Never return -1 when a Read*() or Write*() call has an error (#8)

Return 0 or the number of bytes that were read/written up until the error occurred.

Fixes #6

Author: arashpayan

client.go

@@ -1102,7 +1102,7 @@ func (f *File) Read(b []byte) (n int, err error) {
 
 	off, err := f.seek(0, io.SeekCurrent)
 	if err != nil {
-		return -1, &os.PathError{Op: "read", Path: f.name, Err: err}
+		return 0, &os.PathError{Op: "read", Path: f.name, Err: err}
 	}
 
 	n, err = f.readAt(b, off)
@@ -1124,7 +1124,7 @@ func (f *File) Read(b []byte) (n int, err error) {
 // ReadAt implements io.ReaderAt.
 func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
 	if off < 0 {
-		return -1, os.ErrInvalid
+		return 0, os.ErrInvalid
 	}
 
 	n, err = f.readAt(b, off)
@@ -1181,7 +1181,7 @@ func (f *File) maxTransactSize() int {
 
 func (f *File) readAt(b []byte, off int64) (n int, err error) {
 	if off < 0 {
-		return -1, os.ErrInvalid
+		return 0, os.ErrInvalid
 	}
 
 	maxReadSize := f.maxReadSize()
@@ -1599,7 +1599,7 @@ func (f *File) Write(b []byte) (n int, err error) {
 
 	off, err := f.seek(0, io.SeekCurrent)
 	if err != nil {
-		return -1, &os.PathError{Op: "write", Path: f.name, Err: err}
+		return 0, &os.PathError{Op: "write", Path: f.name, Err: err}
 	}
 
 	n, err = f.writeAt(b, off)
@@ -1626,7 +1626,7 @@ func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
 
 func (f *File) writeAt(b []byte, off int64) (n int, err error) {
 	if off < 0 {
-		return -1, os.ErrInvalid
+		return 0, os.ErrInvalid
 	}
 
 	if len(b) == 0 {
@@ -1642,14 +1642,14 @@ func (f *File) writeAt(b []byte, off int64) (n int, err error) {
 		case len(b)-n <= maxWriteSize:
 			m, err := f.writeAtChunk(b[n:], int64(n)+off)
 			if err != nil {
-				return -1, err
+				return 0, err
 			}
 
 			n += m
 		default:
 			m, err := f.writeAtChunk(b[n:n+maxWriteSize], int64(n)+off)
 			if err != nil {
-				return -1, err
+				return 0, err
 			}
 
 			n += m

transport.go

@@ -30,7 +30,7 @@ func direct(tcpConn net.Conn) transport {
 
 func (t *directTCP) Write(p []byte) (n int, err error) {
 	if len(p) > maxDirectTCPSize {
-		return -1, errors.New("max transport size exceeds")
+		return 0, errors.New("max transport size exceeds")
 	}
 
 	bs := t.sb[:]
@@ -39,12 +39,12 @@ func (t *directTCP) Write(p []byte) (n int, err error) {
 
 	_, err = t.conn.Write(bs)
 	if err != nil {
-		return -1, err
+		return 0, err
 	}
 
 	n, err = t.conn.Write(p)
 	if err != nil {
-		return -1, err
+		return 0, err
 	}
 
 	return n + 4, nil
@@ -55,11 +55,11 @@ func (t *directTCP) ReadSize() (size int, err error) {
 
 	_, err = io.ReadFull(t.conn, bs)
 	if err != nil {
-		return -1, err
+		return 0, err
 	}
 
 	if bs[0] != 0 {
-		return -1, errors.New("invalid transport format")
+		return 0, errors.New("invalid transport format")
 	}
 
 	return int(be.Uint32(bs)), nil
@@ -68,7 +68,7 @@ func (t *directTCP) ReadSize() (size int, err error) {
 func (t *directTCP) Read(p []byte) (n int, err error) {
 	n, err = io.ReadFull(t.conn, p)
 	if err != nil {
-		return -1, err
+		return 0, err
 	}
 
 	return n, err