Spring - server.connection-timeout not working

connection-timeout does not apply to long running requests. It does apply to the initial connection, when the server waits for the client to say something.

Tomcat docs (not Spring Boot) define it as The number of milliseconds this Connector will wait, after accepting a connection, for the request URI line to be presented [...]

To test the setting server.connection-timeout=4000 I connect using netcat and I don't send any HTTP request/headers. I get:

$ time nc -vv localhost 1234
Connection to localhost 1234 port [tcp/*] succeeded!

real    0m4.015s
user    0m0.000s
sys     0m0.000s

---

Alternatives

1) Async

From brightinventions.pl - Spring MVC Thread Pool Timeouts:

In Spring MVC there is no way to configure a timeout unless you use async method. With async method one can use spring.mvc.async.request-timeout= to set amount of time (in milliseconds) before asynchronous request handling times out.

I've set spring.mvc.async.request-timeout=4000 and I get a timeout in the browser with this:

@GetMapping("/test-async")
public Callable<String> getFoobar() {
   return () -> {
      Thread.sleep(12000); //this will cause a timeout
      return "foobar";
   };
}

See Spring Boot REST API - request timeout?

2) Servlet filter

Another solution would be to use a servlet filter brightinventions.pl - Request timeouts in Spring MVC (Kotlin):

override fun doFilterInternal(request: HttpServletRequest, response: HttpServletResponse, filterChain: FilterChain) {
    val completed = AtomicBoolean(false)
    val requestHandlingThread = Thread.currentThread()
    val timeout = timeoutsPool.schedule({
        if (completed.compareAndSet(false, true)) {
            requestHandlingThread.interrupt()
        }
    }, 5, TimeUnit.SECONDS)

    try {
        filterChain.doFilter(request, response)
        timeout.cancel(false)
    } finally {
        completed.set(true)
    }
}

3) Tomcat Stuck Thread Detection Valve?

Tomcat has a Stuck Thread Detection Valve but I don't know if this can be configured programmatically using Spring Boot.

From the official docs:

server.connection-timeout= # Time that connectors wait for another HTTP request before closing the connection. When not set, the connector's container-specific default is used. Use a value of -1 to indicate no (that is, an infinite) timeout.

Another ref, also mentions the same. It should work for you.

When I call the endpoint, the request never times out, it just hangs indefinitely.

server.connection-timeout isn't a request timeout. It is a timeout for idle connections, i.e. those that have already had a request/response pair and on which the server is now awaiting a second request. It is essentially a server-side read timeout.