window.postMessage to sandboxed iframe

[Henning Skoglund]

I'm writing a temperature logger via chrome.usb ANT+ wireless communication. I'm struggeling with sending messages from a window to the sandboxed iframe (with a local script) thats embedded in the window. The reason for sandboxing the in the iframe is that's impossible to run knockoutjs due to CSP.

I've set up a handler in the iframe like suggested in http://developer.chrome.com/apps/app_external.html "Listen for messages"

var messageHandler = function(e) {

   

  console.log('Knockout App got message', e.data);

};

window.addEventListener('message', messageHandler);

When I type "window.postMessage('test','*')" in the <top frame> in developer tools nothing happens. Changing the frame in the drop-down in devtools and typing the same command calls the messageHandler.

I tried to access the .contentWindow property of the iframe, but it gives "DOMException". And accessing .contentDocument gives SecurityError: Blocked a frame with origin "chrome-extension://kbjdachfmhmlnekmflcomjkhijhjkacl" from accessing a cross-origin frame'

Any thoughts?

[PhistucK]

Is there a specific reason you are not using <webview>?

I never tried it, but I heard it has a pretty extensive API.

Regarding posting a message to yourself (same window to the same window), it works for me in a regular web page -

window.addEventListener("message", function (e) { console.log(e.data) }, false)

window.postMessage("hey", "*")

// Outputs hey

☆PhistucK

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[Henning Skoglund]

Seems like webview is more for hosting external web pages, but I just want to host knockoutjs/UI which is loaded locally. I now know why window.postMessage('test','*') doesnt do anything because its referencing the top window which doesnt have a event handler for message. I only need a reference to the window of the iframe (tried window.frames[0] gives "DOMException") without being with limited by security restrictions.

[PhistucK]

I think it (window.frames[0]) should work, this sounds weird. But anyway, top.frames might get you better results, I am not sure.

Note that accessing window.frames[0] might give you an exception, but perhaps window.frames[0].postMessage can succeed regardless of the exception.

☆PhistucK

[Henning Skoglund]

Yes, it works by posting to window.frames[0].postMessage('test','*'). I was confused by the "DOMException" (strange error msg, I would prefer a DOMException object with more info whats going on.). Thank you for the advice.