# ABSTRACT: Rinci access protocol
# PODNAME: Riap

__END__

=pod

=encoding UTF-8

=head1 NAME

Riap - Rinci access protocol

=head1 VERSION

This document describes version 1.2.4 of Riap (from Perl distribution Riap), released on 2015-09-04.

=head1 SYNOPSIS

This document specifies a simple, extensible, client/server, request/response
protocol for requesting metadata and performing actions on code entities.

Examples are written in JSON (sometimes with added comments), but data
structures can actually be encoded using other formats.

=head1 DESCRIPTION

Rinci access protocol (Riap for short), is a client/server, request/response
protocol for requesting metadata and performing actions on code entities. It is
modeled closely after HTTP, but is a different protocol. It can be layered on
top of HTTP (as its transport protocol) but can also use other transports,
including direct TCP.

The server side is viewed as being a tree of code entities, with a package
entity at the root. Other entities (such as subpackages, functions, variables)
are discoverable by performing C<list> actions on package entities. Entity's
metadata can be retrieved using the C<meta> action. There are other actions
defined in the specification; and the protocol can be extended by introducing
more actions.

One of the main use-cases of this protocol is to provide self-descriptive,
self-documenting, machine-discoverable API service, much like the goal of SOAP
and WSDL. However it is much simpler and programmer-friendly than those
protocols.

=head1 SPECIFICATION VERSION

 1.2

=head1 STATUS

The 1.2 series does not guarantee full backward compatibility between revisions,
so caveat implementor. However, major incompatibility will bump the version to
1.3 or 2.0.

=head1 TERMINOLOGIES

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in RFC 2119.

=over 4

=item * Server

=item * Client

=item * Response

Response is an enveloped result as defined in the L<Rinci::function>
specification.

=item * Request

A Riap request is modelled after HTTP request. It consists of an action
(analogous to HTTP request method), code entity URI, protocol version, and zero
or more extra arguments (analogous to HTTP headers). Some extra arguments might
be required, depending on the action.

For simplicity, the request can be expressed as a hash (or dictionary) of
key/value pairs. There should at least be these keys: C<action>, C<uri>, and
C<v> (for protocol version). This also means the extra arguments cannot have
those names. They must also start with letters or underscores followed by zero
or more letters/underscores/digits.

Server should return 400 status if required keys are missing, unknown keys are
sent, or keys contain invalid values.

=back

=head1 RIAP URI SCHEMES

To refer to code entities on the Riap server, a new URI scheme C<riap> is
defined. The URI path describes path to code entities while the URI host
describes the host language. Examples:

 # refer to Text::sprintfn Perl module
 riap://perl/Text/sprintfn/

 # refer to sprintf function in Text::sprintfn Perl module
 riap://perl/Text/sprintfn/sprintfn

 # refer to PHP variable
 riap://php/$var

 # UNDECIDED: refer to class metadata
 riap://perl/My/Class/:class

 # UNDECIDED: refer to distribution metadata
 riap://perl/My/Dist/:distribution

There are some other schemes recognized.

B<pl>. The C<pl> hostless scheme refers to code entities in Perl. This is
preferred in many L<Perinci> modules because the C<riap> scheme is more verbose.
Examples:

 # refer to Text::sprintfn Perl module
 pl:/Text/sprintfn/

 # refer to sprintf function in Text::sprintfn Perl module
 pl:/Text/sprintfn/sprintfn

B<riap+tcp>. This scheme is for L<Riap::Simple> over TCP socket. The host
(+port) part describes TCP host (+port), and the path part describes path to
code entity. Currently there is no default port so please always specify port
number. Examples:

 riap+tcp://localhost:5000/Text/sprintfn/
 riap+tcp://localhost:5000/Text/sprintfn/sprintfn

B<riap+unix>. This scheme is for Riap::Simple over Unix socket. There is no host
part (Unix socket is localhost-only). The path part describes path to the socket
and path to code entity (separated by C<//>).

 riap+unix:/path/to/unix/socket
 riap+unix:/path/to/unix/socket//Text/sprintfn/sprintfn

B<riap+pipe>. This scheme is for Riap::Simple over pipe, to refer to starting a
program and talking the protocol over the pipe. There is no host. The path part
describes path to program, C<//> separator, arguments separated by C</>,
C<//separator>, and path to code entity.

 # refer to accessing code entity via executing "/path/to/program"
 riap+pipe:/path/to/program////Text/sprintfn/sprintfn

 # refer to via accessing code entity via executing "/path/to/program arg1 arg2"
 riap+pipe:/path/to/program//arg1/arg2//Text/sprintfn/sprintfn

=head1 RIAP OVER HTTP/HTTPS

For Riap over HTTP/HTTPS as the transport layer, the standard URI scheme
B<http>/B<https> is used. The URI path for these do not necessarily map directly
to code entities like in C<riap> or C<pl> URIs, they may also support additional
features, as each service provider can choose custom URL layout. Example:

 # access tax::id::validate_npwp function, call with arguments
 http://gudangapi.com/ga/tax.id.npwp/validate_npwp?npwp=123456

 # namespace/module can also be omitted when function name is unique. arguments
 # can also be specified by position
 http://gudangapi.com/ga/validate_npwp/123456

However, any Riap request and any code entity URI can still be requested from
any http/https URL following the L<Riap::HTTP> protocol..

=head1 THE REQUEST

As mentioned previously, the Riap request is a mapping of request keys and their
values. Common request keys:

=over 4

=item * v => FLOAT

Specify Riap protocol version. If not specified, default is C<1.1>. Server
should return 501 status if it does not support requested protocol version.

=item * uri => STR

Required. Specify the location to code entity. It is either a schemeless URI
(e.g. C</Package/SubPackage/func>) to refer to "local" code entity or URI with a
scheme to refer to a remote entity, e.g. C<http://example.org/api/Foo/Bar/func>,
in which case the server can decide to proxy it for the client or not.

The server should return 404 status if B<uri> does not map to an existing code
entity, or 403 if C<uri> is forbidden.

=item * action => STR

Required. Specify action to perform on the code entity.

The server should return 501 status if an action is unknown for the specified
URI. The server should return 401/403 status if authentication is required or
action is not allowed for the specified code entity, respectively.

=item * tx_id => STR

Optional. Transaction ID. Only needed if you want to execute request inside
transaction scope. See L<Riap::Transaction> for more details.

=back

Additional keys might be recognized and/or required according to the action.

=head1 COMMON ACTIONS

Below are the actions which can be implemented by the server. Server can choose
to not implement any action, or implement additional actions. But for actions
mentioned below, the specification must be followed.

=head2 Action: B<info>

Get general information and information about the code entity. This action
requires no additional request keys. Upon success, the server must return a hash
result with at least the following keys (remember that the result is actually
enveloped with a 200 status):

 [200,"OK",
  {
   // entity's type
   "type": "function",

   // canonical URI for the entity
   "uri": "/Package/SubPkg/",
  },
  {"riap.v": 1.2}
 ]

Server may add additional information keys.

=head2 Action: B<actions>

List available actions for code entity. The server should return a list of
action names:

 [200,"OK",
  ["info","actions","meta","call","complete_arg_val"],
  {"riap.v":1.2}
 ]

Additional request key: B<detail> (bool, optional, default false, can be set to
true to make server return a list of records instead).

Under B<detail>, server should return something like this:

 [200,"OK",
  [
   {"name":"info", "summary":"Get general information about code entity"},
   {"name":"actions","summary":"List available actions for code entity"},
   {"name":"meta","summary":"Get metadata for code entity"},
   {"name":"call","summary":"Call function"},
   {"name":"complete_arg_val","summary":"Complete function's argument value"}
  ],
  {"riap.v":1.2}
 ]

It can return additional field like C<keys> to explain additional
required/optional request keys (XXX not yet specified).

=head2 Action: B<meta>

Return Rinci metadata for the code entity. When the entity does not have
metadata, server should return 404 status or better yet 534 (metadata not
found).

=head1 ACTIONS FOR C<package> ENTITIES

Below are actions that must be supported by the C<package> entities.

=head2 Action: B<list>

List entities contained in this package. Additional request keys are: B<type>
(string, optional, to limit only listing entities of a certain type; default is
undef which means list all kinds of entities), B<recursive> (bool, optional, can
be set to true to search subpackages; default is false which means only list
entities in this namespace), B<q> (string, search terms, to only return matching
some search terms; default is undef which means return all entities), B<detail>
(bool, optional, whether to return just a list of code entity URIs or a detailed
record for each entry, defaults to false; if true, then server must return info
hash for each entry, where each info hash like that returned by the C<info>
action).

The server should return 200 status or 206 if partial list is returned. If
B<detail> is true, for each entry a hash must be returned containing at least
B<uri> and B<type>. Server may add additional information like B<summary>,
B<description>, etc.

Example, a C<list> action on the top namespace C</> might return the following:

 [200,"OK",
  ["Math/","Utils/"],
  {"riap.v":1.2}
 ]

Another example, a C<list> action on the C<pl:/Math> namespace, with C<type>
set to C<function> and C<q> to C<multiply>, and C<detail> set to true:

 [200,"OK",
  [
   {"uri": "multiply2",
    "type": "function",
    "summary": "Multiply two numbers"},

   {"uri": "multmany",
    "type": "function",
    "summary": "Multiply several numbers"}
  ],
  {"riap.v":1.2}
 ]

An C<abs_uri> can also be provided by server for each record.

=head2 Action: B<child_metas>

Get metadata for all the children entities of the package entity.

This action can reduce the number of round-trips, as opposed to client
performing C<list> action followed by C<meta> for each child.

Example, an C<child_metas> action on the top namespace C</> might return the
following:

 [200,"OK",
  {
   "Math/":  {"v":1.1, "summary":"This is metadata for Math"},
  ,"Utils/": {"v":1.1, "summary":"This is metadata for Utils"}
  },
  {"riap.v":1.2}
 ]

=head1 ACTIONS FOR C<function> ENTITIES

Below are actions that are available for the C<function> entities. At least
C<call> must be implemented by the server.

=head2 Action: B<call>

Call a function and return its result. Additional request keys include:

=over 4

=item * B<args>

Hash, optional, function arguments, defaults to C<{}>.

In general, do not pass special arguments (arguments prefixed by dash C<->) as
they might be stripped/removed prior to processing. Some special arguments can
be passed through other means (e.g. see C<confirm> and C<dry_run> below).

=item * B<confirm> => BOOL

Optional. If set to true, will pass special argument C<< -confirm => 1 >> to
function. This is used as confirmation when function can return status 331
(requires confirmation). See L<Rinci::function> for more details on status 331.

=item * B<dry_run> => BOOL

Optional. If set to true, will either pass C<< -dry_run => 1 >> to function
supporting dry run, or C<< -tx_action => 'check_state' >> to function supporting
transaction (can more or less be regarded as the dry run equivalent).

=item * B<arg_len> => int

Will be passed to function as special argument C<-arg_len> to send partial
argument value.

=item * B<arg_part_start> => int

Will be passed to function as special argument C<-arg_part_start> to send
partial argument value.

=item * B<art_part_len> => int

Will be passed to function as special argument C<-arg_part_len> to send partial
argument value.

=item * B<res_part_start> => int

Will be passed to function as special argument C<-res_part_start> to request
partial result.

=item * B<res_part_len> => int

Will be passed to function as special argument C<-res_part_len> to request
partial result.

=item * B<stream_arg> => bool

Optional. If set to true, then will provide a filehandle or an iterable object
as argument value for the function, where the function can read data from. And
will also send special argument C<< -arg_stream => 1 >> to function. Note that
the function must have exactly a single argument that has its C<streaming>
property set to true. Otherwise, server MUST send 501 (unimplemented) response.

=back

=head2 Action: B<complete_arg_val>

Complete function argument value, a la Bash tab completion where you have a
semicompleted word and request possible values started by that word. Additional
Riap request keys include:

=over 4

=item * B<arg>

String, required, the name of function argument to complete.

=item * B<word>

String, optional, word that needs to be completed. Defaults to empty string.

=back

The server should return a list of possible completions. Example, when
completing a C<delete_user> function for the argument C<username>, and C<word>
is "st", the server might return:

 [200,"OK",
  ["stella","steven","stuart"],
  {"riap.v":1.2}
 ]

When there is no completion, the server should return an empty list:

 [200,"OK",
  [],
  {"riap.v":1.2}
 ]

=head2 Action: B<complete_arg_elem>

This is just like C<complete_arg_val>, except this tries to complete the value
of an element of an array argument, instead of the value of the argument itself.
This is useful for example when completing this command-line:

 % somecmd --category foo --category <tab>

where C<category> is argument of type array and its element contain some
restricted value. The command-line option C<--category> can be specified
multiple times to set the array elements.

=over 4

=item * B<arg>

String, required, the name of function argument to complete.

=item * B<index>

Integer, required, which element to complete for (starts from 0 for the first
element).

=item * B<word>

String, optional, word that needs to be completed. Defaults to empty string.

=back

=head1 ACTIONS FOR C<variable> ENTITIES

Below are actions that are available for the C<variable> entities.

=head2 Action: B<get>

Get variable value.

=head1 FAQ

=head2 Why no actions to modify metadata/code entities?

Since the specification is extensible by adding more actions, you can implement
this on your system. These actions are not specified by this specification
because currently the main goal of the protocol is to provide API service and
read-only access to the metadata.

Alternatively, modifying metada/code entities can be implemented using calls to
functions on the server which can perform the modifications.

There are also some issues which need to be considered when adding these
actions. First of all, security. Second, you need to decide whether to modify
the running/in-memory copy or the actual source code/files (as the code entities
are usually stored as). When modifying the in-memory copy, the server-side
architecture may have multiple copies (multiple processes and machines). Do you
want to modify all those copies or just one the one process?

=head2 The name?

B<Riap> stands for Rinci access protocol, but it is also an Indonesian word
meaning: to gain in size or number.

=head1 THE RESPONSE

Server must return an enveloped response as specified in L<Rinci::function>
specification, namely a 4-element array: C<< [STATUS, MESSAGE, RESULT, META] >>.
C<STATUS> is an integer, C<MESSAGE> is a string, C<RESULT> is of any type and is
the actual result, and C<META> is a hash.

Starting from Riap 1.2, server must return C<META> which contains at least
C<riap.v> key, containing the Riap protocol version. Client must recognize and
remove all C<riap.*> keys from the response before returning the final result to
user. If there is an unknown C<riap.*> keys or an unrecognized value, it must
fail by returning 501 status to user. This is to handle/detect
incompatibilities/new features in future versions.

=head1 HISTORY

=head2 1.2 (Oct 2014)

Version bumped to 1.2. This version addresses sending/receiving binary data over
JSON. In this version, client can send base64-encoded binary data in arguments
using C<ARGNAME:base64> key. Server can return base64-encoded binary data in
result, this is hinted by the C<riap.result_encoding> attribute in result
medatata. To detect/handle incompatibilities in future versions, client now must
check C<riap.v> and all C<riap.*> properties in result metadata, and fail if it
can't recognize an attribute.

=head2 1.1 (Jan 2012)

Rename specification to Riap. Version bumped to 1.1 to various
backward-incompatible adjustments to Rinci's terminologies.

=head2 1.0 (Aug 2011)

Split specification to L<Sub::Spec::HTTP>.

=head2 May 2011

First release of L<Sub::Spec::HTTP::Server>.

=head1 SEE ALSO

L<Rinci>

JSON RPC, (version 1 at L<http://json-rpc.org>, version 2 at
L<http://jsonrpc.org>). First developed 2005, major revision to version 2 in
2009. Similar to Riap in several aspects: 1) request and response are a single
hash (JSON objects); 2) transport-independent. Differences to Riap: 1) JSON RPC
has a narrower scope, it only deals with RPC/method calls and the other things
like metadata access/exchange, etc; 2) JSON RPC is tied to the JSON format,
while Riap is serialization-format-independent; 3) JSON RPC mandates a request
ID ("id") on every request, to allow pipelining (i.e. client sends an array of
requests at once, answers will come potentially out of order). This could be
added later to the Riap protocol when necessary.

SPORE,
L<https://github.com/SPORE/specifications/blob/master/spore_description.pod>.

B<SOAP, WSDL>. Popular in the early 2000's, with similar goals (easier service
discovery, "simple" request/response protocol which can utilize HTTP or other
transport layer). Fell out of favor along with the rise of JavaScript and REST
and increased criticism against the complexity of XML. Which is ironic because
SOAP was originally created to be the simpler alternative to CORBA.

B<CORBA>.

=head1 HOMEPAGE

Please visit the project's homepage at L<https://metacpan.org/release/Riap>.

=head1 SOURCE

Source repository is at L<https://github.com/perlancar/perl-Riap>.

=head1 BUGS

Please report any bugs or feature requests on the bugtracker website L<https://rt.cpan.org/Public/Dist/Display.html?Name=Riap>

When submitting a bug or request, please include a test-file or a
patch to an existing test-file that illustrates the bug or desired
feature.

=head1 AUTHOR

perlancar <perlancar@cpan.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2015 by perlancar@cpan.org.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut