1 files changed, 238 insertions, 0 deletions
diff --git a/src/compress/lzw/writer_test.go b/src/compress/lzw/writer_test.go
new file mode 100644
index 0000000..edf683a
--- /dev/null
+++ b/src/compress/lzw/writer_test.go
@@ -0,0 +1,238 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package lzw
+
+import (
+	"bytes"
+	"fmt"
+	"internal/testenv"
+	"io"
+	"math"
+	"os"
+	"runtime"
+	"testing"
+)
+
+var filenames = []string{
+	"../testdata/gettysburg.txt",
+	"../testdata/e.txt",
+	"../testdata/pi.txt",
+}
+
+// testFile tests that compressing and then decompressing the given file with
+// the given options yields equivalent bytes to the original file.
+func testFile(t *testing.T, fn string, order Order, litWidth int) {
+	// Read the file, as golden output.
+	golden, err := os.Open(fn)
+	if err != nil {
+		t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err)
+		return
+	}
+	defer golden.Close()
+
+	// Read the file again, and push it through a pipe that compresses at the write end, and decompresses at the read end.
+	raw, err := os.Open(fn)
+	if err != nil {
+		t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err)
+		return
+	}
+
+	piper, pipew := io.Pipe()
+	defer piper.Close()
+	go func() {
+		defer raw.Close()
+		defer pipew.Close()
+		lzww := NewWriter(pipew, order, litWidth)
+		defer lzww.Close()
+		var b [4096]byte
+		for {
+			n, err0 := raw.Read(b[:])
+			if err0 != nil && err0 != io.EOF {
+				t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err0)
+				return
+			}
+			_, err1 := lzww.Write(b[:n])
+			if err1 != nil {
+				t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err1)
+				return
+			}
+			if err0 == io.EOF {
+				break
+			}
+		}
+	}()
+	lzwr := NewReader(piper, order, litWidth)
+	defer lzwr.Close()
+
+	// Compare the two.
+	b0, err0 := io.ReadAll(golden)
+	b1, err1 := io.ReadAll(lzwr)
+	if err0 != nil {
+		t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err0)
+		return
+	}
+	if err1 != nil {
+		t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err1)
+		return
+	}
+	if len(b1) != len(b0) {
+		t.Errorf("%s (order=%d litWidth=%d): length mismatch %d != %d", fn, order, litWidth, len(b1), len(b0))
+		return
+	}
+	for i := 0; i < len(b0); i++ {
+		if b1[i] != b0[i] {
+			t.Errorf("%s (order=%d litWidth=%d): mismatch at %d, 0x%02x != 0x%02x\n", fn, order, litWidth, i, b1[i], b0[i])
+			return
+		}
+	}
+}
+
+func TestWriter(t *testing.T) {
+	for _, filename := range filenames {
+		for _, order := range [...]Order{LSB, MSB} {
+			// The test data "2.71828 etcetera" is ASCII text requiring at least 6 bits.
+			for litWidth := 6; litWidth <= 8; litWidth++ {
+				if filename == "../testdata/gettysburg.txt" && litWidth == 6 {
+					continue
+				}
+				testFile(t, filename, order, litWidth)
+			}
+		}
+		if testing.Short() && testenv.Builder() == "" {
+			break
+		}
+	}
+}
+
+func TestWriterReset(t *testing.T) {
+	for _, order := range [...]Order{LSB, MSB} {
+		t.Run(fmt.Sprintf("Order %d", order), func(t *testing.T) {
+			for litWidth := 6; litWidth <= 8; litWidth++ {
+				t.Run(fmt.Sprintf("LitWidth %d", litWidth), func(t *testing.T) {
+					var data []byte
+					if litWidth == 6 {
+						data = []byte{1, 2, 3}
+					} else {
+						data = []byte(`lorem ipsum dolor sit amet`)
+					}
+					var buf bytes.Buffer
+					w := NewWriter(&buf, order, litWidth)
+					if _, err := w.Write(data); err != nil {
+						t.Errorf("write: %v: %v", string(data), err)
+					}
+
+					if err := w.Close(); err != nil {
+						t.Errorf("close: %v", err)
+					}
+
+					b1 := buf.Bytes()
+					buf.Reset()
+
+					w.(*Writer).Reset(&buf, order, litWidth)
+
+					if _, err := w.Write(data); err != nil {
+						t.Errorf("write: %v: %v", string(data), err)
+					}
+
+					if err := w.Close(); err != nil {
+						t.Errorf("close: %v", err)
+					}
+					b2 := buf.Bytes()
+
+					if !bytes.Equal(b1, b2) {
+						t.Errorf("bytes written were not same")
+					}
+				})
+			}
+		})
+	}
+}
+
+func TestWriterReturnValues(t *testing.T) {
+	w := NewWriter(io.Discard, LSB, 8)
+	n, err := w.Write([]byte("asdf"))
+	if n != 4 || err != nil {
+		t.Errorf("got %d, %v, want 4, nil", n, err)
+	}
+}
+
+func TestSmallLitWidth(t *testing.T) {
+	w := NewWriter(io.Discard, LSB, 2)
+	if _, err := w.Write([]byte{0x03}); err != nil {
+		t.Fatalf("write a byte < 1<<2: %v", err)
+	}
+	if _, err := w.Write([]byte{0x04}); err == nil {
+		t.Fatal("write a byte >= 1<<2: got nil error, want non-nil")
+	}
+}
+
+func TestStartsWithClearCode(t *testing.T) {
+	// A literal width of 7 bits means that the code width starts at 8 bits,
+	// which makes it easier to visually inspect the output (provided that the
+	// output is short so codes don't get longer). Each byte is a code:
+	//  - ASCII bytes are literal codes,
+	//  - 0x80 is the clear code,
+	//  - 0x81 is the end code.
+	//  - 0x82 and above are copy codes (unused in this test case).
+	for _, empty := range []bool{false, true} {
+		var buf bytes.Buffer
+		w := NewWriter(&buf, LSB, 7)
+		if !empty {
+			w.Write([]byte("Hi"))
+		}
+		w.Close()
+		got := buf.String()
+
+		want := "\x80\x81"
+		if !empty {
+			want = "\x80Hi\x81"
+		}
+
+		if got != want {
+			t.Errorf("empty=%t: got %q, want %q", empty, got, want)
+		}
+	}
+}
+
+func BenchmarkEncoder(b *testing.B) {
+	buf, err := os.ReadFile("../testdata/e.txt")
+	if err != nil {
+		b.Fatal(err)
+	}
+	if len(buf) == 0 {
+		b.Fatalf("test file has no data")
+	}
+
+	for e := 4; e <= 6; e++ {
+		n := int(math.Pow10(e))
+		buf0 := buf
+		buf1 := make([]byte, n)
+		for i := 0; i < n; i += len(buf0) {
+			if len(buf0) > n-i {
+				buf0 = buf0[:n-i]
+			}
+			copy(buf1[i:], buf0)
+		}
+		buf0 = nil
+		runtime.GC()
+		b.Run(fmt.Sprint("1e", e), func(b *testing.B) {
+			b.SetBytes(int64(n))
+			for i := 0; i < b.N; i++ {
+				w := NewWriter(io.Discard, LSB, 8)
+				w.Write(buf1)
+				w.Close()
+			}
+		})
+		b.Run(fmt.Sprint("1e-Reuse", e), func(b *testing.B) {
+			b.SetBytes(int64(n))
+			w := NewWriter(io.Discard, LSB, 8)
+			for i := 0; i < b.N; i++ {
+				w.Write(buf1)
+				w.Close()
+				w.(*Writer).Reset(io.Discard, LSB, 8)
+			}
+		})
+	}
+}