1 files changed, 69 insertions, 12 deletions

diff --git a/src/compress/flate/deflate_test.go b/src/compress/flate/deflate_test.go
index 49a0345fd1..6fc5abf4d5 100644
--- a/src/compress/flate/deflate_test.go
+++ b/src/compress/flate/deflate_test.go
@@ -11,6 +11,7 @@ import (
 	"internal/testenv"
 	"io"
 	"io/ioutil"
+	"math/rand"
 	"reflect"
 	"runtime/debug"
 	"sync"
@@ -156,7 +157,7 @@ func TestVeryLongSparseChunk(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping sparse chunk during short test")
 	}
-	w, err := NewWriter(ioutil.Discard, 1)
+	w, err := NewWriter(io.Discard, 1)
 	if err != nil {
 		t.Errorf("NewWriter: %v", err)
 		return
@@ -293,7 +294,7 @@ func testSync(t *testing.T, level int, input []byte, name string) {
 
 	// stream should work for ordinary reader too
 	r = NewReader(buf1)
-	out, err = ioutil.ReadAll(r)
+	out, err = io.ReadAll(r)
 	if err != nil {
 		t.Errorf("testSync: read: %s", err)
 		return
@@ -321,7 +322,7 @@ func testToFromWithLevelAndLimit(t *testing.T, level int, input []byte, name str
 		t.Logf("level: %d, size:%.2f%%, %d b\n", level, float64(buffer.Len()*100)/float64(limit), buffer.Len())
 	}
 	r := NewReader(&buffer)
-	out, err := ioutil.ReadAll(r)
+	out, err := io.ReadAll(r)
 	if err != nil {
 		t.Errorf("read: %s", err)
 		return
@@ -414,7 +415,7 @@ func TestReaderDict(t *testing.T) {
 	w.Close()
 
 	r := NewReaderDict(&b, []byte(dict))
-	data, err := ioutil.ReadAll(r)
+	data, err := io.ReadAll(r)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -455,7 +456,7 @@ func TestRegression2508(t *testing.T) {
 		t.Logf("test disabled with -short")
 		return
 	}
-	w, err := NewWriter(ioutil.Discard, 1)
+	w, err := NewWriter(io.Discard, 1)
 	if err != nil {
 		t.Fatalf("NewWriter: %v", err)
 	}
@@ -474,7 +475,7 @@ func TestWriterReset(t *testing.T) {
 		if testing.Short() && level > 1 {
 			break
 		}
-		w, err := NewWriter(ioutil.Discard, level)
+		w, err := NewWriter(io.Discard, level)
 		if err != nil {
 			t.Fatalf("NewWriter: %v", err)
 		}
@@ -486,9 +487,9 @@ func TestWriterReset(t *testing.T) {
 		for i := 0; i < n; i++ {
 			w.Write(buf)
 		}
-		w.Reset(ioutil.Discard)
+		w.Reset(io.Discard)
 
-		wref, err := NewWriter(ioutil.Discard, level)
+		wref, err := NewWriter(io.Discard, level)
 		if err != nil {
 			t.Fatalf("NewWriter: %v", err)
 		}
@@ -653,7 +654,7 @@ func TestBestSpeed(t *testing.T) {
 				}
 
 				r := NewReader(buf)
-				got, err := ioutil.ReadAll(r)
+				got, err := io.ReadAll(r)
 				if err != nil {
 					t.Errorf("i=%d, firstN=%d, flush=%t: ReadAll: %v", i, firstN, flush, err)
 					continue
@@ -880,7 +881,7 @@ func TestBestSpeedMaxMatchOffset(t *testing.T) {
 				}
 
 				r := NewReader(buf)
-				dst, err := ioutil.ReadAll(r)
+				dst, err := io.ReadAll(r)
 				r.Close()
 				if err != nil {
 					report("ReadAll: ", err)
@@ -896,6 +897,62 @@ func TestBestSpeedMaxMatchOffset(t *testing.T) {
 	}
 }
 
+func TestBestSpeedShiftOffsets(t *testing.T) {
+	// Test if shiftoffsets properly preserves matches and resets out-of-range matches
+	// seen in https://github.com/golang/go/issues/4142
+	enc := newDeflateFast()
+
+	// testData may not generate internal matches.
+	testData := make([]byte, 32)
+	rng := rand.New(rand.NewSource(0))
+	for i := range testData {
+		testData[i] = byte(rng.Uint32())
+	}
+
+	// Encode the testdata with clean state.
+	// Second part should pick up matches from the first block.
+	wantFirstTokens := len(enc.encode(nil, testData))
+	wantSecondTokens := len(enc.encode(nil, testData))
+
+	if wantFirstTokens <= wantSecondTokens {
+		t.Fatalf("test needs matches between inputs to be generated")
+	}
+	// Forward the current indicator to before wraparound.
+	enc.cur = bufferReset - int32(len(testData))
+
+	// Part 1 before wrap, should match clean state.
+	got := len(enc.encode(nil, testData))
+	if wantFirstTokens != got {
+		t.Errorf("got %d, want %d tokens", got, wantFirstTokens)
+	}
+
+	// Verify we are about to wrap.
+	if enc.cur != bufferReset {
+		t.Errorf("got %d, want e.cur to be at bufferReset (%d)", enc.cur, bufferReset)
+	}
+
+	// Part 2 should match clean state as well even if wrapped.
+	got = len(enc.encode(nil, testData))
+	if wantSecondTokens != got {
+		t.Errorf("got %d, want %d token", got, wantSecondTokens)
+	}
+
+	// Verify that we wrapped.
+	if enc.cur >= bufferReset {
+		t.Errorf("want e.cur to be < bufferReset (%d), got %d", bufferReset, enc.cur)
+	}
+
+	// Forward the current buffer, leaving the matches at the bottom.
+	enc.cur = bufferReset
+	enc.shiftOffsets()
+
+	// Ensure that no matches were picked up.
+	got = len(enc.encode(nil, testData))
+	if wantFirstTokens != got {
+		t.Errorf("got %d, want %d tokens", got, wantFirstTokens)
+	}
+}
+
 func TestMaxStackSize(t *testing.T) {
 	// This test must not run in parallel with other tests as debug.SetMaxStack
 	// affects all goroutines.
@@ -911,7 +968,7 @@ func TestMaxStackSize(t *testing.T) {
 		wg.Add(1)
 		go func(level int) {
 			defer wg.Done()
-			zw, err := NewWriter(ioutil.Discard, level)
+			zw, err := NewWriter(io.Discard, level)
 			if err != nil {
 				t.Errorf("level %d, NewWriter() = %v, want nil", level, err)
 			}
@@ -921,7 +978,7 @@ func TestMaxStackSize(t *testing.T) {
 			if err := zw.Close(); err != nil {
 				t.Errorf("level %d, Close() = %v, want nil", level, err)
 			}
-			zw.Reset(ioutil.Discard)
+			zw.Reset(io.Discard)
 		}(level)
 	}
 }