Previously, if an emulated TCP socket is connect()ed and one attempts to send() back to back right after connecting, the send would fail because the socket is not yet actually connected.

It is a bit hard to imagine where that behavior would be useful.

So this PR changes this behavior to be identical to how connectionless UDP sockets are emulated: instead, connect() calls are always pretended to succeed (since we cannot synchronously establish if the connect would fail, so presume it'll work), and all send() calls that are issued while the socket is connecting will be queued to be sent after the socket actually connects.

Author: juj

src/library_sockfs.js

@@ -241,7 +241,7 @@ addToLibrary({
           addr,
           port,
           socket: ws,
-          dgram_send_queue: []
+          msg_send_queue: []
         };
 
         SOCKFS.websocket_sock_ops.addPeer(sock, peer);
@@ -254,7 +254,7 @@ addToLibrary({
 #if SOCKET_DEBUG
           dbg('websocket queuing port message (port ' + sock.sport + ')');
 #endif
-          peer.dgram_send_queue.push(new Uint8Array([
+          peer.msg_send_queue.push(new Uint8Array([
               255, 255, 255, 255,
               'p'.charCodeAt(0), 'o'.charCodeAt(0), 'r'.charCodeAt(0), 't'.charCodeAt(0),
               ((sock.sport & 0xff00) >> 8) , (sock.sport & 0xff)
@@ -283,13 +283,13 @@ addToLibrary({
           Module['websocket'].emit('open', sock.stream.fd);
 
           try {
-            var queued = peer.dgram_send_queue.shift();
+            var queued = peer.msg_send_queue.shift();
             while (queued) {
 #if SOCKET_DEBUG
               dbg('websocket sending queued data (' + queued.byteLength + ' bytes): ' + [Array.prototype.slice.call(new Uint8Array(queued))]);
 #endif
               peer.socket.send(queued);
-              queued = peer.dgram_send_queue.shift();
+              queued = peer.msg_send_queue.shift();
             }
           } catch (e) {
             // not much we can do here in the way of proper error handling as we've already
@@ -493,8 +493,9 @@ addToLibrary({
         sock.daddr = peer.addr;
         sock.dport = peer.port;
 
-        // always "fail" in non-blocking mode
-        throw new FS.ErrnoError({{{ cDefs.EINPROGRESS }}});
+        // because we cannot synchronously block to wait for the WebSocket
+        // connection to complete, we return here pretending that the connection
+        // was a success.
       },
       listen(sock, backlog) {
         if (!ENVIRONMENT_IS_NODE) {
@@ -606,7 +607,9 @@ addToLibrary({
           if (!dest || dest.socket.readyState === dest.socket.CLOSING || dest.socket.readyState === dest.socket.CLOSED) {
             throw new FS.ErrnoError({{{ cDefs.ENOTCONN }}});
           } else if (dest.socket.readyState === dest.socket.CONNECTING) {
-            throw new FS.ErrnoError({{{ cDefs.EAGAIN }}});
+#if SOCKET_DEBUG
+            dbg('socket sendmsg called while socket is still connecting.');
+#endif
           }
         }
 
@@ -631,21 +634,21 @@ addToLibrary({
         }
 #endif
 
-        // if we're emulating a connection-less dgram socket and don't have
-        // a cached connection, queue the buffer to send upon connect and
-        // lie, saying the data was sent now.
-        if (sock.type === {{{ cDefs.SOCK_DGRAM }}}) {
-          if (!dest || dest.socket.readyState !== dest.socket.OPEN) {
-            // if we're not connected, open a new connection
+        // if we don't have a cached connectionless UDP datagram connection, or
+        // the TCP socket is still connecting, queue the message to be sent upon
+        // connect, and lie, saying the data was sent now.
+        if (!dest || dest.socket.readyState !== dest.socket.OPEN) {
+          // if we're not connected, open a new connection
+          if (sock.type === {{{ cDefs.SOCK_DGRAM }}}) {
             if (!dest || dest.socket.readyState === dest.socket.CLOSING || dest.socket.readyState === dest.socket.CLOSED) {
               dest = SOCKFS.websocket_sock_ops.createPeer(sock, addr, port);
             }
+          }
 #if SOCKET_DEBUG
-            dbg('websocket queuing (' + length + ' bytes): ' + [Array.prototype.slice.call(new Uint8Array(data))]);
+          dbg('websocket queuing (' + length + ' bytes): ' + [Array.prototype.slice.call(new Uint8Array(data))]);
 #endif
-            dest.dgram_send_queue.push(data);
-            return length;
-          }
+          dest.msg_send_queue.push(data);
+          return length;
         }
 
         try {

test/sockets/send_immediately_after_connect.cpp

@@ -0,0 +1,65 @@
+// This test verifies that calling send() back to back right after calling
+// connect() succeeds.
+
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <emscripten/html5.h>
+#include <string.h>
+#include <stdio.h>
+
+int sock;
+
+EM_BOOL wait_for_recv(double, void *) {
+  // Poll read from the socket to see what we have received
+  char buf[1024] = {};
+  recv(sock, buf, sizeof(buf)-1, 0);
+  if (strlen(buf) > 0)
+  {
+    printf("%s\n", buf);
+    if (!strcmp(buf, "Hello"))
+    {
+      printf("Got hello, test finished.\n");
+#ifdef REPORT_RESULT
+      REPORT_RESULT(0);
+#endif
+    }
+  }
+  return EM_TRUE;
+}
+
+int main() {
+  // Connect socket to a WebSocket echo server
+  sockaddr_in addr = {
+    .sin_family = AF_INET,
+    .sin_port = htons(8089)
+  };
+  inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr);
+  sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
+  if (sock < 0)
+  {
+    printf("socket() failed to error %d\n", sock);
+    return sock;    
+  }
+
+  // Connect to echo server.
+  int error = connect(sock, (sockaddr*)&addr, sizeof(addr));
+  if (error)
+  {
+    printf("connect() failed to error %d\n", error);
+    return error;
+  }
+
+  // Immediately send a message back-to-back from connecting to the socket
+  const char *msg = "Hello";
+  ssize_t bytes = send(sock, msg, strlen(msg), 0);
+  if (bytes != strlen(msg))
+  {
+    printf("send() failed to send %d bytes. Return value: %d\n", (int)strlen(msg), (int)bytes);
+    return bytes;
+  }
+
+  // Asynchronously wait until we get the message echoed back
+  emscripten_set_timeout_loop(wait_for_recv, 0, 0);
+  return 0;
+}

test/test_sockets.py

@@ -350,6 +350,11 @@ def test_posix_proxy_sockets(self):
         # Build and run the TCP echo client program with Emscripten
         self.btest_exit('websocket/tcp_echo_client.c', args=['-lwebsocket', '-sPROXY_POSIX_SOCKETS', '-pthread', '-sPROXY_TO_PTHREAD'])
 
+  # Test that multiple pthreads calling send() on the same socket produces correct ordering semantics.
+  def test_sockets_send_immediately_after_connect(self):
+    with NodeJsWebSocketEchoServerProcess():
+      self.btest('sockets/send_immediately_after_connect.cpp', args=['-DSOCKET_DEBUG'], expected='0')
+
 
 class sockets64(sockets):
   def setUp(self):