From dbc90ba7a5f24db198cc3eab1c38aad665e41d06 Mon Sep 17 00:00:00 2001
From: Alexander Yastrebov <yastrebov.alex@gmail.com>
Date: Sat, 9 Sep 2023 01:58:07 +0200
Subject: [PATCH] internal/zstd: fix window resizing

Incorrect window resizing led to checksum error and invalid result.
To demonstrate the problem bigData must be a bit bigger, 3x is enough.

This change fixes window resizing, increases bigData size and
decouples TestLargeXXHash from bigData because it uses hardcoded hash
value.
---
 src/internal/zstd/xxhash_test.go | 6 +++++-
 src/internal/zstd/zstd.go        | 1 +
 src/internal/zstd/zstd_test.go   | 5 ++++-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/internal/zstd/xxhash_test.go b/src/internal/zstd/xxhash_test.go
index 646cee888a..032739fbc0 100644
--- a/src/internal/zstd/xxhash_test.go
+++ b/src/internal/zstd/xxhash_test.go
@@ -42,7 +42,11 @@ func TestLargeXXHash(t *testing.T) {
 		t.Skip("skipping expensive test in short mode")
 	}
 
-	data := bigData(t)
+	data, err := os.ReadFile("../../testdata/Isaac.Newton-Opticks.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	var xh xxhash64
 	xh.reset()
 	i := 0
diff --git a/src/internal/zstd/zstd.go b/src/internal/zstd/zstd.go
index a8607893cd..25a731c164 100644
--- a/src/internal/zstd/zstd.go
+++ b/src/internal/zstd/zstd.go
@@ -466,6 +466,7 @@ func (r *Reader) saveWindow(buf []byte) {
 	if keep < len(r.window) {
 		remove := len(r.window) - keep
 		copy(r.window[:], r.window[remove:])
+		r.window = r.window[:keep]
 	}
 
 	r.window = append(r.window, buf...)
diff --git a/src/internal/zstd/zstd_test.go b/src/internal/zstd/zstd_test.go
index bc75e0fb03..33f3def878 100644
--- a/src/internal/zstd/zstd_test.go
+++ b/src/internal/zstd/zstd_test.go
@@ -115,10 +115,13 @@ var (
 	bigDataErr   error
 )
 
-// bigData returns the contents of our large test file.
+// bigData returns the contents of our large test file repeated multiple times.
 func bigData(t testing.TB) []byte {
 	bigDataOnce.Do(func() {
 		bigDataBytes, bigDataErr = os.ReadFile("../../testdata/Isaac.Newton-Opticks.txt")
+		if bigDataErr == nil {
+			bigDataBytes = bytes.Repeat(bigDataBytes, 3)
+		}
 	})
 	if bigDataErr != nil {
 		t.Fatal(bigDataErr)