handle empty slices properly

go/cgzip/adler32.go

@@ -30,7 +30,9 @@ func NewAdler32() hash.Hash32 {
 
 // io.Writer interface
 func (a *adler32Hash) Write(p []byte) (n int, err error) {
-	a.adler = C.adler32(a.adler, (*C.Bytef)(unsafe.Pointer(&p[0])), (C.uInt)(len(p)))
+	if len(p) > 0 {
+		a.adler = C.adler32(a.adler, (*C.Bytef)(unsafe.Pointer(&p[0])), (C.uInt)(len(p)))
+	}
 	return len(p), nil
 }
 

go/cgzip/crc32.go

@@ -30,7 +30,9 @@ func NewCrc32() hash.Hash32 {
 
 // io.Writer interface
 func (a *crc32Hash) Write(p []byte) (n int, err error) {
-	a.crc = C.crc32(a.crc, (*C.Bytef)(unsafe.Pointer(&p[0])), (C.uInt)(len(p)))
+	if len(p) > 0 {
+		a.crc = C.crc32(a.crc, (*C.Bytef)(unsafe.Pointer(&p[0])), (C.uInt)(len(p)))
+	}
 	return len(p), nil
 }
 

go/cgzip/reader.go

@@ -57,6 +57,10 @@ func (z *reader) Read(p []byte) (int, error) {
 		return 0, z.err
 	}
 
+	if len(p) == 0 {
+		return 0, nil
+	}
+
 	// read and deflate until the output buffer is full
 	z.strm.next_out = (*C.Bytef)(unsafe.Pointer(&p[0]))
 	z.strm.avail_out = (C.uInt)(len(p))

go/cgzip/writer.go

@@ -95,7 +95,7 @@ func NewWriterLevelBuffer(w io.Writer, level, bufferSize int) (*Writer, error) {
 // this is the main function: it advances the write with either
 // new data or something else to do, like a flush
 func (z *Writer) write(p []byte, flush int) int {
-	if p == nil {
+	if len(p) == 0 {
 		z.strm.next_in = (*C.Bytef)(unsafe.Pointer(nil))
 		z.strm.avail_in = 0
 	} else {