shadowsocks/shadowsocks-windows · error · NotSupportedException

Unknown forward proxy.

Error message

Unknown forward proxy.

What it means

Thrown as NotSupportedException when config.useProxy is true but config.proxyType does not match PROXY_SOCKS5 or PROXY_HTTP. Only those two forward-proxy types are implemented; any other value falls through the switch's default. It fires during remote connection setup, before a proxy endpoint is resolved.

Source

Thrown at shadowsocks-csharp/Controller/Service/TCPRelay.cs:675

                EndPoint pluginEP = _controller.GetPluginLocalEndPointIfConfigured(_server);

                if (pluginEP != null)
                {
                    serverEP = pluginEP;
                    remote = new DirectConnect();
                }
                else if (_config.useProxy)
                {
                    switch (_config.proxyType)
                    {
                        case ForwardProxyConfig.PROXY_SOCKS5:
                            remote = new Socks5Proxy();
                            break;
                        case ForwardProxyConfig.PROXY_HTTP:
                            remote = new HttpProxy();
                            break;
                        default:
                            throw new NotSupportedException("Unknown forward proxy.");
                    }
                    proxyEP = SocketUtil.GetEndPoint(_config.proxyServer, _config.proxyPort);
                }
                else
                {
                    remote = new DirectConnect();
                }

                AsyncSession session = new AsyncSession(remote);
                lock (_closeConnLock)
                {
                    if (_closed)
                    {
                        remote.Close();
                        return;
                    }

                    _currentRemoteSession = session;

View on GitHub (pinned to 891d971682)

Solutions

1. Set proxyType to one of the supported constants (PROXY_SOCKS5 or PROXY_HTTP), or disable useProxy.
2. If you genuinely need a new proxy type, add a matching case + implementation before using it.
3. Validate proxyType against the known set when loading config and reject invalid values early with a clear message.

Example fix

// before
default:
    throw new NotSupportedException("Unknown forward proxy.");

// after: include the offending value
throw new NotSupportedException($"Unknown forward proxy type: {_config.proxyType}");

// Validate proxy type when loading config
if (config.useProxy &&
    config.proxyType != ForwardProxyConfig.PROXY_SOCKS5 &&
    config.proxyType != ForwardProxyConfig.PROXY_HTTP)
{ /* reset useProxy or clamp to a known type */ }

bool IsValidProxyType(string t) =>
    t == ForwardProxyConfig.PROXY_SOCKS5 || t == ForwardProxyConfig.PROXY_HTTP;

try { /* connect via forward proxy */ }
catch (NotSupportedException ex) when (ex.Message.Contains("Unknown forward proxy"))
{ /* disable useProxy, inform user */ }

When it happens

Trigger: A future/unknown proxyType constant was introduced without adding a case; gui-config.json was hand-edited and proxyType set to an invalid or typo'd value; an enum-like field stored as a string/int that deserialized to an unexpected value.

Common situations: Editing the config file and entering a wrong proxy type string; code merge that adds a new proxy type but forgets the switch case; corrupt config yielding an out-of-range integer.

Related errors

• Port out of range
• Port can't be 8123
• Password can not be blank
• Server IP can not be blank
• Timeout is invalid, it should not exceed {0}

AI-assisted analysis of shadowsocks/shadowsocks-windows@891d971682 (2026-08-13). Data as JSON: /api/errors/d0e746aab63947ee. Report an issue: GitHub.