Why OkHttp doesn't reuse its connections?

Question

I'm performing an http-benchmark using OkHttp 3.5.0. I'm sending thousands of requests to the same URL.

I expect that the OkHttp-client uses a ConnectionPool and reuses its connections over and over. But if we look into netstat we'll see many connections in the TIME_WAIT state:

TCP    127.0.0.1:80           127.0.0.1:51752        TIME_WAIT
TCP    127.0.0.1:80           127.0.0.1:51753        TIME_WAIT
TCP    127.0.0.1:80           127.0.0.1:51754        TIME_WAIT
TCP    127.0.0.1:80           127.0.0.1:51755        TIME_WAIT
TCP    127.0.0.1:80           127.0.0.1:51756        TIME_WAIT
...

After a couple of thousands of requests I'm getting a SocketException: No buffer space available (maximum connections reached?)

The code preforming requests (Kotlin):

val client = OkHttpClient.Builder()
        .connectionPool(ConnectionPool(5, 1, TimeUnit.MINUTES))
        .build()

val request = Request.Builder().url("http://192.168.0.50").build()

while (true) {
    val response = client.newCall(request).execute()
    response.close()
}

If instead of response.close() I use response.body().string(), then SocketException doesn't happen, but netstat still shows plenty of TIME_WAIT connections, and the benchmark performance is getting lower and lower.

What am I doing wrong?

PS: I've tried to use Apache HttpClient and its PoolingHttpClientConnectionManager, and seems like it works perfectly. But I'd like to figure out what's wrong with OkHttp.

Answer 1

my version is 3.13.0, which is not too far from 3.5.0 and i meet TIME_WAIT problem too.

after dive into source code, i found in CallServerInterceptor.java line 142:

if ("close".equalsIgnoreCase(response.request().header("Connection"))
    || "close".equalsIgnoreCase(response.header("Connection"))) {
   streamAllocation.noNewStreams();
}

and in StreamAllocation.java line 367:

public void noNewStreams() {
    Socket socket;
    Connection releasedConnection;
    synchronized (connectionPool) {
      releasedConnection = connection;
      socket = deallocate(true, false, false); // close connection!
      if (connection != null) releasedConnection = null;
    }
    closeQuietly(socket);
    if (releasedConnection != null) {
      eventListener.connectionReleased(call, releasedConnection);
    }
}

which means okhttp will CLOSE connection if "Connection: close" header exists in either request or response

although long time passed since question been submit, i hope this answer help guys who encountering this problem, good luck.

Answer 2

Thanks to toien and I find my solution (for a non-standard http server).

public class Http1CodecWrapper implements HttpCodec {
    private HttpCodec codec;

    public Http1CodecWrapper(HttpCodec codec) {
        this.codec = codec;
    }

    // ...

    @Override
    public Response.Builder readResponseHeaders(boolean expectContinue) throws IOException {
        return codec.readResponseHeaders(expectContinue)
            .addHeader("Connection", "keep-alive");
    }
}

OkHttpClient httpClient = new OkHttpClient.Builder()
    .addNetworkInterceptor(new Interceptor() {
            @Override
            public Response intercept(Chain chain) throws IOException {
                RealInterceptorChain realChain = (RealInterceptorChain) chain;
                Request request = realChain.request();
                StreamAllocation allocation = realChain.streamAllocation();
                HttpCodec codec = new Http1CodecWrapper(realChain.httpStream());
                RealConnection connection = (RealConnection) realChain.connection();

                return realChain.proceed(request, allocation, codec, connection);
            }
        })
    .build();