No error handling mechanism provided.

[chpatton013]

Problem description

I'm building a node application that connects to a rosbridge websocket server. I'm supplying data to the application by playing back a log file on the same machine.

I ran into the following problem with one bag file:

SyntaxError: Unexpected end of JSON input
    at WebSocket.onMessage (.../app/node_modules/roslib/src/core/SocketAdapter.js:104:28)
    at WebSocket.onMessage (.../app/node_modules/ws/lib/WebSocket.js:418:14)
    at emitTwo (events.js:106:13)
    at WebSocket.emit (events.js:191:7)
    at Receiver.ontext (.../app/node_modules/ws/lib/WebSocket.js:816:10)
    at .../app/node_modules/ws/lib/Receiver.js:477:18
    at Receiver.applyExtensions (.../app/node_modules/ws/lib/Receiver.js:364:5)
    at .../app/node_modules/ws/lib/Receiver.js:466:14
    at Receiver.flush (.../app/node_modules/ws/lib/Receiver.js:340:3)
    at Receiver.finish (.../app/node_modules/ws/lib/Receiver.js:482:12)

The error occurs within roslibjs at this line.

The JSON parse is failing because rosbridge sent malformed data. I believe this happened because the bag file has one or more corrupted messages. However, this could also happen in real-world situations if we were to approach our network-bandwidth- or compute-budgets.

Using a top-level exception handler to capture this failure is not a great solution because:

• we have to infer the context for the failure based on the error message in the exception
• we don't know what state any part of the system is left in
• we end up catching errors that shouldn't be caught
• the only safe thing to do at this point is terminate the process

A single corrupted message is not a good enough reason to crash an entire application.

Feature request

roslibjs should provide a means to attach error callbacks for failures to parse incoming messages. You should be able to attach three different types of error callback:

• a subscriber-level basis (provided as another parameter to subscribe)
• a global callback that is invoked for any error that does not have a subscriber-level callback
• a global callback that is invoked for all errors, even if they have a subscriber-level callback

[chpatton013]

Bump

[jihoonl]

I will be happy to accept a pull request for new feature :)