What causes "x_tunnel create conn fail" in XX-net/XX-Net?

Reduce concurrent connections through x-tunnel / raise its connection limit

x_tunnel create conn fail

Error message

x_tunnel create conn fail

What it means

create_conn returned a falsy conn_id (0/None), meaning x-tunnel could not allocate a connection. XTunnelNotRunning is raised so routing falls back.

Source

Thrown at code/default/smart_router/local/smart_route.py:252

    if left_buf:
        ssl_sock.send(left_buf)
    sw = SocketWrap(ssl_sock, remote_sock.ip, port, host)
    sock.recved_times = 3
    g.pipe_socks.add_socks(sock, sw)


def do_socks(sock, host, port, client_address, left_buf=b""):
    if not g.x_tunnel:
        raise XTunnelNotRunning()

    try:
        conn_id = g.x_tunnel.proxy_session.create_conn(sock, host, port, True)
    except Exception as e:
        xlog.warn("do_sock to %s:%d, x_tunnel fail:%r", host, port, e)
        raise XTunnelNotRunning()

    if not conn_id:
        xlog.warn("x_tunnel create conn fail")
        raise XTunnelNotRunning()

    # xlog.debug("do_socks %r connect to %s:%d conn_id:%d", client_address, host, port, conn_id)
    if left_buf:
        g.x_tunnel.global_var.session.conn_list[conn_id].transfer_received_data(left_buf)
    g.x_tunnel.global_var.session.conn_list[conn_id].start(block=True)


def do_unwrap_socks(sock, host, port, client_address, req, left_buf=b""):
    if not g.x_tunnel:
        return

    try:
        remote_sock = socks.create_connection(
            (host, port),
            proxy_type="socks5h", proxy_addr="127.0.0.1", proxy_port=g.x_tunnel_socks_port, timeout=15
        )
    except Exception as e:

View on GitHub (pinned to cfa5bc17b6)

Solutions

Reduce concurrent connections through x-tunnel / raise its connection limit
Re-establish the x-tunnel session (re-login/restart)
Inspect x-tunnel logs for why conn allocation failed
Fall back to direct or other proxy rules (automatic)

Defensive patterns

Strategy: fallback

Validate before calling

if active_conns() >= MAX_CONNS: use_next_rule()

Try / catch

Treat falsy conn_id as transport failure; fall back to next rule.

Prevention

Bound concurrent x-tunnel connections
Re-login x-tunnel on stale sessions

When it happens

Trigger: x-tunnel session accepts the call but fails to allocate a conn_id: session in a bad state, connection table exhausted, or server rejected the creation.

Common situations: Too many concurrent x-tunnel connections, half-dead session after network change, server-side resource limits.

Related errors

AI-assisted analysis of XX-net/XX-Net@cfa5bc17b6 (2026-08-27). Data as JSON: /api/errors/71d50c6008a49cca. Report an issue: GitHub.