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.h

@@ -52,7 +52,8 @@ enum {
     UDPS_PKT_CONFIG     = 1, /**< Server -> client: signal metadata. */
     UDPS_PKT_ACK        = 2, /**< Client -> server: keepalive. */
     UDPS_PKT_CONNECT    = 3, /**< Client -> server: open a session. */
-    UDPS_PKT_DISCONNECT = 4  /**< Either direction: close a session. */
+    UDPS_PKT_DISCONNECT = 4, /**< Either direction: close a session. */
+    UDPS_PKT_SUBSCRIBE  = 5  /**< Client -> server (TCP stream service): payload = stream name. */
 };
 
 /** Sample type codes (udps_signal_t::type_code). */
@@ -279,6 +280,20 @@ typedef struct {
      * the drop-on-late behaviour. Default 0.020.
      */
     double      reorder_window_s;
+    /**
+     * Non-zero selects the TCP transport (a MARTe2 TCPStreamer / TCPStreamService):
+     * @c server_port is the TCP port, no CONNECT or DISCONNECT frame is sent, the
+     * server streams CONFIG then DATA on connect, and the reorder window is forced
+     * to 0 (TCP is ordered, so a counter gap is a server-side drop). @c multicast_group,
+     * @c interface_addr and @c data_port are ignored.
+     */
+    int         use_tcp;
+    /**
+     * TCP mode only: when non-empty (1..255 bytes) a SUBSCRIBE frame naming this stream is
+     * sent right after every connect, as a TCPStreamService requires. A plain
+     * TCPStreamer ignores it. NULL or "" sends nothing.
+     */
+    const char *stream_name;
 } udps_client_config_t;
 
 /** Fills @p cfg with the defaults documented in Docs/UDPS-C-Client.md. */