bug: fix memory corruption for Conn.Next (#649)

Fixes #648 

---------

Co-authored-by: zhongweikang <[email protected]>

Author: zhongweikang

connection_unix.go

@@ -325,11 +325,11 @@ func (c *conn) Next(n int) (buf []byte, err error) {
 	}
 	head, tail := c.inboundBuffer.Peek(n)
 	defer c.inboundBuffer.Discard(n) //nolint:errcheck
-	if len(head) >= n {
-		return head[:n], err
-	}
 	c.loop.cache.Reset()
 	c.loop.cache.Write(head)
+	if len(head) >= n {
+		return c.loop.cache.Bytes(), err
+	}
 	c.loop.cache.Write(tail)
 	if inBufferLen >= n {
 		return c.loop.cache.Bytes(), err

connection_windows.go

@@ -164,11 +164,11 @@ func (c *conn) Next(n int) (buf []byte, err error) {
 	}
 	head, tail := c.inboundBuffer.Peek(n)
 	defer c.inboundBuffer.Discard(n) //nolint:errcheck
-	if len(head) >= n {
-		return head[:n], err
-	}
 	c.loop.cache.Reset()
 	c.loop.cache.Write(head)
+	if len(head) >= n {
+		return c.loop.cache.Bytes(), err
+	}
 	c.loop.cache.Write(tail)
 	if inBufferLen >= n {
 		return c.loop.cache.Bytes(), err