Added RLE compression. Closes #171

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()
+}