fix: return a grpc error when discard failed

Signed-off-by: ningmingxiao <ning.mingxiao@zte.com.cn>

Author: ningmingxiao

channel.go

@@ -19,6 +19,7 @@ package ttrpc
 import (
 	"bufio"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -124,11 +125,11 @@ func (ch *channel) recv() (messageHeader, []byte, error) {
 	}
 
 	if mh.Length > uint32(messageLengthMax) {
+		errRecv := status.Errorf(codes.ResourceExhausted, "message length %v exceed maximum message size of %v", mh.Length, messageLengthMax)
 		if _, err := ch.br.Discard(int(mh.Length)); err != nil {
-			return mh, nil, fmt.Errorf("failed to discard after receiving oversized message: %w", err)
+			errors.Join(errRecv, fmt.Errorf("failed to discard after receiving oversized message: %w", err))
 		}
-
-		return mh, nil, status.Errorf(codes.ResourceExhausted, "message length %v exceed maximum message size of %v", mh.Length, messageLengthMax)
+		return mh, nil, errRecv
 	}
 
 	var p []byte