Having trouble getting to the bottom of why my test fails with SocketTimeoutException unless I remove Expect 100-continue header. Any ideas?

java.net.SocketTimeoutException: Read timed out at java.net.SocketInputStream.socketRead0(Native Method) at java.net.SocketInputStream.read(SocketInputStream.java:152) at java.net.SocketInputStream.read(SocketInputStream.java:122) at java.io.BufferedInputStream.fill(BufferedInputStream.java:235) at java.io.BufferedInputStream.read1(BufferedInputStream.java:275) at java.io.BufferedInputStream.read(BufferedInputStream.java:334) at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:677) at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:623) at sun.net.www.protocol.http.HttpURLConnection.expect100Continue(HttpURLConnection.java:1020) at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:1105)

Code:

public void testExpect100() throws Exception {
    MockWebServer server = new MockWebServer();
    server.enqueue(new MockResponse().setBody("hello world"));
    server.play();

    URL url = server.getUrl("/");
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    connection.setConnectTimeout(1000);
    connection.setReadTimeout(1000);
    connection.setAllowUserInteraction(false);
    connection.setRequestMethod("POST");
    connection.setRequestProperty("Expect", "100-continue"); // << comment this and it will pass
    connection.setRequestProperty(CONTENT_LENGTH, "4");
    connection.setFixedLengthStreamingMode(4);
    connection.setDoOutput(true);
    connection.getOutputStream().write(new byte [] {1, 2, 3, 4});

    InputStream in = connection.getInputStream();
    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
    assertEquals(HttpURLConnection.HTTP_OK, connection.getResponseCode());
    assertEquals("hello world", reader.readLine());

    RecordedRequest request = server.takeRequest();
    assertEquals("POST / HTTP/1.1", request.getRequestLine());
}

this is annoying and the fault of the java impl. In looking at the stack inside sun.net, there's goofy timeout logic when expect100Continue is used. A workaround is to change my test case to explicitly set read timeout to zero. I'm fine with the workaround, so feel free to take action or close this out.

    connection.setReadTimeout(0);

The workaround for this (setting the read timeout to 0) causes empty PUTs to hang: issue 8