From 20944cf0665a5aec6abab802875a9700592b5391 Mon Sep 17 00:00:00 2001
From: Alexander Yastrebov <yastrebov.alex@gmail.com>
Date: Thu, 28 Sep 2023 22:26:57 +0000
Subject: [PATCH] internal/zstd: reset reader buffer

Reset r.buffer on Reset to avoid subsequent Read calls
observing previously decoded data.

For #62513

Change-Id: Icb65e76b5c5c0af32b36ec3a5999dca86407cbc8
GitHub-Last-Rev: 99c0a6fa72ad67cba5d29593fd3b28d14ddce4a4
GitHub-Pull-Request: golang/go#63288
Reviewed-on: https://go-review.googlesource.com/c/go/+/531735
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---
 src/internal/zstd/zstd.go      |  2 +-
 src/internal/zstd/zstd_test.go | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/internal/zstd/zstd.go b/src/internal/zstd/zstd.go
index 72d733f6dd..9cf62a6bac 100644
--- a/src/internal/zstd/zstd.go
+++ b/src/internal/zstd/zstd.go
@@ -104,7 +104,7 @@ func (r *Reader) Reset(input io.Reader) {
 	r.frameSizeUnknown = false
 	r.remainingFrameSize = 0
 	r.blockOffset = 0
-	// buffer
+	r.buffer = r.buffer[:0]
 	r.off = 0
 	// repeatedOffset1
 	// repeatedOffset2
diff --git a/src/internal/zstd/zstd_test.go b/src/internal/zstd/zstd_test.go
index 8c7f9403c1..70141b02d0 100644
--- a/src/internal/zstd/zstd_test.go
+++ b/src/internal/zstd/zstd_test.go
@@ -127,6 +127,26 @@ func TestSamples(t *testing.T) {
 	}
 }
 
+func TestReset(t *testing.T) {
+	input := strings.NewReader("")
+	r := NewReader(input)
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			input.Reset(test.compressed)
+			r.Reset(input)
+			got, err := io.ReadAll(r)
+			if err != nil {
+				t.Fatal(err)
+			}
+			gotstr := string(got)
+			if gotstr != test.uncompressed {
+				t.Errorf("got %q want %q", gotstr, test.uncompressed)
+			}
+		})
+	}
+}
+
 var (
 	bigDataOnce  sync.Once
 	bigDataBytes []byte