XTLS/Xray-core · info

failed to deliver response payload

Error message

failed to deliver response payload

What it means

Downlink copy from the fallback backend to the trojan client failed (buf.Copy serverReader→writer on the client conn) during fallback relaying. AtInfo severity, same best-effort rationale as [732].

Source

Thrown at proxy/trojan/server.go:537

				p2, _ := strconv.ParseUint(localPort, 10, 16)
				common.Must2(pro.Write([]byte{byte(p1 >> 8), byte(p1), byte(p2 >> 8), byte(p2)}))
			}
			if err := serverWriter.WriteMultiBuffer(buf.MultiBuffer{pro}); err != nil {
				return errors.New("failed to set PROXY protocol v", fb.Xver).Base(err).AtWarning()
			}
		}
		if err := buf.Copy(reader, serverWriter, buf.UpdateActivity(timer)); err != nil {
			return errors.New("failed to fallback request payload").Base(err).AtInfo()
		}
		return nil
	}

	writer := buf.NewWriter(connection)

	getResponse := func() error {
		defer timer.SetTimeout(sessionPolicy.Timeouts.UplinkOnly)
		if err := buf.Copy(serverReader, writer, buf.UpdateActivity(timer)); err != nil {
			return errors.New("failed to deliver response payload").Base(err).AtInfo()
		}
		return nil
	}

	if err := task.Run(ctx, task.OnSuccess(postRequest, task.Close(serverWriter)), task.OnSuccess(getResponse, task.Close(writer))); err != nil {
		common.Must(common.Interrupt(serverReader))
		common.Must(common.Interrupt(serverWriter))
		return errors.New("fallback ends").Base(err).AtInfo()
	}

	return nil
}

View on GitHub (pinned to 7d214f8b09)

Solutions

1. No action needed if fallback responses are being served in general
2. If responses never reach clients, verify TLS certificates on the fallback path match the SNI clients send
3. Correlate with the Base error to confirm it is a client-side write failure

if err := buf.Copy(serverReader, writer, buf.UpdateActivity(timer)); err != nil {
    // client vanished while the backend responded; end fallback quietly
    return errors.New("failed to deliver response payload").Base(err).AtInfo()
}

When it happens

Trigger: Client TLS connection resets while the backend is still responding, or the context is cancelled by the inactivity timer during the UplinkOnly window.

Common situations: Prober timeouts, client closing on large error pages, mobile network churn.

Related errors

• failed to fallback request payload
• Trojan fallbacks: "path" must be empty or start with "/"
• Trojan fallbacks: please fill in a valid value for every "de
• Trojan fallbacks: invalid PROXY protocol version, "xver" onl
• unexpected EOF

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/ed932c47cbd6c350. Report an issue: GitHub.