[NODERAWSOCKETS] Bind-first connect for synchronous getsockname

src/lib/libsockfs_node.js

@@ -22,8 +22,10 @@
 // net.BoundSocket when the runtime offers it, else the private tcp_wrap binding
 // as a fallback (net.Server's listen is async and cannot report an assigned
 // ephemeral port up front, so it can't drive bind on its own). connect() goes
-// through net.Socket, adopting the bound handle when one exists so an explicit
-// source address/port is honored, and otherwise letting the kernel assign one.
+// through net.Socket, adopting the bound handle so an explicit source
+// address/port is honored; an unbound client binds an ephemeral port first,
+// since the kernel assigns the source port synchronously at connect() and
+// getsockname() must report it immediately.
 //
 // UDP uses the public node:dgram socket when it exposes a synchronous bindSync
 // (a recent node addition that ships alongside connectSync), giving the
@@ -573,15 +575,16 @@ var NodeSockFSLibrary = {
       sock.dport = port;
       sock.state = {{{ SOCK_STATE_CONNECTING }}};
       var net = nodeSockHelpers.getNet();
-      var conn;
-      if (sock.bound) {
-        // A prior bind() produced a real, already-bound handle; connect through
-        // it so the bound source address/port is honored by the kernel.
-        conn = new net.Socket({ handle: sock.bound, pauseOnCreate: true, allowHalfOpen: true });
-      } else {
-        // Unbound client: let the kernel assign the source address/port.
-        conn = new net.Socket({ allowHalfOpen: true });
-      }
+      if (!sock.bound) {
+        // The kernel assigns the ephemeral source port synchronously at
+        // connect(), so an unbound client binds an ephemeral port first (the
+        // same eager bindHandle path an explicit bind() takes) and getsockname()
+        // is correct immediately, not only once the async connect completes.
+        nodeSockHelpers.bindHandle(sock, addr.includes(':') ? '::' : '0.0.0.0', 0);
+      }
+      // Connect through the bound handle so the bound source address/port is
+      // honored by the kernel.
+      var conn = new net.Socket({ handle: sock.bound, pauseOnCreate: true, allowHalfOpen: true });
       conn.once('connect', () => {
         sock.state = {{{ SOCK_STATE_CONNECTED }}};
         sock.saddr = conn.localAddress;

test/sockets/test_tcp_connect_getsockname.c

@@ -0,0 +1,151 @@
+/*
+ * Copyright 2026 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.
+ *
+ * getsockname() immediately after a non-blocking connect() on an unbound
+ * client must report the kernel-assigned ephemeral source port: the kernel
+ * assigns it synchronously at connect(), not when the connection completes.
+ * The port must then stay the same once connected. This is plain POSIX and
+ * also builds and runs natively, so the same code can be checked against the
+ * host stack.
+ */
+
+#include <arpa/inet.h>
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <netinet/in.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <unistd.h>
+
+#ifdef __EMSCRIPTEN__
+#include <emscripten.h>
+#endif
+
+int listen_fd = -1;
+int client_fd = -1;
+int peer_fd = -1;
+struct sockaddr_in dest;
+bool connected = false;
+uint16_t client_port = 0; // network order, recorded right after connect()
+
+void set_nonblocking(int fd) {
+  fcntl(fd, F_SETFL, O_NONBLOCK);
+}
+
+void test_success(void) {
+  printf("done\n");
+  if (listen_fd >= 0) close(listen_fd);
+  if (client_fd >= 0) close(client_fd);
+  if (peer_fd >= 0) close(peer_fd);
+#ifdef __EMSCRIPTEN__
+  emscripten_cancel_main_loop();
+#else
+  exit(0);
+#endif
+}
+
+void start_client(void) {
+  if (client_fd >= 0) close(client_fd);
+  client_fd = socket(AF_INET, SOCK_STREAM, 0);
+  assert(client_fd >= 0);
+  set_nonblocking(client_fd);
+  connected = false;
+  int r = connect(client_fd, (struct sockaddr*)&dest, sizeof(dest));
+  assert((r == 0 || errno == EINPROGRESS) && "connect");
+
+  // The ephemeral source port is assigned synchronously at connect(): it must
+  // be visible here, before the connection completes or any event turn runs.
+  struct sockaddr_in sa;
+  socklen_t sl = sizeof(sa);
+  int g = getsockname(client_fd, (struct sockaddr*)&sa, &sl);
+  assert(g == 0 && "getsockname after connect");
+  assert(ntohs(sa.sin_port) != 0 && "ephemeral port assigned at connect()");
+  client_port = sa.sin_port;
+  printf("connecting from port %u\n", (unsigned)ntohs(client_port));
+}
+
+void main_loop(void) {
+  fd_set fdr, fdw;
+  struct timeval tv = {0};
+  FD_ZERO(&fdr);
+  FD_ZERO(&fdw);
+  FD_SET(listen_fd, &fdr);
+  FD_SET(client_fd, &fdw);
+  select(64, &fdr, &fdw, NULL, &tv);
+
+  if (peer_fd < 0 && FD_ISSET(listen_fd, &fdr)) {
+    peer_fd = accept(listen_fd, NULL, NULL);
+    if (peer_fd >= 0) set_nonblocking(peer_fd);
+  }
+
+  if (!connected && FD_ISSET(client_fd, &fdw)) {
+    int err = 0;
+    socklen_t l = sizeof(err);
+    getsockopt(client_fd, SOL_SOCKET, SO_ERROR, &err, &l);
+    if (err == ECONNREFUSED || err == ECONNRESET) {
+      start_client();
+      return;
+    }
+    assert(err == 0 && "connect failed");
+    connected = true;
+
+    // The name must not change when the connection completes.
+    struct sockaddr_in sa;
+    socklen_t sl = sizeof(sa);
+    assert(getsockname(client_fd, (struct sockaddr*)&sa, &sl) == 0);
+    assert(sa.sin_port == client_port && "port stable across connect completion");
+    test_success();
+  }
+}
+
+int main(void) {
+  listen_fd = socket(AF_INET, SOCK_STREAM, 0);
+  assert(listen_fd >= 0);
+
+  struct sockaddr_in addr;
+  memset(&addr, 0, sizeof(addr));
+  addr.sin_family = AF_INET;
+  addr.sin_port = htons(0);
+  inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr);
+  if (bind(listen_fd, (struct sockaddr*)&addr, sizeof(addr)) != 0) {
+    perror("bind");
+    return 1;
+  }
+  if (listen(listen_fd, 4) != 0) {
+    perror("listen");
+    return 1;
+  }
+
+  struct sockaddr_in la;
+  socklen_t ll = sizeof(la);
+  if (getsockname(listen_fd, (struct sockaddr*)&la, &ll) != 0) {
+    perror("getsockname");
+    return 1;
+  }
+  set_nonblocking(listen_fd);
+
+  memset(&dest, 0, sizeof(dest));
+  dest.sin_family = AF_INET;
+  dest.sin_port = la.sin_port;
+  inet_pton(AF_INET, "127.0.0.1", &dest.sin_addr);
+  start_client();
+
+#ifdef __EMSCRIPTEN__
+  emscripten_set_main_loop(main_loop, 0, 0);
+#else
+  while (1) {
+    main_loop();
+    usleep(1000);
+  }
+#endif
+  return 0;
+}

test/test_sockets_node.py

@@ -126,6 +126,12 @@ def test_noderawsockets_client_bind(self):
       server.server_close()
       thread.join()
 
+  def test_noderawsockets_connect_getsockname(self):
+    # getsockname() immediately after a non-blocking connect() on an unbound
+    # client reports the ephemeral source port synchronously (kernel semantics:
+    # the port is assigned at connect(), not when the connection completes).
+    self.do_runf('sockets/test_tcp_connect_getsockname.c', 'done\n', cflags=['-sNODERAWSOCKETS'])
+
   def test_noderawsockets_client_semantics(self):
     # EISCONN on a second connect, shutdown(SHUT_WR) leaving reads working,
     # EPIPE on a write after that, and POLLHUP after a full shutdown(SHUT_RDWR).