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Add StreamExt::copy_into #1661

yoshuawuyts opened this issue Jun 6, 2019 · 0 comments


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commented Jun 6, 2019

Problem definition

Currently in order to move data from an AsyncRead into an AsyncWrite you can use the copy_into method.

However when wanting to move data from a Stream<Item = Vec<u8>> into an AsyncWrite, we have to perform the slightly awkward dance of:

This is not only hard to remember, but has a double buffering problem (see #1659 for a proposal to address this).


It'd be nice if copy_into would work for byte streams too:


This could be implemented along the lines of:

impl Stream<Item = AsRef<[u8]>> {
    pub fn copy_into(&mut self, writer: impl AsyncWrite) -> /* ret */ {
        self.for_each(move |buf| writer.write(buf))

impl Stream<Item = io::Result<AsRef<[u8]>>> {
    pub fn copy_into(&mut self, writer: impl AsyncWrite) -> /* ret */ {
        self.try_for_each(move |buf| writer.write(buf))

Other Considerations

So far I've only encountered example uses for this in the wild moving data from Stream -> AsyncWrite. It might be possible to add similar conversions for other traits too, but I think it would be best to keep the conversation about Stream<[u8]> -> AsyncWrite first, to limit the scope of this proposal.

Related Issues

@yoshuawuyts yoshuawuyts referenced this issue Jul 8, 2019


Stream::copy_into #1723

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