Reduce the number of calls needed to (*MuxConn).Read

Also affects (*buffer).Read.

buffer.go

@@ -7,19 +7,27 @@ type buffer struct {
 	data []byte
 }
 
-func (b *buffer) Read(p []byte) (n int, err error) {
-	n = len(b.data) - b.read
-	if n == 0 {
-		return 0, io.EOF
-	}
-
-	if len(p) < n {
-		n = len(p)
-	}
-
-	copy(p[:n], b.data[b.read:b.read+n])
+// From the io.Reader documentation:
+//
+// When Read encounters an error or end-of-file condition after
+// successfully reading n > 0 bytes, it returns the number of
+// bytes read.  It may return the (non-nil) error from the same call
+// or return the error (and n == 0) from a subsequent call.
+// An instance of this general case is that a Reader returning
+// a non-zero number of bytes at the end of the input stream may
+// return either err == EOF or err == nil.  The next Read should
+// return 0, EOF.
+//
+// This function implements the latter behaviour, returning the
+// (non-nil) error from the same call.
+func (b *buffer) Read(p []byte) (int, error) {
+	var err error
+	n := copy(p, b.data[b.read:])
 	b.read += n
-	return
+	if b.read == len(b.data) {
+		err = io.EOF
+	}
+	return n, err
 }
 
 func (b *buffer) Len() int {