go doc

pkg/bsdiff/bsdiff.go

@@ -35,8 +35,6 @@ import (
 	"github.com/gabstv/go-bsdiff/pkg/util"
 )
 
-// https://github.com/cnSchwarzer/bsdiff-win/blob/master/bsdiff-win/bsdiff.c
-
 // Bytes takes the old and new byte slices and outputs the diff
 func Bytes(oldbs, newbs []byte) ([]byte, error) {
 	return diffb(oldbs, newbs)
@@ -94,7 +92,7 @@ func diffb(oldbin, newbin []byte) ([]byte, error) {
 	var dblen, eblen int
 
 	// create the patch file
-	pf := new(BufWriter)
+	pf := new(util.BufWriter)
 
 	// Header is
 	//	0	8	 "BSDIFF40"

pkg/util/io.go

@@ -3,6 +3,7 @@ package util
 import (
 	"fmt"
 	"io"
+	"sync"
 )
 
 const (
@@ -45,3 +46,62 @@ func Min(a, b int) int {
 	}
 	return b
 }
+
+// BufWriter is byte slice buffer that implements io.WriteSeeker
+type BufWriter struct {
+	lock sync.Mutex
+	buf  []byte
+	pos  int
+}
+
+// Write the contents of p and return the bytes written
+func (m *BufWriter) Write(p []byte) (n int, err error) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	if m.buf == nil {
+		m.buf = make([]byte, 0)
+		m.pos = 0
+	}
+	minCap := m.pos + len(p)
+	if minCap > cap(m.buf) { // Make sure buf has enough capacity:
+		buf2 := make([]byte, len(m.buf), minCap+len(p)) // add some extra
+		copy(buf2, m.buf)
+		m.buf = buf2
+	}
+	if minCap > len(m.buf) {
+		m.buf = m.buf[:minCap]
+	}
+	copy(m.buf[m.pos:], p)
+	m.pos += len(p)
+	return len(p), nil
+}
+
+// Seek to a position on the byte slice
+func (m *BufWriter) Seek(offset int64, whence int) (int64, error) {
+	newPos, offs := 0, int(offset)
+	switch whence {
+	case io.SeekStart:
+		newPos = offs
+	case io.SeekCurrent:
+		newPos = m.pos + offs
+	case io.SeekEnd:
+		newPos = len(m.buf) + offs
+	}
+	if newPos < 0 {
+		return 0, fmt.Errorf("negative result pos")
+	}
+	m.pos = newPos
+	return int64(newPos), nil
+}
+
+// Len returns the length of the internal byte slice
+func (m *BufWriter) Len() int {
+	return len(m.buf)
+}
+
+// Bytes return a copy of the internal byte slice
+func (m *BufWriter) Bytes() []byte {
+	b2 := make([]byte, len(m.buf))
+	copy(b2, m.buf)
+	return b2
+}