Developer tools student project

Expand the developer tools implementation

Background information: Firefox supports remote developer tools - ie. communicating with an arbitrary server that implements a protocol for exposing information about web content. Servo implements a very basic developer tools server that currently supports executing JS remotely and investigating the DOM tree in the document inspector. We want to expand these capabilities by allowing remote modification of the DOM tree, better JS console integration (exposing historical and real-time exceptions), and enabling server->client messages that are not responses to client->server messages.

Initial step: Build Servo, run it on a webpage with the --devtools argument, connect to it from a recent version of Firefox (see docs about configuring Firefox for this), and experiment with the document inspector and web consoles. Quit Servo and note that it hangs; fix this by sending a ServerExitMsg in constellation.rs inside handle_exit (look at the members of Constellation to find the proper channel for communicating with the devtools). In addition, store a list of accepted connections in the main devtools server code (look for the code that spawns a task to handle the new stream), and close all of the connections right before exiting. Rebuild, run the devtools server and connect to it again, then watch it quit successfully.

• Make the constellation send the devtools server the ServerExitMsg on shutdown
• Make the main devtools loop in devtools/lib.rs store a vector of all accepted connection streams. Before exiting, iterate over the connections and close them.
• Move all devtools-related event handling from script_task.rs into a separate devtools.rs
• Implement the modifyAttributes client->server message that updates the attribute names and values for a DOM node (add a handler in the devtools inspector actor; make it send a message to the script task; have the script task handle it appropriately)
• Make Console::Log cause a message to be sent to the devtools server. This will require finding the window that owns the console object, and using its page to send a message on the devtools channel.
• Make the getCachedMessages message synchronously fetch (nonexistent) cached messages from the script task
• Create a new JS error reporter that logs the error (e.g.) and notifies the script task about the error (use JS_GetGlobalObject and global_object_for_js_object to get access to the right Window to reach the script task)
• Make the script task recognize when to buffer messages and when to send them directly to devtools (use the startListeners/stopListeners messages from Firefox to trigger this behaviour)
• Add support for separated client reading and writing - create a hashtable of pipeline IDs to actor names, and store a clone of the TCPStream in the console actor
• Implement the consoleAPICall message from server->client when a JS error is reported from the script task. When a message arrives with a pipeline ID, find the tab actor in the hashtable, get the console actor, and have it send a message to the client with the error details.