[Bridge] Array Buffers / Typed Arrays for WebSockets, Ajax

[phoboslab]

It's currently not possible to send/received ArrayBuffers with React Native.

Am I right to assume that this is largely due to the missing TypedArray implementation in JSC? I.e. we're not able to transfer raw memory in a sane and performant way between JavaScript and native.

I've opened an issue over at webkit.org (https://bugs.webkit.org/show_bug.cgi?id=120112), asking for a TypedArray API a few years ago and have written a working implementation for this API (https://github.com/phoboslab/JavaScriptCore-iOS/blob/master/JavaScriptCore/JSTypedArray.h) in my fork of JSC. Forking JSC has worked okay-ish for my own library, but now I'm stumbling over this issue again with React Native.

It would be really useful to be able to load and handle binary data for a number of use cases. So I'm wondering if you guys would be interested to weigh in on a TypedArray API or if you have any ideas how this would be workaroundable without the huge performance penalty that we currently face.

[ide]

There are two roadblocks here. One is the API limitation you described and one solution would be to work with the WebKit team to patch the API for the next-next release of JSC.

The second issue is that the RN bridge uses JSON to communicate between JS and native. There are no shared references so you currently can't access a TypedArray from Obj-C that JS can also access. This could change at the cost of losing the Chrome debugger but if shared memory enables another class of apps that do photo processing, etc, that might be the right trade off.

[vkurchatkin]

We can have a separate ArrayBuffer implementation that is just a handle for raw memory. They can be produced and consumed by some APIs and behave just as usual array buffers, except no direct access to bytes via typed arrays (maybe DataView is also possible).

[sebmarkbage]

Even without shared memory, the RN bridge could benefit from binary serialization and transferring ownership of memory. However, given the direction of the language, it might as well just be a shared reference.

[rclai]

This is also an issue for any kind of Bluetooth related functionality. Perhaps we should document current work-arounds for this?

[phoboslab]

FYI: I recently put a lot of time into a workaround for reading/writing Typed Arrays in native code and it seems to perform reasonably well. About 7ms/MB for reading, 20ms/MB for writing. The overhead of the read/write function call itself (regardless of array size) is ~0.2ms. The whole journey is documented here:
http://phoboslab.org/log/2015/11/the-absolute-worst-way-to-read-typed-array-data-with-javascriptcore

Final implementation: EJConvertTypedArray.h, EJConvertTypedArray.m

[vkurchatkin]

it looks like this API is finally being added to JSC

[rclai]

Wow really? You have a link for this?

[vkurchatkin]

@rclai https://bugs.webkit.org/show_bug.cgi?id=120112

[fungilation]

Looks like this is resolved and merged? #4483