From 9f8bcf3abca8c6c32efc384f6c6eda1677b769c5 Mon Sep 17 00:00:00 2001
From: obscuren <geffobscura@gmail.com>
Date: Sun, 2 Nov 2014 23:33:06 +0100
Subject: [PATCH] Added RLE compression. Closes #171

---
 compression/rle/read_write.go      | 82 ++++++++++++++++++++++++++
 compression/rle/read_write_test.go | 93 ++++++++++++++++++++++++++++++
 2 files changed, 175 insertions(+)
 create mode 100644 compression/rle/read_write.go
 create mode 100644 compression/rle/read_write_test.go

diff --git a/compression/rle/read_write.go b/compression/rle/read_write.go
new file mode 100644
index 0000000000..e6f78e3724
--- /dev/null
+++ b/compression/rle/read_write.go
@@ -0,0 +1,82 @@
+package rle
+
+import (
+	"bytes"
+	"errors"
+
+	"github.com/ethereum/go-ethereum/crypto"
+)
+
+const (
+	token             byte = 0xfe
+	emptyShaToken          = 0xfd
+	emptyListShaToken      = 0xfe
+	tokenToken             = 0xff
+)
+
+var empty = crypto.Sha3([]byte(""))
+var emptyList = crypto.Sha3([]byte{0x80})
+
+func Decompress(dat []byte) ([]byte, error) {
+	buf := new(bytes.Buffer)
+
+	for i := 0; i < len(dat); i++ {
+		if dat[i] == token {
+			if i+1 < len(dat) {
+				switch dat[i+1] {
+				case emptyShaToken:
+					buf.Write(empty)
+				case emptyListShaToken:
+					buf.Write(emptyList)
+				case tokenToken:
+					buf.WriteByte(token)
+				default:
+					buf.Write(make([]byte, int(dat[i+1]-2)))
+				}
+				i++
+			} else {
+				return nil, errors.New("error reading bytes. token encountered without proceeding bytes")
+			}
+		}
+	}
+
+	return buf.Bytes(), nil
+}
+
+func Compress(dat []byte) []byte {
+	buf := new(bytes.Buffer)
+
+	for i := 0; i < len(dat); i++ {
+		if dat[i] == token {
+			buf.Write([]byte{token, tokenToken})
+		} else if i+1 < len(dat) {
+			if dat[i] == 0x0 && dat[i+1] == 0x0 {
+				j := 0
+				for j <= 254 && i+j < len(dat) {
+					if dat[i+j] != 0 {
+						break
+					}
+					j++
+				}
+				buf.Write([]byte{token, byte(j + 2)})
+				i += (j - 1)
+			} else if len(dat[i:]) >= 32 {
+				if dat[i] == empty[0] && bytes.Compare(dat[i:i+32], empty) == 0 {
+					buf.Write([]byte{token, emptyShaToken})
+					i += 31
+				} else if dat[i] == emptyList[0] && bytes.Compare(dat[i:i+32], emptyList) == 0 {
+					buf.Write([]byte{token, emptyListShaToken})
+					i += 31
+				} else {
+					buf.WriteByte(dat[i])
+				}
+			} else {
+				buf.WriteByte(dat[i])
+			}
+		} else {
+			buf.WriteByte(dat[i])
+		}
+	}
+
+	return buf.Bytes()
+}
diff --git a/compression/rle/read_write_test.go b/compression/rle/read_write_test.go
new file mode 100644
index 0000000000..944822a47e
--- /dev/null
+++ b/compression/rle/read_write_test.go
@@ -0,0 +1,93 @@
+package rle
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/crypto"
+)
+
+func TestDecompressSimple(t *testing.T) {
+	res, err := Decompress([]byte{token, 0xfd})
+	if err != nil {
+		t.Error(err)
+	}
+	if bytes.Compare(res, crypto.Sha3([]byte(""))) != 0 {
+		t.Error("empty sha3", res)
+	}
+
+	res, err = Decompress([]byte{token, 0xfe})
+	if err != nil {
+		t.Error(err)
+	}
+	if bytes.Compare(res, crypto.Sha3([]byte{0x80})) != 0 {
+		t.Error("0x80 sha3", res)
+	}
+
+	res, err = Decompress([]byte{token, 0xff})
+	if err != nil {
+		t.Error(err)
+	}
+	if bytes.Compare(res, []byte{token}) != 0 {
+		t.Error("token", res)
+	}
+
+	res, err = Decompress([]byte{token, 12})
+	if err != nil {
+		t.Error(err)
+	}
+	if bytes.Compare(res, make([]byte, 10)) != 0 {
+		t.Error("10 * zero", res)
+	}
+}
+
+func TestDecompressMulti(t *testing.T) {
+	res, err := Decompress([]byte{token, 0xfd, token, 0xfe, token, 12})
+	if err != nil {
+		t.Error(err)
+	}
+
+	var exp []byte
+	exp = append(exp, crypto.Sha3([]byte(""))...)
+	exp = append(exp, crypto.Sha3([]byte{0x80})...)
+	exp = append(exp, make([]byte, 10)...)
+
+	if bytes.Compare(res, res) != 0 {
+		t.Error("Expected", exp, "result", res)
+	}
+}
+
+func TestCompressSimple(t *testing.T) {
+	res := Compress([]byte{0, 0, 0, 0, 0})
+	if bytes.Compare(res, []byte{token, 7}) != 0 {
+		t.Error("5 * zero", res)
+	}
+
+	res = Compress(crypto.Sha3([]byte("")))
+	if bytes.Compare(res, []byte{token, emptyShaToken}) != 0 {
+		t.Error("empty sha", res)
+	}
+
+	res = Compress(crypto.Sha3([]byte{0x80}))
+	if bytes.Compare(res, []byte{token, emptyListShaToken}) != 0 {
+		t.Error("empty list sha", res)
+	}
+
+	res = Compress([]byte{token})
+	if bytes.Compare(res, []byte{token, tokenToken}) != 0 {
+		t.Error("token", res)
+	}
+}
+
+func TestCompressMulti(t *testing.T) {
+	in := []byte{0, 0, 0, 0, 0}
+	in = append(in, crypto.Sha3([]byte(""))...)
+	in = append(in, crypto.Sha3([]byte{0x80})...)
+	in = append(in, token)
+	res := Compress(in)
+
+	exp := []byte{token, 7, token, emptyShaToken, token, emptyListShaToken, token, tokenToken}
+	if bytes.Compare(res, exp) != 0 {
+		t.Error("expected", exp, "got", res)
+	}
+}