udpsclient: a TCP transport mode (SUBSCRIBE, no CONNECT) and a TCP mock server

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deps/udpsclient/udps_client.c

@@ -174,6 +174,7 @@ struct udps_client {
     char server_addr[128];
     char mcast_group[128];
     char iface_addr[128];
+    char stream_name[256];
 
     struct sockaddr_in server_sa;
     int    udp_fd;   /**< Unicast receive socket, or joined multicast socket. */
@@ -1149,9 +1150,50 @@ static int connect_multicast(udps_client_t *c) {
     return 0;
 }
 
+/** TCP transport: connect, then SUBSCRIBE when a stream name is set. */
+static int connect_tcp(udps_client_t *c) {
+    struct timeval tv;
+    size_t         name_len = strlen(c->stream_name);
+
+    c->tcp_fd = socket(AF_INET, SOCK_STREAM, 0);
+    if (c->tcp_fd < 0) {
+        return fail(c, "TCP socket() failed: %s", strerror(errno));
+    }
+    set_recv_buffer(c->tcp_fd, c->cfg.recv_buffer_bytes);
+    /* Linux bounds a blocking connect() with SO_SNDTIMEO, so an unreachable host
+     * cannot hold the polling thread for minutes. */
+    tv.tv_sec  = 3;
+    tv.tv_usec = 0;
+    (void)setsockopt(c->tcp_fd, SOL_SOCKET, SO_SNDTIMEO, &tv, (socklen_t)sizeof tv);
+    if (connect(c->tcp_fd, (struct sockaddr *)&c->server_sa,
+                (socklen_t)sizeof c->server_sa) != 0) {
+        int e = errno;
+        close_sockets(c);
+        return fail(c, "TCP connect to %s:%u failed: %s", c->server_addr,
+                    (unsigned)c->cfg.server_port, strerror(e));
+    }
+    /* A half-received frame must not wedge the poll loop (read_exact_tcp blocks). */
+    tv.tv_sec = 1;
+    (void)setsockopt(c->tcp_fd, SOL_SOCKET, SO_RCVTIMEO, &tv, (socklen_t)sizeof tv);
+
+    if (name_len > 0u) {
+        uint8_t pkt[UDPS_HEADER_SIZE + 255u];
+        build_header(pkt, UDPS_PKT_SUBSCRIBE, 0u, 0u, 1u, (uint32_t)name_len);
+        memcpy(pkt + UDPS_HEADER_SIZE, c->stream_name, name_len);
+        if (send(c->tcp_fd, pkt, UDPS_HEADER_SIZE + name_len, MSG_NOSIGNAL) !=
+            (ssize_t)(UDPS_HEADER_SIZE + name_len)) {
+            int e = errno;
+            close_sockets(c);
+            return fail(c, "SUBSCRIBE failed: %s", strerror(e));
+        }
+    }
+    return 0;
+}
+
 static int do_connect(udps_client_t *c) {
-    int rc = (c->mcast_group[0] != '\0') ? connect_multicast(c)
-                                         : connect_unicast(c);
+    int rc = c->cfg.use_tcp ? connect_tcp(c)
+             : (c->mcast_group[0] != '\0') ? connect_multicast(c)
+                                           : connect_unicast(c);
     if (rc != 0) {
         c->disconnect_t = now_mono();
         return rc;
@@ -1174,7 +1216,10 @@ static void do_disconnect(udps_client_t *c, const char *why) {
     if (!c->connected) {
         return;
     }
-    (void)send_control(c, UDPS_PKT_DISCONNECT);
+    if (!c->cfg.use_tcp) {
+        /* TCP: a write to a peer that closed would raise SIGPIPE; the server sees the close itself. */
+        (void)send_control(c, UDPS_PKT_DISCONNECT);
+    }
     close_sockets(c);
     c->connected    = 0;
     c->disconnect_t = now_mono();
@@ -1267,17 +1312,28 @@ udps_client_t *udps_client_create(const udps_client_config_t *cfg) {
     if (c == NULL) {
         return NULL;
     }
+    if (cfg->use_tcp && cfg->stream_name != NULL && strlen(cfg->stream_name) > 255u) {
+        free(c);
+        return NULL;
+    }
     c->cfg    = *cfg;
     c->udp_fd = -1;
     c->tcp_fd = -1;
     copy_str(c->server_addr, sizeof c->server_addr, cfg->server_addr);
     copy_str(c->mcast_group, sizeof c->mcast_group, cfg->multicast_group);
     copy_str(c->iface_addr, sizeof c->iface_addr, cfg->interface_addr);
+    copy_str(c->stream_name, sizeof c->stream_name, cfg->stream_name);
     /* The config's string pointers must not be used again: they belong to the
      * caller and the copies above are what the client works from. */
     c->cfg.server_addr     = c->server_addr;
     c->cfg.multicast_group = (c->mcast_group[0] != '\0') ? c->mcast_group : NULL;
     c->cfg.interface_addr  = (c->iface_addr[0] != '\0') ? c->iface_addr : NULL;
+    c->cfg.stream_name     = c->stream_name;
+    if (c->cfg.use_tcp) {
+        c->cfg.multicast_group  = NULL;
+        c->mcast_group[0]       = '\0';
+        c->cfg.reorder_window_s = 0.0;
+    }
 
     if (c->cfg.max_packet_bytes == 0u) {
         c->cfg.max_packet_bytes = 1u * 1024u * 1024u;