internal/pkg: decompress zstd streams

This uses internal/zstd until compress/zstd becomes available.

Signed-off-by: Ophestra <cat@gensokyo.uk>

1 files changed, 72 insertions, 0 deletions

diff --git a/internal/zstd/window_test.go b/internal/zstd/window_test.go
new file mode 100644
index 00000000..afa2eefc
--- /dev/null
+++ b/internal/zstd/window_test.go
@@ -0,0 +1,72 @@
+// Copyright 2023 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 zstd
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+)
+
+func makeSequence(start, n int) (seq []byte) {
+	for i := 0; i < n; i++ {
+		seq = append(seq, byte(start+i))
+	}
+	return
+}
+
+func TestWindow(t *testing.T) {
+	for size := 0; size <= 3; size++ {
+		for i := 0; i <= 2*size; i++ {
+			a := makeSequence('a', i)
+			for j := 0; j <= 2*size; j++ {
+				b := makeSequence('a'+i, j)
+				for k := 0; k <= 2*size; k++ {
+					c := makeSequence('a'+i+j, k)
+
+					t.Run(fmt.Sprintf("%d-%d-%d-%d", size, i, j, k), func(t *testing.T) {
+						testWindow(t, size, a, b, c)
+					})
+				}
+			}
+		}
+	}
+}
+
+// testWindow tests window by saving three sequences of bytes to it.
+// Third sequence tests read offset that can become non-zero only after second save.
+func testWindow(t *testing.T, size int, a, b, c []byte) {
+	var w window
+	w.reset(size)
+
+	w.save(a)
+	w.save(b)
+	w.save(c)
+
+	var tail []byte
+	tail = append(tail, a...)
+	tail = append(tail, b...)
+	tail = append(tail, c...)
+
+	if len(tail) > size {
+		tail = tail[len(tail)-size:]
+	}
+
+	if w.len() != uint32(len(tail)) {
+		t.Errorf("wrong data length: got: %d, want: %d", w.len(), len(tail))
+	}
+
+	var from, to uint32
+	for from = 0; from <= uint32(len(tail)); from++ {
+		for to = from; to <= uint32(len(tail)); to++ {
+			got := w.appendTo(nil, from, to)
+			want := tail[from:to]
+
+			if !bytes.Equal(got, want) {
+				t.Errorf("wrong data at [%d:%d]: got %q, want %q", from, to, got, want)
+			}
+		}
+	}
+}