From 202c4c9067b5855295895eed8c06fcb64c54e260 Mon Sep 17 00:00:00 2001
From: Adam Scott <ascott.ca@gmail.com>
Date: Thu, 24 Apr 2025 22:46:52 -0400
Subject: [PATCH] Fix `sendmsg()` implementation

---
 src/lib/libsockfs.js                          |  2 +-
 .../test_sockets_sendmsg_to_invalid_dest.c    | 68 +++++++++++++++++++
 test/test_sockets.py                          |  4 ++
 3 files changed, 73 insertions(+), 1 deletion(-)
 create mode 100644 test/sockets/test_sockets_sendmsg_to_invalid_dest.c

diff --git a/src/lib/libsockfs.js b/src/lib/libsockfs.js
index 786606c3c39bc..203088fbaa489 100644
--- a/src/lib/libsockfs.js
+++ b/src/lib/libsockfs.js
@@ -632,7 +632,7 @@ addToLibrary({
         // 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 || 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);
             }
diff --git a/test/sockets/test_sockets_sendmsg_to_invalid_dest.c b/test/sockets/test_sockets_sendmsg_to_invalid_dest.c
new file mode 100644
index 0000000000000..57120edfdb604
--- /dev/null
+++ b/test/sockets/test_sockets_sendmsg_to_invalid_dest.c
@@ -0,0 +1,68 @@
+// Copyright 2025 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <arpa/inet.h>
+#include <emscripten.h>
+#include <emscripten/eventloop.h>
+#include <ifaddrs.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int sock;
+
+bool wait_for_recv(double d, void* u) {
+  // 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
+  struct 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, (struct 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;
+  }
+
+  // This shouldn't throw an exception in `sendmsg` implementation.
+  // [see GH-23046]
+  struct ifaddrs* ifaddrs = NULL;
+  getifaddrs(&ifaddrs);
+
+  // Asynchronously wait until we get the message echoed back
+  emscripten_set_timeout_loop(wait_for_recv, 0, 0);
+  return 0;
+}
diff --git a/test/test_sockets.py b/test/test_sockets.py
index 9f21a4f870463..e23e6094b2379 100644
--- a/test/test_sockets.py
+++ b/test/test_sockets.py
@@ -359,6 +359,10 @@ def test_sockets_send_while_connecting(self):
     with NodeJsWebSocketEchoServerProcess():
       self.btest('sockets/test_sockets_send_while_connecting.c', emcc_args=['-DSOCKET_DEBUG'], expected='0')
 
+  def test_sockets_sendmsg_to_invalid_dest(self):
+    with NodeJsWebSocketEchoServerProcess():
+      self.btest('sockets/test_sockets_sendmsg_to_invalid_dest.c', emcc_args=['-DSOCKET_DEBUG', '-lsockfs.js'], expected='0')
+
 
 class sockets64(sockets):
   def setUp(self):