Accessing ArrayBuffer or Uint8Array data from a CefV8Value

[Mayhew]

Hi everyone,
I have a web page that I want to have pass an ArrayBuffer or Uint8Array in to my own V8 handler via javascript. The argument in my handlers Execute method shows up as an "object" but I am not sure how to easily access its data. I see an enhancement request for CEF to directly support ArrayBuffer but am wondering if anyone has found another solution in the meantime.

John

[magreenblatt]

ArrayBuffer provides methods and properties for accessing the underlying data: https://developer.mozilla.org/en-US/doc ... rrayBuffer

You should be able to call these methods from your native code using ExecuteFunction, GetValue, etc on the ArrayBuffer "object".

[Mayhew]

I am a bit worried about the overhead of doing a loop and calling ExecuteFunction() to get each element when the array gets large. Would it be any better to just have the web app first copy to a standard javascript array and pass that to me? I still have to loop over the array object and call GetValue(someIndex)->GetUIntValue(); so I'm not sure if that will give me any better performance or not.

[magreenblatt]

If the amount of binary data is large, and you eventually want to use the data in the browser process, then the best option might be to implement a custom scheme handler and have JavaScript send the data via XMLHttpRequest. See for example https://developer.mozilla.org/en-US/doc ... inary_Data.

[tml]

Do you happen to have measurements of how the XHR way you suggested compares with CefProcessMessage? Gut feelings and related insights are also welcome. Actually, I have been trying to measure the throughput of both approaches but so far I haven't seen a huge difference (XHR appears to be a tiny bit slower). Does XHR/resource loading use CefProcessMessage internally?

[magreenblatt]

I have been trying to measure the throughput of both approaches but so far I haven't seen a huge difference (XHR appears to be a tiny bit slower).

That sounds about right. The advantages of XHR is that it's easier to use directly from JavaScript, it won't interfere with other data on the IPC channel (like rendering-related messages), and you don't need to worry about message size limits (approx 128MB for CefProcessMessage including structural overhead).

Does XHR/resource loading use CefProcessMessage internally?

Both network loading and CefProcessMessage use the same underlying IPC channel. There is no special scheduling/prioritization for CefProcessMessage so large messages may interfere with more critical communication.