Work on creating tests for rsync api

tools/rsync/api_test.go

@@ -0,0 +1,77 @@
+// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package rsync
+
+import (
+	"bytes"
+	"fmt"
+	"kitty/tools/utils"
+	"kitty/tools/utils/random"
+	"testing"
+
+	"golang.org/x/exp/slices"
+)
+
+var _ = fmt.Print
+
+func TestRsyncRoundtrip(t *testing.T) {
+	src_data := make([]byte, 4*1024*1024)
+	random.Bytes(src_data)
+
+	random_patch := func(data []byte) (size int) {
+		if offset := random.Int(len(data)); offset < len(data) {
+			max_size := utils.Min(256, len(data)-offset)
+			if size = random.Int(max_size); size > 0 {
+				random.Bytes(data[offset : offset+size])
+			}
+		}
+		return
+	}
+
+	changed := slices.Clone(src_data)
+	for i := 0; i < 8; i++ {
+		random_patch(changed)
+	}
+
+	p := NewPatcher(int64(len(src_data)))
+	sigbuf := bytes.Buffer{}
+	if err := p.CreateSignature(bytes.NewReader(changed), func(p []byte) error { _, err := sigbuf.Write(p); return err }); err != nil {
+		t.Fatal(err)
+	}
+	d := NewDiffer()
+	if err := d.AddSignatureData(sigbuf.Bytes()); err != nil {
+		t.Fatal(err)
+	}
+	deltabuf := bytes.Buffer{}
+	if err := d.CreateDelta(bytes.NewReader(src_data), func(b []byte) error { _, err := deltabuf.Write(b); return err }); err != nil {
+		t.Fatal(err)
+	}
+	outputbuf := bytes.Buffer{}
+	p.StartDelta(&outputbuf, bytes.NewReader(src_data))
+	b := make([]byte, 30*1024)
+	for {
+		n, _ := deltabuf.Read(b)
+		if n <= 0 {
+			break
+		}
+		if err := p.UpdateDelta(b[:n]); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if err := p.FinishDelta(); err != nil {
+		t.Fatal(err)
+	}
+
+	output := outputbuf.Bytes()
+	if !bytes.Equal(src_data, output) {
+		first_diff := utils.Min(len(src_data), len(output))
+		for i := 0; i < first_diff; i++ {
+			if src_data[i] != output[i] {
+				first_diff = i
+				break
+			}
+		}
+		t.Fatalf("Patching failed: %d extra_bytes first different byte at: %d", len(outputbuf.Bytes())-len(src_data), first_diff)
+	}
+
+}