archive/zip: support zero-copy writing

[hanwen-flow]

Proposal Details

The fileWriter returned by CreateRaw does not do any
checksumming. Hence, we can bypass userspace for the copying if the
source is another file.

We don't have to add new methods/functions, but simply add ReadFrom to the io.Writer returned by CreateRaw.

Sample implementation in https://go-review.googlesource.com/c/go/+/665596

[hanwen-flow]

The other direction (reading a zip file with zero copy) is enabled by #73399, but can also easily be coded outside of the zip package by seeking to zip.File.DataOffset() and then using a io.LimitedReader.

[gabyhelp]

Related Issues

• archive/zip: add File.OpenRaw, Writer.CreateRaw, Writer.Copy #34974 (closed)
• archive/zip: make checksumReader implement io.WriterTo #56742 (closed)
• proposal: archive/tar: support zero-copy reading/writing #70807

Related Code Changes

• zip: support zero-copy for CreateRaw

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[gopherbot]

Change https://go.dev/cl/665596 mentions this issue: archive/zip: support zero-copy for CreateRaw

[seankhliao]

With no api change, i don't think this needs to be a proposal