diff --git a/client/main.go b/client/main.go
index fb55b37..c026442 100644
--- a/client/main.go
+++ b/client/main.go
@@ -18,6 +18,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/urfave/cli"
 	kcp "github.com/xtaci/kcp-go"
+	"github.com/xtaci/kcptun/generic"
 	"github.com/xtaci/smux"
 
 	"path/filepath"
@@ -86,21 +87,11 @@ func handleClient(sess *smux.Session, p1 io.ReadWriteCloser, quiet bool) {
 	wg.Add(2)
 	// start tunnel & wait for tunnel termination
 	streamCopy := func(dst io.Writer, src io.ReadCloser) {
-		if wt, ok := src.(io.WriterTo); ok {
-			if _, err := wt.WriteTo(dst); err != nil {
-				logln(err)
-			}
-		} else if rt, ok := dst.(io.ReaderFrom); ok {
-			if _, err := rt.ReadFrom(src); err != nil {
-				logln(err)
-			}
-		} else {
-			buf := xmitBuf.Get().([]byte)
-			if _, err := io.CopyBuffer(dst, src, buf); err != nil {
-				logln(err)
-			}
-			xmitBuf.Put(buf)
+		buf := xmitBuf.Get().([]byte)
+		if _, err := generic.CopyBuffer(dst, src, buf); err != nil {
+			logln(err)
 		}
+		xmitBuf.Put(buf)
 		src.Close()
 		wg.Done()
 	}
diff --git a/generic/copy.go b/generic/copy.go
new file mode 100644
index 0000000..023556b
--- /dev/null
+++ b/generic/copy.go
@@ -0,0 +1,36 @@
+package generic
+
+import "io"
+
+// io.CopyBuffer has extra tests for interface like io.ReaderFrom and io.WriterTo
+// which is not efficient in memory management from tests
+func CopyBuffer(dst io.Writer, src io.Reader, buf []byte) (written int64, err error) {
+	if buf != nil && len(buf) == 0 {
+		panic("empty buffer in copyBuffer")
+	}
+
+	for {
+		nr, er := src.Read(buf)
+		if nr > 0 {
+			nw, ew := dst.Write(buf[0:nr])
+			if nw > 0 {
+				written += int64(nw)
+			}
+			if ew != nil {
+				err = ew
+				break
+			}
+			if nr != nw {
+				err = io.ErrShortWrite
+				break
+			}
+		}
+		if er != nil {
+			if er != io.EOF {
+				err = er
+			}
+			break
+		}
+	}
+	return written, err
+}
diff --git a/server/main.go b/server/main.go
index e55cd26..659927b 100644
--- a/server/main.go
+++ b/server/main.go
@@ -22,6 +22,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/urfave/cli"
 	kcp "github.com/xtaci/kcp-go"
+	"github.com/xtaci/kcptun/generic"
 	"github.com/xtaci/smux"
 )
 
@@ -113,21 +114,11 @@ func handleClient(p1 *smux.Stream, p2 io.ReadWriteCloser, quiet bool) {
 	wg.Add(2)
 	// start tunnel & wait for tunnel termination
 	streamCopy := func(dst io.Writer, src io.ReadCloser) {
-		if wt, ok := src.(io.WriterTo); ok {
-			if _, err := wt.WriteTo(dst); err != nil {
-				logln(err)
-			}
-		} else if rt, ok := dst.(io.ReaderFrom); ok {
-			if _, err := rt.ReadFrom(src); err != nil {
-				logln(err)
-			}
-		} else {
-			buf := xmitBuf.Get().([]byte)
-			if _, err := io.CopyBuffer(dst, src, buf); err != nil {
-				logln(err)
-			}
-			xmitBuf.Put(buf)
+		buf := xmitBuf.Get().([]byte)
+		if _, err := generic.CopyBuffer(dst, src, buf); err != nil {
+			logln(err)
 		}
+		xmitBuf.Put(buf)
 		src.Close()
 		wg.Done()
 	}