Question

Trying to use TCP sockets using chrome.socket API on Chrome Version 25.0.1364.5 dev.

Looking at the documentation for the chrome.socket.read there doesn’t seem to be a way to get a notification when new data is available to be read.

There is some sample code for a TCP server which polls the read command every 500ms but I think this would not be efficient / accurate

// Start polling for reads.
setInterval(this._periodicallyRead.bind(this, socketId), 500);

What’s more confusing is that in the ‘Network Communications’ Documentation under section ‘Receiving data’, it is stated that a special handler can be passed as an onEvent option in chrome.socket.create

The parameter is an object with one value ‘onEvent’ that is a function reference to the method that will be called when data is available on the port.

This onEvent parameter would be used like this

chrome.socket.create(
    'udp', '127.0.0.1', 1337, 
    { onEvent: handleDataEvent }, // <-- call this when new data is available
    createHandler
)

But this appears to apply only for UDP connections as I get the following error when I try to use it

Error: Invocation of form 
       socket.create(string, string, integer, object, function) 
       doesn't match definition 
       socket.create(string type, optional object options, function callback)

        at Object.normalizeArgumentsAndValidate (schemaUtils:119:11)
        at Object.<anonymous> (schema_generated_bindings:301:32)
        at chrome-extension://obljaojhdffbpcdfbeoiejegaodfoonp/background.js:11:15
        at chrome.Event.dispatchToListener (event_bindings:387:21)
        at chrome.Event.dispatch_ (event_bindings:373:27)
        at dispatchArgs (event_bindings:249:22)
        at Object.app.runtime.onLaunched (app.runtime:116:7)
        at Object.chromeHidden.Event.dispatchEvent (event_bindings:255:35) 

So the question is, can something like this be achieved with TCP Connections ? Instead of having to poll the read method every x milliseconds ?

Update

This is a workaround I am using until better documentation / event support exists.

function onReadHandler(readInfo) {
     // do things with data
     // ....

     // re register handler with callback itself
     chrome.socket.read(socketId,null,onReadHandler);         
}

chrome.socket.read(socketId,null,onReadHandler);

Answer 1

For TCP connections, the callback passed to socket.read will only be executed when there is new data available. The sample code mentioned was fixed to only use the callback instead of the setInterval.

The Network documentation is indeed outdated and we are working hard to update it. If you want to avoid the risk of outdated docs during these days of quickly changing APIs, you should always check the API reference docs – those are generated directly from the code and don’t need editorial work. If you are feeling “hacky” 🙂 you can also look directly at the Chromium source code API definitions (this one is for the socket API)

Last, but not least, for Sublime Text users, there is a Sublime Chrome Apps and Extensions plugin. It’s not finished yet, but you can already get code completion, CSP validation and some boilerplates for bootstrapping. Install it through the Sublime Package Manager.