repository cleanup

server/channelserver/compression/deltacomp/deltacomp.go

@@ -0,0 +1,105 @@
+package deltacomp
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+)
+
+func checkReadUint8(r *bytes.Reader) (uint8, error) {
+	b, err := r.ReadByte()
+	if err != nil {
+		return 0, err
+	}
+	return b, nil
+}
+
+func checkReadUint16(r *bytes.Reader) (uint16, error) {
+	data := make([]byte, 2)
+	n, err := r.Read(data)
+	if err != nil {
+		return 0, err
+	} else if n != len(data) {
+		return 0, io.EOF
+	}
+
+	return uint16(data[0])<<8 | uint16(data[1]), nil
+}
+
+func readCount(r *bytes.Reader) (int, error) {
+	var count int
+
+	count8, err := checkReadUint8(r)
+	if err != nil {
+		return 0, err
+	}
+	count = int(count8)
+
+	if count == 0 {
+		count16, err := checkReadUint16(r)
+		if err != nil {
+			return 0, err
+		}
+		count = int(count16)
+	}
+
+	return int(count), nil
+}
+
+// ApplyDataDiff applies a delta data diff patch onto given base data.
+func ApplyDataDiff(diff []byte, baseData []byte) []byte {
+	// Make a copy of the base data to return,
+	// (probably just make this modify the given slice in the future).
+	baseCopy := make([]byte, len(baseData))
+	copy(baseCopy, baseData)
+
+	patch := bytes.NewReader(diff)
+
+	// The very first matchCount is +1 more than it should be, so we start at -1.
+	dataOffset := -1
+	for {
+		// Read the amount of matching bytes.
+		matchCount, err := readCount(patch)
+		if err != nil {
+			// No more data
+			break
+		}
+
+		dataOffset += matchCount
+
+		// Read the amount of differing bytes.
+		differentCount, err := readCount(patch)
+		if err != nil {
+			// No more data
+			break
+		}
+		differentCount--
+
+		// Grow slice if it's required
+		if len(baseCopy) < dataOffset {
+			fmt.Printf("Slice smaller than data offset, growing slice...")
+			baseCopy = append(baseCopy, make([]byte, (dataOffset+differentCount)-len(baseData))...)
+		} else {
+			length := len(baseCopy[dataOffset:])
+			if length < differentCount {
+				length -= differentCount
+				baseCopy = append(baseCopy, make([]byte, length)...)
+			}
+		}
+
+		// Apply the patch bytes.
+		for i := 0; i < differentCount; i++ {
+			b, err := checkReadUint8(patch)
+			if err != nil {
+				panic("Invalid or misunderstood patch format!")
+			}
+
+			baseCopy[dataOffset+i] = b
+		}
+
+		dataOffset += differentCount - 1
+
+	}
+
+	return baseCopy
+}