STOMP -- a SWI-Prolog STOMP client
Hongxin Liang and Jan Wielemaker
SWI-Prolog Solutions b.v.
The Netherlands
E-mail: jan@swi-prolog.org
Abstract
This package provide a client to STOMP, The Simple Text Oriented Messaging Protocol. See the STOMP specification for details. We used STOMP to connect to the RabbitMQ message broker.

# Table of Contents

## 1 library(stomp): STOMP client.

author
  Hongxin Liang and Jan Wielemaker
See also
  - http://stomp.github.io/index.html
  - https://github.com/jasonrbriggs/stomp.py
license
  BSD-2
To be done
  TSL support

This module provides a STOMP (Simple (or Streaming) Text Orientated Messaging Protocol) client. This client is based on work by Hongxin Liang. The current version is a major rewrite, both changing the API and the low-level STOMP frame (de)serialization.

The predicate stomp_connection/5 is used to register a connection. The connection is established by stomp_connect/1, which is lazily called from any of the predicates that send a STOMP frame. After establishing the connection two threads are created. One receives STOMP frames and the other manages and watches the heart beat.

### 1.1 Threading

Upon receiving a frame the callback registered with stomp_connection/5 is called in the context of the receiving thread. More demanding applications may decide to send incomming frames to a SWI-Prolog message queue and have one or more worker threads processing the input. Alternatively, frames may be inspected by the receiving thread and either processed immediately or be dispatched to either new or running threads. The best scenario depends on the message rate, processing time and concurrency of the Prolog application.

All message sending predicates of this library are thread safe. If two threads send a frame to the same connection the library ensures that both frames are properly serialized.

### 1.2 Reconnecting

By default this library tries to establish the connection and the user gets notified by means of a `disconnected` pseudo frame that the connection is lost. Using the Options argument of stomp_connection/6 the system can be configured to try and keep connecting if the server is not available and reconnect if the connection is lost. See the `pong.pl` example.

[det]stomp_connection(+Address, +Host, +Headers, :Callback, -Connection)
[det]stomp_connection(+Address, +Host, +Headers, :Callback, -Connection, +Options)
  Create a connection reference. The connection is not set up yet by this predicate. Callback is called on any received frame except for heart beat frames as below.

      call(Callback, Command, Connection, Header, Body)

  Where command is one of the commands below. Header is a dict holding the STOMP frame header, where all values are strings except for the `'content-length'` key value which is passed as an integer.

  Body is a string or, if the data is of the type `application/json`, a dict.

  connected
    A connection was established. Connection and Header are valid.
  disconnected
    The connection was lost. Only Connection is valid.
  message
    A message arrived. All three arguments are valid. Body is a dict if the `content-type` of the message is `application/json` and a string otherwise.
  heartbeat
    A heartbeat was received. Only Connection is valid. This callback is also called for each newline that follows a frame. These newlines can be a heartbeat, but can also be additional newlines that follow a frame.
  heartbeat_timeout
    No heartbeat was received. Only Connection is valid.
  error
    An error happened. All three arguments are valid and handled as `message`.

  Note that stomp_teardown/1 causes the receiving and heartbeat thread to be signalled with abort/0.

  Options processed:

  reconnect(+Bool)
    Try to reestablish the connection to the server if the connection is lost. Default is `false`
  connect_timeout(+Seconds)
    Maximum time to try and reestablish a connection. The default is `600` (10 minutes).
  json_options(+Options)
    Options passed to json_read_dict/3 to translate `application/json` content to Prolog. Default is `[]`.

  Address | is a valid address for tcp_connect/3. Normally a term Host:Port, e.g., `localhost:32772`.
  Host | is a path denoting the STOMP host. Often just `/`.
  Headers | is a dict with STOMP headers used for the `CONNECT` request.
  Connection | is an opaque ground term that identifies the connection.

[nondet]stomp_connection_property(?Connection, ?Property)
  True when Property, is a property of Connection. Defined properties are:
  address(Address)
  callback(Callback)
  host(Host)
  headers(Headers)
  reconnect(Bool)
  connect_timeout(Seconds)
    All the above properties result from the stomp_connection/6 registration.
  receiver_thread_id(Thread)
  stream(Stream)
  heartbeat_thread_id(Thread)
  received_heartbeat(TimeStamp)
    These describe an active STOMP connection.
stomp_destroy_connection(+Connection)
  Destroy a connection. If it is active, first use stomp_teardown/1 to disconnect.
[det]stomp_setup(+Connection, +Options)
  Set up the actual socket connection and start receiving thread. This is a no-op if the connection has already been created. The Options processed are below. Other options are passed to tcp_connect/3.
  timeout(+Seconds)
    If tcp_connect/3 fails, retry until the timeout is reached. If Seconds is `inf` or `infinite`, keep retrying forever.
[semidet]stomp_teardown(+Connection)
  Tear down the socket connection, stop receiving thread and heartbeat thread (if applicable). The registration of the connection as created by stomp_connection/5 is preserved and the connection may be reconnected using stomp_connect/1.
[det]stomp_reconnect(+Connection)
  Teardown the connection and try to reconnect.
[det]stomp_connect(+Connection)
[det]stomp_connect(+Connection, +Options)
  Setup the connection. First ensures a socket connection and if this is new send a `CONNECT` frame. Protocol version and heartbeat negotiation will be handled. `STOMP` frame is not used for backward compatibility.

  This predicate waits for the connection handshake to have completed. Currently it waits for a maximum of 10 seconds after establishing the socket for the server reply.

  Calling this on an established connection has no effect.

  Errors
    `stomp_error(connect, Connection, Detail)` if no connection could be established.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#CONNECT_or_STOMP_Frame).
[det]stomp_send(+Connection, +Destination, +Headers, +Body)
  Send a `SEND` frame. If `content-type` is not provided, `text/plain` will be used. `content-length` will be filled in automatically.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#SEND
[det]stomp_send_json(+Connection, +Destination, +Headers, +JSON)
  Send a `SEND` frame. `JSON` can be either a JSON term or a dict. `content-type` is filled in automatically as `application/json` and `content-length` will be filled in automatically as well.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#SEND
[det]stomp_subscribe(+Connection, +Destination, +Id, +Headers)
  Send a `SUBSCRIBE` frame.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#SUBSCRIBE
[det]stomp_unsubscribe(+Connection, +Id)
  Send an `UNSUBSCRIBE` frame.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#UNSUBSCRIBE
[det]stomp_ack(+Connection, +MessageId, +Headers)
  Send an `ACK` frame. See stomp_ack/2 for simply passing the header received with the message we acknowledge.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#ACK
[det]stomp_nack(+Connection, +MessageId, +Headers)
  Send a `NACK` frame. See stomp_nack/2 for simply passing the header received with the message we acknowledge.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#NACK
[det]stomp_ack(+Connection, +MsgHeader)
[det]stomp_nack(+Connection, +MsgHeader)
  Reply with an ACK or NACK based on the received message header. On a STOMP 1.1 request we get an `ack` field in the header and reply with an `id`. For STOMP 1.2 we reply with the `message-id` and `subscription` that we received with the message.
[det]stomp_begin(+Connection, +Transaction)
  Send a `BEGIN` frame. @see http://stomp.github.io/stomp-specification-1.2.html#BEGIN
[det]stomp_commit(+Connection, +Transaction)
  Send a `COMMIT` frame.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#COMMIT
[det]stomp_abort(+Connection, +Transaction)
  Send a `ABORT` frame.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#ABORT
[semidet]stomp_transaction(+Connection, :Goal)
  Run Goal as once/1, tagging all `SEND` messages inside the transaction with the transaction id. If Goal fails or raises an exception the transaction is aborted. Failure or exceptions cause the transaction to be aborted using stomp_abort/2, after which the result is forwarded.
[det]stomp_disconnect(+Connection, +Headers)
  Send a `DISCONNECT` frame. If the connection has the `reconnect` property set to `true`, this will be reset to `disconnected` to avoid reconnecting. A subsequent stomp_connect/2 resets the reconnect status.
  See also
    http://stomp.github.io/stomp-specification-1.2.html#DISCONNECT

# Index

?
stomp_abort/2
stomp_ack/2
stomp_ack/3
stomp_begin/2
stomp_commit/2
stomp_connect/1
stomp_connect/2
stomp_connection/5
stomp_connection/6
stomp_connection_property/2
stomp_destroy_connection/1
stomp_disconnect/2
stomp_nack/2
stomp_nack/3
stomp_reconnect/1
stomp_send/4
stomp_send_json/4
stomp_setup/2
stomp_subscribe/4
stomp_teardown/1
stomp_transaction/2
stomp_unsubscribe/2