Anuken/Mindustry · error · IOException

alreadyconnected

Error message

alreadyconnected

What it means

Net.connect rejects a second connection: if Net is already active (connected or hosting) it throws IOException 'alreadyconnected' rather than allowing overlapping connections. The client must disconnect first.

Solutions

1. Disconnect (Net.disconnect()) before connecting again.
2. Guard the call: check !Net.active() (and not hosting) first.
3. Debounce the connect UI action to prevent double-invocation.

Example fix

// before
Net.connect(ip, port, this::onConnected); // throws if already active

// after
if (!Net.active()) {
    Net.connect(ip, port, this::onConnected);
}

// Prevent overlapping connections.
if(Net.active()) {
    throw new IllegalStateException("Already connected/hosting; disconnect first.");
}
Net.connect(ip, port, success);

boolean canConnect(){ return !Net.active(); }

try {
    Net.connect(ip, port, success);
} catch(IOException e) {
    if("alreadyconnected".equals(e.getMessage())) { Net.disconnect(); Net.connect(ip, port, success); }
    else throw e;
}

When it happens

Trigger: Net.connect(ip, port, success) is called while Net.active is true (already connected or hosting).

Common situations: Double-clicking join; retrying connect without disconnect; joining while still closing a previous session; connect issued while hosting.

Related errors

• Invalid Steam ID
• Failed to parse server Steam ID
• Invalid Steam ID structure
• Cache file for asset
• Data must be exactly 32 bytes

AI-assisted analysis of Anuken/Mindustry@f695ad7e60 (2026-08-14). Data as JSON: /api/errors/19dc2d964cb50357. Report an issue: GitHub.

Appendix: source

Thrown at core/src/mindustry/net/Net.java:180

        active = true;
        server = false;
    }

    /**
     * Connect to an address.
     */
    public void connect(String ip, int port, Runnable success){
        streams.clear();
        currentStream = null;

        try{
            if(!active){
                Events.fire(new ClientServerConnectEvent(ip, port));
                provider.connectClient(ip, port, success);
                active = true;
                server = false;
            }else{
                throw new IOException("alreadyconnected");
            }
        }catch(IOException e){
            showError(e);
        }
    }

    /**
     * Host a server at an address.
     */
    public void host(int port) throws IOException{
        provider.hostServer(port);
        active = true;
        server = true;

        Time.runTask(60f, platform::updateRPC);
    }

    /**

View on GitHub (pinned to f695ad7e60)