Provide an option to start the server on a dynamic port

[ov7a]

Currently, it's mandatory to pass a valid free port.

It would be nice to have an option to omit the port, start with an ephemeral port provided by the OS.

Implementation-wise, it looks as simple as passing 0 to serverSocketFactory.createServerSocket(port) and exposing listenSocket.getLocalPort()

[bbottema]

Triaged this as still valid. Binding to port 0 already works at the socket layer, but the public API does not currently expose the chosen ephemeral port, so the usability part of this request remains open. The newer follow-up comment in this thread reflects the current implementation status on master.

[bbottema]

Started digging into this and pushed an initial implementation onto master.

Current status:

• SocksServer(0) can now rely on the OS for ephemeral port assignment
• callers can wait for startup with waitUntilStarted(...)
• callers can then read the chosen port via getListenPort()
• added a focused test covering the dynamic-port flow

This addresses the plain SocksServer API path discussed here. The remaining question is whether we also want a similar explicit bound-port lookup path on SyncSocksServer, or whether keeping the initial scope to SocksServer is enough.

[bbottema]

Implemented and pushed the handle-based API on master.

What is now available:

• RunningSocksServer, a small AutoCloseable handle exposing getPort() and stop()
• new SocksServer(0).startAndWait(timeoutMillis) for async SocksServer startup with actual bound-port discovery
• new SyncSocksServer().startServer(0) for synchronous startup with actual bound-port discovery
• multiple startServer(0) calls on one SyncSocksServer instance now return distinct listener handles
• stopping one returned handle leaves other active listeners running

Usage example:

try (RunningSocksServer server = new SyncSocksServer().startServer(0)) {
    int proxyPort = server.getPort();
    // use proxyPort in the test/client setup
}

Closing this as completed for the 4.2.0 milestone.

[ov7a]

Thank you! Worked like a charm for our scenario