Braviz Inter Application Communication

Braviz applications can share data because all of them work on the same database. They may also send messages and listen to them. With this mechanism it is possible to coordinate several applications and therefore enrich the analysis environment.

Messages are transmitted over TCP using the 0MQ protocol. The current configuration has a message broker which retransmits messages to all running applications. This broker usually runs on the menu application.

On one side, the broker acts as a publisher, and all applications subscribe to receive messages from it. On the other side it acts as a sink receiving messages from all applications. It has two addresses, one for publishing messages, to which applications should subscribe, and a listening one, to which applications should send messages. These are the only two well known addresses in the network.

The broker is implemented in MessageServer, and the client side is implement in MessageClient. Both of these classes generate PyQt-Signals when they receive a message, and therefore are easy to connect to the rest of your application.

The protocol of the messages themselves is described in Braviz Messages.

Message Broker

class MessageServer(local_only=True)

Acts as a message broker, listens for messages in one port, and broadcasts them in another port

Also generates the message_received signal when it receives a message with the message string. The broadcast and receive addresses are binded to ephimeral ports, use the respective properties to query them.

Parameters:local_only (bool) – If True the server will only accept connections from localhost

broadcast_address

The address in which this server broadcasts messages

pause

Pause the server, received messages will be ignored.

receive_address

The address in which the server listens for messages

send_message(msg)

Send a message in the broadcast address

Parameters:msg (dict) – Message to broadcast, will be encoded as JSON

start_server()

Starts the server thread, called by the constructor

stop_server()

Stops the server thread

Message Client

class MessageClient(server_broadcast=None, server_receive=None)

A client that connects to MessageServer

When it receives a message it emits the message_received signal with the message string.

Parameters:

• server_broadcast (str) – Address of the server broadcast port
• server_receive (str) – Address of the server receive port

connect_to_server()

Connect to the server, called by the constructor

send_message(msg)

Send a message

Parameters:msg (dict) – Message to send to the server, will be encoded as JSON

server_broadcast

The server broadcast address

server_receive

The server receive address

stop()

stop the client

class PassiveMessageClient(server_broadcast=None, server_receive=None)

A client that connects to MessageServer

When it receives a message it keeps it in memory. The last message may be polled using the method get_last_message()

Parameters:

• server_broadcast (str) – Address of the server broadcast port
• server_receive (str) – Address of the server receive port

connect_to_server()

Connect to the server, called by the constructor

get_last_message()

Get the last received message and a consecutive number

Returns:number, message_text; where the number will increase each time a new message arrives

send_message(msg)

Send a message

Parameters:msg (dict) – Message to send to the server

server_broadcast

The server broadcast address

server_receive

The server receive address

stop()

stop the client

class GenericMessageClient(handler, server_broadcast=None, server_receive=None)

A client that connects to MessageServer

When it receives a message it calls handle_new_message on the handler, optionally, if the handler hast the handle_json_message, it will be called with the raw json message as argument.

Parameters:

• handler (object) – Must implement the handle_new_message method.
• server_broadcast (str) – Address of the server broadcast port
• server_receive (str) – Address of the server receive port

connect_to_server()

Connect to the server, called by the constructor

send_json_message(net_msg)

Send a message already encoded as json

Warning

This message will also bounce to the handler, be careful with loops

Parameters:net_msg (str) – Message to send to the server

send_message(msg)

Send a message

Warning

This message will also bounce to the handler, be careful with loops

Parameters:msg (dict) – Message to send to the server

server_broadcast

The server broadcast address

server_receive

The server receive address

stop()

stop the client

Tornado Clients

This classes are meant to be used inside in tornado web servers to send and receive messages to the rest of the system

class MessageHandler(application, request, **kwargs)

Allow querying for messages and sending messages through http

GET requests will receive json data {"count":<n>,"message",<s>} where count is a number

that increases with any new message, and message is the text of the last message.

POST requests allow to send messages. It is required to have a "message" parameter in the request body

class LongPollMessageHandler(application, request, **kwargs)

Allow querying for messages and sending messages through http

GET requests will receive json data {"message",<s>}. This request will not return until a new message is available. (Long poll)

POST requests allow to send messages. It is required to have a "message" parameter in the request body