Optimized request prefill error messages

Signed-off-by: learner0810 <zhongjun.li@daocloud.io>

Author: learner0810

pkg/sidecar/proxy/connector_nixlv2.go

@@ -130,10 +130,19 @@ func (s *Server) runNIXLProtocolV2(w http.ResponseWriter, r *http.Request, prefi
 	)
 
 	if isHTTPError(pw.statusCode) {
-		s.logger.Error(err, "request failed", "code", pw.statusCode)
+		s.logger.Error(err, "request failed", "code", pw.statusCode, "body", pw.buffer.String())
 		prefillSpan.SetStatus(codes.Error, "prefill request failed")
 		prefillSpan.End()
+		for key, values := range pw.Header() {
+			for _, v := range values {
+				w.Header().Add(key, v)
+			}
+		}
 		w.WriteHeader(pw.statusCode)
+		_, err := w.Write([]byte(pw.buffer.String()))
+		if err != nil {
+			s.logger.Error(err, "failed to send error response to client")
+		}
 		return
 	}
 	prefillSpan.End()