Felipe Gasper
and 1 contributors

NAME

Net::WAMP - Support for Web Application Messaging Protocol (“WAMP”)

SYNOPSIS

A simple client:

    package My_Client;

    use strict; use warnings;

    #Your client can implement any or all of the following role classes:
    use parent (
        #“Producer” roles:
        'Net::WAMP::Role::Publisher',
        'Net::WAMP::Role::Callee',

        #“Consumer” roles:
        'Net::WAMP::Role::Subscriber',
        'Net::WAMP::Role::Caller',
    );

    #for the Subscriber class
    sub on_EVENT {
        my ($self, $msg_obj, $topic) = @_;
        ...
    }

    #for the Callee class
    sub on_INVOCATION {
        my ($self, $msg_obj, $procedure, $worker_obj) = @_;
        ...
    }

    #----------------------------------------------------------------------

    package main;

    my $client = My_Client->new(
        serialization => 'json',

        #Output this way:
        on_send => sub {
            my $serialized_bytes = shift;
            _send_serialized($serialized_bytes);
        },
    );

    $client->send_HELLO( 'my-realm' );

    #Input this way:
    my $msg = $client->handle_message( _read_from_transport() );

    #Do some sort of validation of the WELCOME message here …

    $client->send_PUBLISH(
        {},
        'com.haha.demo.chat',
        [ 'This is a message.' ],
    );

DESCRIPTION

This distribution provides support in Perl for the Web Application Messaging Protocol (WAMP).

ALPHA STATUS

CAVEAT EMPTOR!

The WAMP standard itself is not yet finalized, so any implementations are by definition subject to change. (The current specification is itself a significant revision of an earlier proposed standard.) That said, the details of it should be pretty stable by this point, so changes should be relatively minor.

Net::WAMP will attempt to accommodate any future updates to the protocol with backward compatibility; however, at this point there are NO guarantees, and you should absolutely check the changelog before updating.

Several of the specification’s “Advanced” features are marked as being in less-than-stable states. This implementation will probably hold off on implementing those as a result; however, pull requests will be considered.

Net::WAMP’s design aims to implement only WAMP and to be agnostic about anything else: which way you do transport, what you do with your messages, etc. As a consequence, its footprint is pretty light, though you’ll likely want for other modules (e.g., Net::WebSocket) to implement transport. This distribution does include an implementation of WAMP’s RawSocket protocol; however, nothing compels you to use this particular implementation. If you wanted to use your own (maybe using XS?), nothing prevents you, and you should have minimal, if any, unused code loaded.

You may get a better sense of how to use Net::WAMP by looking at the distribution’s example scripts; however, for the sake of completeness, here is the formal documentation. The following assumes that you are already familiar with WAMP; consult the specification for more background if you need it.

There have been several internal design changes over the course of development, some of which the documentation may not reflect. Please open tasks for any inconsistencies you note between the documentation and the actual code.

WORKFLOW

The basic workflow is:

0) Define your WAMP role class.
1) Set up your transport layer (e.g., WebSocket).
2) Instantiate your WAMP role class, with the appropriate serialization and on_send callback.
3) WAMP handshake (HELLO/WELCOME)

… then just sending and receiving messages.

ROLE CLASSES

The role classes contain the role-specific logic for packaging and parsing WAMP messages. These are the centerpiece of your WAMP interactions.

Your application should create a subclass of one or more of the provided roles. Use multiple inheritance to govern which roles your subclass will execute. An instance of that subclass defines your application’s WAMP activity. Such a subclass must implement either client or router roles, but NOT both:

Client Roles:

Router Roles:

COMMON METHODS: CLIENTS

Each client class implements the following methods:

CLASS->new( %OPTS )

… with %OPTS being:

  • on_send (required): A coderef that gets called for each message the client will send. This coderef must send this message to whatever transport layer (e.g., WebSocket, RawSocket, …) you’re using.

  • serialization (optional): json is the default; msgpack is also an option.

OBJ->send_HELLO( REALM, AUXILIARY_HR )

Sends a HELLO message to the given REALM. AUXILIARY_HR is optional and, if given, will be merged with the features data for this framework.

OBJ->send_GOODBYE( AUXILIARY_HR, REASON )

OBJ->send_ABORT( AUXILIARY_HR, REASON )

See the WAMP specification for what these do.

OBJ->handle_message( SERIALIZED_MESSAGE )

For each message you receive from your transport layer, send the message payload into this method. For example, if you’re using WebSocket, the WebSocket message’s payload is what this function should receive. This method will convert this raw payload into a message object (i.e., an instance of a subclass of Net::WAMP::Message), which will be handled internally and send to whatever handler your role class might define for that message.

CLIENT SUBCLASS INTERFACE

OBJ->REQUIRE_STRICT_PEER_ROLES()

This method governs whether Net::WAMP will require a peer to disclose its role correctly in order to send a message to it. Not all WAMP implementations advertise roles according to the WAMP specification in their HELLO/WELCOME, so this can be useful for accommodating such libraries.

WRITING A ROUTER

The bad news is: WAMP Routers are more complicated than Clients. They all but guarantee a requirement for multiplexed I/O, and they have to maintain state, manage access control, etc.

The good news is: Net::WAMP takes care of lots of that for you! So once you’ve got your transport set up, Router behavior becomes reasonably straightforward.

Net::WAMP does NOT implement everything you need to build a Router; instead, it implements just the WAMP parts. You can decide for yourself how you want to do things like I/O.

The router workflow is:

1) Accept a new connection.
2) Set up transport with this new connection.
3) Create a Net::WAMP::Session object with the new connection. (The client should have told you by now which serialization it wants.)
4) Now handle_message(), essentially the same as with the Client.

COMMON METHODS: ROUTER

Router methods mirror their client counterparts, but generally with the addition of a Net::WAMP::Session object:

CLASS->new()

Currently this takes no parameters.

OBJ->handle_message( SESSION_OBJ, SERIALIZED_MESSAGE )

Just like its client counterpart, but the SESSION_OBJ tells the Router where the message came from.

OBJ->send_GOODBYE( SESSION_OBJ, AUXILIARY_HR, REASON )

OBJ->send_ABORT( SESSION_OBJ, AUXILIARY_HR, REASON )

See the WAMP specification for what these do.

OBJ->forget_session( SESSION_OBJ )

“Forget”s a session object by removing all traces of it from the Router object internals. You’ll probably only do this when a WAMP session has ended.

ROLE MESSAGE HANDLERS

Each role has specific message types that it receives; for example, a Subscriber receives EVENT messages. If you write a Subscriber application, you’ll probably need to consume these messages. To do this, define an on_EVENT() method. Likewise, a Caller class will probably define an on_RESULT() method, just as a Callee will define on_INVOCATION.

ERROR messages are special: use methods on_ERROR_CALL(), etc.

Most handlers just receive the appropriate Message object (more on these later); see the individual modules’ documentation for variances from that pattern.

Note that Router classes (Dealer and Broker) have a special get_session() method that returns the Session object for the current message.

I/O

To maximize flexibility, Net::WAMP does not read or write directly to filehandles; instead, it accepts serialized messages (via the handle_message() method) and sends serialized messaged to a callback function (on_send).

For example, if you’re doing WAMP over WebSocket, you’ll feed each WebSocket message’s payload into handle_message() and set on_send to write its passed payload to WebSocket.

The expectation is that whatever transport layer you have underneath WAMP—WebSocket, “RawSocket”, or what have you—receives data in the appropriate message chunks already (see IO::Framed for an example) and can “do the needful” with a serialized message to send. This makes it possible to nest WAMP within some other transport mechanism—even another messaging protocol!

WAMP “RawSocket”

Net::WAMP includes a full implementation of WAMP’s “RawSocket” protocol in Net::WAMP::RawSocket. This protocol is simpler than WebSocket and is probably a better choice for communication between any two WAMP nodes that can speak raw TCP.

SERIALIZATIONS

WAMP defines two serializations officially: JSON (json) and MessagePack (msgpack).

Note that MessagePack is a bit inefficient for now owing to some hackery that works around Data::MessagePack’s proprietary boolean logic; hopefully that can go away after a certain pull request. is merged.

BOOLEAN VALUES

Net::WAMP uses Types::Serialiser to represent boolean values. You’ll need to do likewise to interact with Net::WAMP. (Sorry.)

MESSAGE CLASSES

Each message type has its own class. Each class has the following methods:

OBJ->get_type()

e.g., HELLO, PUBLISHED, …

OBJ->get( KEY )

Returns the value of the given key from the message. For all but one case, the key should correspond to a value as given in the message type definition in the protocol specification: for example, HELLO messages’s Realm attribute.

The one exception to this correlation is the Details/Options dictionaries. You’ll notice that the WAMP specification defines either a Details or Options parameter for almost every message type. The logic behind this naming duality is not consistently applied, and the duality serves no practical purpose since no message can have both Options and Details. In my opinion, this is just two names for the same thing, which is just extra terminology to keep track of. For these reasons, Net::WAMP generalizes these names to Auxiliary. If you like, you can still use either of the other names for any of the message types that contains either (i.e., you can use Options with HELLO just the same as Details).

(NB: This may become a permanent change in the protocol specification.)

SPECIFIC MESSAGE CLASSES

Net::WebSocket::Message::PUBLISH

This class has methods publisher_wants_acknowledgement() and publisher_wants_to_be_excluded() to indicate whether the given message expresses these desires. See the WAMP specification’s discussion of this message type and the Publisher Exclusion feature for more details.

Net::WebSocket::Message::CALL

Net::WebSocket::Message::INVOCATION

Both of these have a caller_can_receive_progress() method that returns a boolean to indicate whether the caller indicated a willingness to receive a progressive response to this specific remote procedure call. See the WAMP specification’s discussion of the Progressive Call Results feature feature for more information.

Net::WebSocket::Message::YIELD

Net::WebSocket::Message::RESULT

Both of these have an is_progress() method that returns a boolean to indicate whether this message will be followed by others for the same CALL/INVOCATION. See the WAMP specification’s discussion of the Progressive Call Results feature for more information.

ADVANCED PROFILE FEATURES

Net::WAMP supports a few of WAMP’s Advanced Profile features. More may be added at a later date; patches for at least the reasonably stable features are welcome. :)

TODO

Support more Advanced Profile features, especially:

REPOSITORY

https://github.com/FGasper/p5-Net-WAMP

AUTHOR

Felipe Gasper (FELIPE)

COPYRIGHT

Copyright 2017 by Gasper Software Consulting, LLC

LICENSE

This distribution is released under the same license as Perl.

3 POD Errors

The following errors were encountered while parsing the POD:

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You forgot a '=back' before '=head1'

Around line 369:

You forgot a '=back' before '=head2'

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=back without =over