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archive/zip: reduce memory held by Writer.Copy

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Make a copy of the argument File's FileHeader, and pass a pointer
to the copy to CreateRaw.

Passing the pointer directly causes the entire `File` to be referenced
by the receiver. The `File` includes a reference to the `ReaderAt`
underlying the `Reader`, so all its memory, which may be the entire
contents of the archive, is prevented from being garbage-collected.

Also, explain the issue in the doc comment for CreateRaw. We
cannot change its behavior because someone may depend on the
preserving the identity of its argument pointer.

For #65499.

Change-Id: Ieb4963a0ea30539d597547d3511accbd8c6b5c5a
Reviewed-on: https://go-review.googlesource.com/c/go/+/560238
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
This commit is contained in:
Jonathan Amsterdam 2024-02-03 11:48:50 -05:00
parent 6076edc55c
commit 6f44cc88f5
1 changed files with 8 additions and 1 deletions
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9
src/archive/zip/writer.go
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@ -433,6 +433,10 @@ func writeHeader(w io.Writer, h *header) error {
// [Writer.CreateHeader], [Writer.CreateRaw], or [Writer.Close].
//
// In contrast to [Writer.CreateHeader], the bytes passed to Writer are not compressed.
//
// CreateRaw's argument is stored in w. If the argument is a pointer to the embedded
// [FileHeader] in a [File] obtained from a [Reader] created from in-memory data,
// then w will refer to all of that memory.
func (w *Writer) CreateRaw(fh *FileHeader) (io.Writer, error) {
if err := w.prepare(fh); err != nil {
return nil, err
@ -471,7 +475,10 @@ func (w *Writer) Copy(f *File) error {
if err != nil {
return err
}
fw, err := w.CreateRaw(&f.FileHeader)
// Copy the FileHeader so w doesn't store a pointer to the data
// of f's entire archive. See #65499.
fh := f.FileHeader
fw, err := w.CreateRaw(&fh)
if err != nil {
return err
}