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syscall/js: no method to convert TypedArrays into slices #30210

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superp00t opened this issue Feb 13, 2019 · 4 comments
Closed

syscall/js: no method to convert TypedArrays into slices #30210

superp00t opened this issue Feb 13, 2019 · 4 comments
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arch-wasm WebAssembly issues FeatureRequest FrozenDueToAge NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made.

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@superp00t
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You can convert a Go slice into a TypedArray by using js.TypedArrayOf(...), but there is apparently no way of doing the reverse operation.

You can write a function to Index() every byte value in an ArrayBuffer and put them in a byte slice, but this is cumbersome and incurs unacceptable overhead. There should be a function to directly copy the bytes into the Go heap, such as what js.Value.String() does.
@katiehockman katiehockman changed the title syscall/js: No method to convert TypedArrays into Go slices syscall/js: no method to convert TypedArrays into Go slices Feb 14, 2019
@katiehockman katiehockman changed the title syscall/js: no method to convert TypedArrays into Go slices syscall/js: no method to convert TypedArrays into slices Feb 14, 2019
@katiehockman katiehockman added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Feb 14, 2019
@katiehockman
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/cc @neelance

@neelance
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WebAssembly is only able to access typed arrays which are backed by WebAssembly's memory. This does not hold for all typed arrays, so a mapping with direct access to the typed array is not possible. The best solution is to allocate a correctly sized byte slice in Go, pass it to JS with TypedArrayOf and then use https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/set to quickly copy all bytes.

@superp00t
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@neelance Thanks a lot, doing that solved my problem.

@bradfitz bradfitz added FeatureRequest arch-wasm WebAssembly issues labels Feb 14, 2019
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I added metadata to this CL before I read the final comment which makes it sounds like this bug is resolved. So, closing. Correct me if that's wrong.

@golang golang locked and limited conversation to collaborators Feb 14, 2020
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arch-wasm WebAssembly issues FeatureRequest FrozenDueToAge NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made.
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@bradfitz @neelance @gopherbot @superp00t @katiehockman