From: Olivier Mengué <olivier.mengue@gmail.com>
Date: Thu, 6 Mar 2025 18:44:22 +0000 (+0100)
Subject: archive/zip: preallocate fileList size for Reader.Open
X-Git-Tag: go1.25rc1~798
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=812a44ebd0a34ba2985f7f10c451fd210d5bab15;p=gostls13.git

archive/zip: preallocate fileList size for Reader.Open

When building the index of file entries for Reader.Open (when the Reader
is used as an io/fs.FS), reduce reallocations by pre-allocating the
count of entries based on the count of file entries.

Change-Id: I05048337cb5e752054b3e984a8a5ec5199c4589b
Reviewed-on: https://go-review.googlesource.com/c/go/+/655476
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
---

diff --git a/src/archive/zip/reader.go b/src/archive/zip/reader.go
index 2246d56558..963526db11 100644
--- a/src/archive/zip/reader.go
+++ b/src/archive/zip/reader.go
@@ -804,6 +804,9 @@ func toValidName(name string) string {
 
 func (r *Reader) initFileList() {
 	r.fileListOnce.Do(func() {
+		// Preallocate the minimum size of the index.
+		// We may also synthesize additional directory entries.
+		r.fileList = make([]fileListEntry, 0, len(r.File))
 		// files and knownDirs map from a file/directory name
 		// to an index into the r.fileList entry that we are
 		// building. They are used to mark duplicate entries.