rtspsrc: use version template in user-agent property

Avoids documentation churn when the version changes.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5090>

subprojects/gst-plugins-good/docs/gst_plugins_cache.json

@@ -21628,7 +21628,7 @@
                         "construct": false,
                         "construct-only": false,
                         "controllable": false,
-                        "default": "GStreamer/1.23.0.1",
+                        "default": "GStreamer/{VERSION}",
                         "mutable": "null",
                         "readable": true,
                         "type": "gchararray",

subprojects/gst-plugins-good/gst-libs/gst/glib-compat-private.h

@@ -29,6 +29,53 @@ G_BEGIN_DECLS
 
 /* copies */
 
+#if !GLIB_CHECK_VERSION(2,68,0)
+#ifndef g_string_replace
+#define g_string_replace gst_g_string_replace
+#endif
+
+static inline guint
+gst_g_string_replace (GString     *string,
+                      const gchar *find,
+                      const gchar *replace,
+                      guint        limit)
+{
+  gsize f_len, r_len, pos;
+  gchar *cur, *next;
+  guint n = 0;
+
+  g_return_val_if_fail (string != NULL, 0);
+  g_return_val_if_fail (find != NULL, 0);
+  g_return_val_if_fail (replace != NULL, 0);
+
+  f_len = strlen (find);
+  r_len = strlen (replace);
+  cur = string->str;
+
+  while ((next = strstr (cur, find)) != NULL)
+    {
+      pos = next - string->str;
+      g_string_erase (string, pos, f_len);
+      g_string_insert (string, pos, replace);
+      cur = string->str + pos + r_len;
+      n++;
+      /* Only match the empty string once at any given position, to
+       * avoid infinite loops */
+      if (f_len == 0)
+        {
+          if (cur[0] == '\0')
+            break;
+          else
+            cur++;
+        }
+      if (n == limit)
+        break;
+    }
+
+  return n;
+}
+#endif /* GLIB_CHECK_VERSION */
+
 /* adaptations */
 
 G_END_DECLS

subprojects/gst-plugins-good/gst/rtsp/gstrtspsrc.c

@@ -117,6 +117,8 @@
 #include "gstrtspelements.h"
 #include "gstrtspsrc.h"
 
+#include <gst/glib-compat-private.h>
+
 GST_DEBUG_CATEGORY_STATIC (rtspsrc_debug);
 #define GST_CAT_DEFAULT (rtspsrc_debug)
 
@@ -299,7 +301,7 @@ gst_rtsp_backchannel_get_type (void)
 #define DEFAULT_TLS_INTERACTION     NULL
 #define DEFAULT_DO_RETRANSMISSION        TRUE
 #define DEFAULT_NTP_TIME_SOURCE  NTP_TIME_SOURCE_NTP
-#define DEFAULT_USER_AGENT       "GStreamer/" PACKAGE_VERSION
+#define DEFAULT_USER_AGENT       "GStreamer/{VERSION}"
 #define DEFAULT_MAX_RTCP_RTP_TIME_DIFF 1000
 #define DEFAULT_RFC7273_SYNC         FALSE
 #define DEFAULT_ADD_REFERENCE_TIMESTAMP_META FALSE
@@ -895,6 +897,9 @@ gst_rtspsrc_class_init (GstRTSPSrcClass * klass)
    *
    * The string to set in the User-Agent header.
    *
+   * If the string contains `{VERSION}` that will be replaced with the
+   * GStreamer version at runtime (since GStreamer 1.24).
+   *
    * Since: 1.6
    */
   g_object_class_install_property (gobject_class, PROP_USER_AGENT,
@@ -5467,8 +5472,13 @@ gst_rtspsrc_init_request (GstRTSPSrc * src, GstRTSPMessage * msg,
     return res;
 
   /* set user-agent */
-  if (src->user_agent)
+  if (src->user_agent) {
-    gst_rtsp_message_add_header (msg, GST_RTSP_HDR_USER_AGENT, src->user_agent);
+    GString *user_agent = g_string_new (src->user_agent);
+
+    g_string_replace (user_agent, "{VERSION}", PACKAGE_VERSION, 0);
+    gst_rtsp_message_add_header (msg, GST_RTSP_HDR_USER_AGENT, user_agent->str);
+    g_string_free (user_agent, TRUE);
+  }
 
   return res;
 }