nodes must have one and only one child. That child may be one of:
Psych::Nodes::Sequence and Psych::Nodes::Mapping nodes may have many children, but Psych::Nodes::Mapping nodes should have an even number of children.
All of these are valid children for Psych::Nodes::Sequence and Psych::Nodes::Mapping nodes:
Psych::Nodes::Scalar and Psych::Nodes::Alias are both terminal nodes and should not have any children.
Extends command line arguments array (ARGV) to parse itself.
Acceptable argument classes. Now contains DecimalInteger, OctalInteger and DecimalNumeric. See Acceptable argument classes (in source code).
Module that defines helper methods for pretty_print.
Raised by Encoding and String methods when the source encoding is incompatible with the target encoding.
The base exception for JSON errors.
This exception is raised if the nesting of parsed data structures is too deep.
This class is used as a return value from ObjectSpace::reachable_objects_from.
When ObjectSpace::reachable_objects_from returns an object with references to an internal object, an instance of this class is returned.
You can use the type method to check the type of the internal object.
Configuration for the openssl library.
Many system’s installation of openssl library will depend on your system configuration. See the value of OpenSSL::Config::DEFAULT_CONFIG_FILE for the location of the file for your host.
General error for openssl library configuration files. Including formatting, parsing errors, etc.
Subclasses ‘BadAlias` for backwards compatibility
Socket::AncillaryData represents the ancillary data (control information) used by sendmsg and recvmsg system call. It contains socket family, control message (cmsg) level, cmsg type and cmsg data.
Subclass of Zlib::Error
When zlib returns a Z_NEED_DICT if a preset dictionary is needed at this point.
Used by Zlib::Inflate.inflate and Zlib.inflate
Can be raised by IO operations when IO#timeout= is set.
This class is the base class for Net::HTTP response classes.
Method Net::HTTP.get_response returns an instance of one of the subclasses of Net::HTTPResponse:
Net::HTTP.get_response(uri) # => #<Net::HTTPOK 200 OK readbody=true> Net::HTTP.get_response(hostname, '/nosuch') # => #<Net::HTTPNotFound 404 Not Found readbody=true>
As does method Net::HTTP#request:
req = Net::HTTP::Get.new(uri) Net::HTTP.start(hostname) do |http| http.request(req) end # => #<Net::HTTPOK 200 OK readbody=true>
Class Net::HTTPResponse includes module Net::HTTPHeader, which provides access to response header values via (among others):
Hash-like method [].
Specific reader methods, such as content_type.
Examples:
res = Net::HTTP.get_response(uri) # => #<Net::HTTPOK 200 OK readbody=true> res['Content-Type'] # => "text/html; charset=UTF-8" res.content_type # => "text/html"
Class Net::HTTPResponse has a subclass for each HTTP status code. You can look up the response class for a given code:
Net::HTTPResponse::CODE_TO_OBJ['200'] # => Net::HTTPOK Net::HTTPResponse::CODE_TO_OBJ['400'] # => Net::HTTPBadRequest Net::HTTPResponse::CODE_TO_OBJ['404'] # => Net::HTTPNotFound
And you can retrieve the status code for a response object:
Net::HTTP.get_response(uri).code # => "200" Net::HTTP.get_response(hostname, '/nosuch').code # => "404"
The response subclasses (indentation shows class hierarchy):
Net::HTTPUnknownResponse (for unhandled HTTP extensions).
Net::HTTPContinue (100)
Net::HTTPSwitchProtocol (101)
Net::HTTPProcessing (102)
Net::HTTPEarlyHints (103)
Net::HTTPOK (200)
Net::HTTPCreated (201)
Net::HTTPAccepted (202)
Net::HTTPNoContent (204)
Net::HTTPResetContent (205)
Net::HTTPPartialContent (206)
Net::HTTPMultiStatus (207)
Net::HTTPAlreadyReported (208)
Net::HTTPIMUsed (226)
Net::HTTPMultipleChoices (300)
Net::HTTPFound (302)
Net::HTTPSeeOther (303)
Net::HTTPNotModified (304)
Net::HTTPUseProxy (305)
Net::HTTPBadRequest (400)
Net::HTTPUnauthorized (401)
Net::HTTPPaymentRequired (402)
Net::HTTPForbidden (403)
Net::HTTPNotFound (404)
Net::HTTPNotAcceptable (406)
Net::HTTPRequestTimeOut (408)
Net::HTTPConflict (409)
Net::HTTPGone (410)
Net::HTTPLengthRequired (411)
Net::HTTPLocked (423)
Net::HTTPUpgradeRequired (426)
Net::HTTPTooManyRequests (429)
Net::HTTPNotImplemented (501)
Net::HTTPBadGateway (502)
Net::HTTPGatewayTimeOut (504)
Net::HTTPLoopDetected (508)
Net::HTTPNotExtended (510)
There is also the Net::HTTPBadResponse exception which is raised when there is a protocol error.
Response class for No Content responses (status code 204).
The No Content response indicates that the server successfully processed the request, and is not returning any content.
References:
Response class for Reset Content responses (status code 205).
The Reset Content response indicates that the server successfully processed the request, asks that the client reset its document view, and is not returning any content.
References:
Response class for Found responses (status code 302).
The Found response indicates that the client should look at (browse to) another URL.
References: