[Workers] Document streams_byob_reader_detaches_buffer compatibility flag #2644
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…flag This compatibility flag is new as of this week. Note that the text references a relatively new, non-standard method that we added to ReadableStream: `readAtLeast()`. Unfortunately, this method is not yet documented.
kentonv
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Nov 22, 2021
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| Originally, the Workers runtime did not detach the `ArrayBuffer`s from user-provided TypedArrays when using the [BYOB reader's `read()` method](/runtime-apis/streams/readablestreambyobreader#methods), as required by the Streams spec, meaning it was possible to inadvertently reuse the same buffer for multiple `read()` calls. This change brings us in line with the spec. | ||
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| User code should never try to reuse an `ArrayBuffer` that has been passed into a [BYOB reader's `read()` method](/runtime-apis/streams/readablestreambyobreader#methods). The more recently added extension method `readAtLeast()` will always detach the `ArrayBuffer` and is unaffected by this feature flag setting. |
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I think you can reuse the buffer, just not under the same reference? That is, when read() returns, it gives you a new reference to the buffer, which you can then use in the next call. This seems like the whole point of BYOB, to avoid allocation overhead, so we should probably be a bit clearer here.
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I added a little example.
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Sorry for failing to see this earlier, I have this repo muted because it was sending me too many notifications that weren't relevant to me... but that means I also missed a code review I was actually tagged on. :( |
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kentonv
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Nov 29, 2021
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LGTM but I guess my approval is not good enough as I'm not an owner. |
jasnell
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Nov 29, 2021
deadlypants1973
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This compatibility flag is new as of this week.
Note that the text references a relatively new, non-standard method that we added to ReadableStream:
readAtLeast(). Unfortunately, this method is not yet documented./cc @jasnell