test: ensure HTTPServer race condition is fixed

The result of WriteReply() losing the race condition would prevent any
new requests being read from the socket. The socket error test
sent 3 requests all at once after connecting, so in this commit
we separate the the third request to make the losing race
condition more likely, and make its effect more obvious.

src/test/httpserver_tests.cpp

@@ -697,7 +697,7 @@ BOOST_AUTO_TEST_CASE(http_socket_error_tests)
     server.StartSocketsThreads();
 
     // Prepare initial requests
-    int num_requests = 3;
+    int num_requests = 2;
     // Use keep-alive so the server holds the connection open for all requests.
     std::string keepalive_request{full_request};
     keepalive_request.replace(keepalive_request.find("Connection: close"), 17, "Connection: keep-alive");
@@ -730,7 +730,34 @@ BOOST_AUTO_TEST_CASE(http_socket_error_tests)
     // Wait up to one minute for the last reply from the server
     std::string actual;
     char buf[0x10000] = {};
-    int attempts = 1000;
+    int attempts = 6000;
+    while (attempts > 0)
+    {
+        ssize_t bytes_read = mock_client_socket_pipes->send.GetBytes(buf, sizeof(buf), 0);
+        if (bytes_read > 0) {
+            actual.append(buf, bytes_read);
+            if (actual.find(strprintf("height: %d", num_requests - 1)) != std::string::npos) {
+                break;
+            }
+        }
+        std::this_thread::sleep_for(10ms);
+        --attempts;
+    }
+
+    // Send the third request.
+    // If there was a race between WriteReply() in the worker thread setting m_send_ready=true
+    // and SocketHandlerConnected() in the I/O thread flushing the send buffer,
+    // then the socket would be stuck in write mode with nothing to write,
+    // the server would never read from the socket, and this request would time out.
+    // Wait a second to ensure both the worker thread and I/O thread are idle.
+    // If we send the next request too soon it might get accepted by the server before
+    // it gets wedged shut.
+    std::this_thread::sleep_for(1000ms);
+    mock_client_socket_pipes->recv.PushBytes(keepalive_request.data(), keepalive_request.size());
+    num_requests++;
+
+    // Wait up to one minute for reply
+    attempts = 6000;
     while (attempts > 0)
     {
         ssize_t bytes_read = mock_client_socket_pipes->send.GetBytes(buf, sizeof(buf), 0);