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net: io.CopyN fails to copy from file to net.Conn on Windows [1.10 backport] #27419

FiloSottile opened this issue Aug 31, 2018 · 2 comments


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commented Aug 31, 2018

@rasky requested issue #25722 to be considered for backport to the next 1.10 minor release.

It's broken on Windows 10 and workarounds are difficult if the CopyN call happens deep into some networking library.


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commented Nov 1, 2018

Change mentions this issue: [release-branch.go1.10] internal/poll: advance file position in windows sendfile

gopherbot pushed a commit that referenced this issue Nov 1, 2018

[release-branch.go1.10] internal/poll: advance file position in windo…
…ws sendfile

Some versions of Windows (Windows 10 1803) do not set file
position after TransmitFile completes. So just use Seek
to set file position before returning from sendfile.

Updates #25722
Fixes #27419

Change-Id: I7a49be10304b5db19dda707b13ac93d338aeb190
Reviewed-by: Brad Fitzpatrick <>
Reviewed-by: Ian Lance Taylor <>
Reviewed-by: Yasuhiro MATSUMOTO <>
Run-TryBot: Brad Fitzpatrick <>
TryBot-Result: Gobot Gobot <>
(cherry picked from commit 8359b5e)
Run-TryBot: Ian Lance Taylor <>

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commented Nov 1, 2018

Closed by merging 13a2f53 to release-branch.go1.10.

@gopherbot gopherbot closed this Nov 1, 2018

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