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Lars Dɪᴇᴄᴋᴏᴡ 迪拉斯

NAME

Data::HAL - Hypertext Application Language resource

VERSION

This document describes Data::HAL version 1.000

SYNOPSIS

    use Data::HAL qw();
    use Data::HAL::Link qw();
    {
        my $hal = Data::HAL->from_json($json_str);
        my $resource_member_data_href = $hal->resource;
        my $links_aref = $hal->links;
        my $embedded_resources_aref = $hal->embedded;
    }

    {
        my $hal = Data::HAL->new(
            resource => {foo => 23, bar => 42},
            links    => [Data::HAL::Link->new(relation => 'self', href => '/')],
        );

        my $json_str = $hal->as_json;
        # {
        #    "_links" : {
        #       "self" : {
        #          "href" : "/"
        #       }
        #    },
        #    "bar" : 42,
        #    "foo" : 23
        # }

        my @headers = $hal->http_headers;
        # (
        #     'Content-Type' => 'application/hal+json',
        #     'Link' => '</>;rel="self"'
        # )
    }

DESCRIPTION

HAL is a format you can use in your hypermedia API.

Introduction

This section is completely quoted from the specification:

There is an emergence of non-HTML HTTP applications ("Web APIs") which use hyperlinks to direct clients around their resources.

The JSON Hypertext Application Language (HAL) is a standard which establishes conventions for expressing hypermedia controls, such as links, with JSON.

HAL is a generic media type with which Web APIs can be developed and exposed as series of links. Clients of these APIs can select links by their link relation type and traverse them in order to progress through the application.

HAL's conventions result in a uniform interface for serving and consuming hypermedia, enabling the creation of general-purpose libraries that can be re-used on any API utilising HAL.

The primary design goals of HAL are generality and simplicity. HAL can be applied to many different domains, and imposes the minimal amount of structure necessary to cover the key requirements of a hypermedia Web API.

Conformance

The author claims to conform with http://tools.ietf.org/html/draft-kelly-json-hal-06, published 2013-10-03.

INTERFACE

Composition

None.

Constructors

from_json

    Data::HAL->from_json($json_str)

Takes a HAL+JSON document as string and returns a Data::HAL object.

new

    Data::HAL->new(
        resource => {foo => 23, bar => 42},
        links    => [Data::HAL::Link->new(relation => 'self', href => '/')]
    )

Default Moo constructor, returns a Data::HAL object.

Attributes

embedded

Type ArrayRef[Data::HAL], embedded resource objects

Type ArrayRef[Data::HAL::Link], link objects

resource

Type HashRef, member data representing the current state of the resource

relation

Type Data::HAL::URI, identifier of the semantics of a link

Perl strings are coerced to the Data::HAL::URI type.

A stand-alone HAL+JSON document, when deserialised, will not have this attribute set in the root resource since nothing is linking to the document.

Methods

TO_JSON

Serialisation hook for the JSON (or compatible) module.

This method is not intended to be called directly from your code. Instead call "as_json" or JSON::to_json $hal, { convert_blessed => 1 } or similar.

as_json

Returns the resource object serialised as a HAL+JSON document string.

http_headers

Returns a list of pairs of HTTP message headers. The keys are field name strings and the values are field content strings. Warning: since field names can repeat, assigning this list to a hash loses information.

The list is suitable as input for e.g. the headers accessor in HTTP::Headers or the headers attribute in Plack::Response.

Content-Type

The value is application/hal+json, perhaps with a profile parameter.

See "as_http_link_value" in Data::HAL::Link.

Exports

None.

DIAGNOSTICS

not a JSON object

The "from_json" constructor throws this exception of type failure::Data::HAL::InvalidJSON when the JSON input is a malformed HAL+JSON document.

CONFIGURATION AND ENVIRONMENT

Requires no configuration files or environment variables.

DEPENDENCIES

See meta file in the source distribution.

INCOMPATIBILITIES

None reported.

BUGS AND LIMITATIONS

Please report any bugs or feature requests to bug-data-hal@rt.cpan.org, or through the web interface at https://rt.cpan.org/Public/Dist/Display.html?Name=Data-HAL.

tight coupling to JSON

It is currently difficult to exert control over the specifics of (de)serialisation, perhaps put the (de)serialisers into attributes?

error type is an attribute, not a class name

It is not worth it to design an error class hierarchy for a single error.

Data::HAL::URI::NamespaceMap is undocumented

It is used only internally.

TO DO

make everything cache-friendly
support §8.3. cache pattern
support HAL XML

SEE ALSO

AtomPub, the more mature, featureful hypermedia protocol

AUTHOR

Lars Dɪᴇᴄᴋᴏᴡ <daxim@cpan.org>

LICENCE AND COPYRIGHT

Copyright © 2013 Lars Dɪᴇᴄᴋᴏᴡ <daxim@cpan.org>

This library is free software; you can redistribute it and/or modify it under the same terms as Perl 5.18.0.

Disclaimer of warranty

This library is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.