webrtcice: Add webrtc ALPN header for HTTP proxy

Section 3.4 in RFC8835 states that if a WebRTC endpoint uses an HTTP
proxy to access the Internet it MUST include the "ALPN" header. This
commit adds this header.

By default the ALPN used when connecting to the TURN/TCP server via a
proxy is set to "webrtc". It can be changed by adding an alpn url
option for the http-proxy. For example:

http://user:pass@my.http.proxy.com:8080?alpn=c-webrtc

This will add the header "ALPN: c-webrtc" to the HTTP proxy CONNECT
request.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4212>

girs/GstWebRTC-1.0.gir

@@ -764,7 +764,7 @@ for more information.</doc>
         <source-position filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.h"/>
         <return-value transfer-ownership="full">
           <doc xml:space="preserve" filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.c">URI of the HTTP proxy of the form
-  http://[username:password@]hostname[:port]
+  http://[username:password@]hostname[:port][?alpn=&lt;alpn&gt;]
 
 Get HTTP Proxy to be used when connecting to TURN server.</doc>
           <type name="utf8" c:type="gchar*"/>
@@ -897,7 +897,7 @@ Get HTTP Proxy to be used when connecting to TURN server.</doc>
           </instance-parameter>
           <parameter name="uri" transfer-ownership="none">
             <doc xml:space="preserve" filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.c">URI of the HTTP proxy of the form
-  http://[username:password@]hostname[:port]</doc>
+  http://[username:password@]hostname[:port][?alpn=&lt;alpn&gt;]</doc>
             <type name="utf8" c:type="const gchar*"/>
           </parameter>
         </parameters>
@@ -1144,7 +1144,7 @@ Get HTTP Proxy to be used when connecting to TURN server.</doc>
         <source-position filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.h"/>
         <return-value transfer-ownership="full">
           <doc xml:space="preserve" filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.c">URI of the HTTP proxy of the form
-  http://[username:password@]hostname[:port]
+  http://[username:password@]hostname[:port][?alpn=&lt;alpn&gt;]
 
 Get HTTP Proxy to be used when connecting to TURN server.</doc>
           <type name="utf8" c:type="gchar*"/>
@@ -1287,7 +1287,7 @@ Get HTTP Proxy to be used when connecting to TURN server.</doc>
           </instance-parameter>
           <parameter name="uri" transfer-ownership="none">
             <doc xml:space="preserve" filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.c">URI of the HTTP proxy of the form
-  http://[username:password@]hostname[:port]</doc>
+  http://[username:password@]hostname[:port][?alpn=&lt;alpn&gt;]</doc>
             <type name="utf8" c:type="const gchar*"/>
           </parameter>
         </parameters>
@@ -1833,7 +1833,7 @@ stops automatic ICE gathering.</doc>
             </parameter>
             <parameter name="uri" transfer-ownership="none">
               <doc xml:space="preserve" filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.c">URI of the HTTP proxy of the form
-  http://[username:password@]hostname[:port]</doc>
+  http://[username:password@]hostname[:port][?alpn=&lt;alpn&gt;]</doc>
               <type name="utf8" c:type="const gchar*"/>
             </parameter>
           </parameters>
@@ -1844,7 +1844,7 @@ stops automatic ICE gathering.</doc>
           <source-position filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.h"/>
           <return-value transfer-ownership="full">
             <doc xml:space="preserve" filename="../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.c">URI of the HTTP proxy of the form
-  http://[username:password@]hostname[:port]
+  http://[username:password@]hostname[:port][?alpn=&lt;alpn&gt;]
 
 Get HTTP Proxy to be used when connecting to TURN server.</doc>
             <type name="utf8" c:type="gchar*"/>

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

@@ -237931,7 +237931,7 @@
                         "writable": false
                     },
                     "http-proxy": {
-                        "blurb": "A HTTP proxy for use with TURN/TCP of the form http://[username:password@]hostname[:port]",
+                        "blurb": "A HTTP proxy for use with TURN/TCP of the form http://[username:password@]hostname[:port][?alpn=<alpn>]",
                         "conditionally-available": false,
                         "construct": false,
                         "construct-only": false,

subprojects/gst-plugins-bad/ext/webrtc/gstwebrtcbin.c

@@ -8776,7 +8776,7 @@ gst_webrtc_bin_class_init (GstWebRTCBinClass * klass)
    * GstWebRTCBin:http-proxy:
    *
    * A HTTP proxy for use with TURN/TCP of the form
-   * http://[username:password@]hostname[:port]
+   * http://[username:password@]hostname[:port][?alpn=<alpn>]
    *
    * Since: 1.22
    */
@@ -8784,7 +8784,7 @@ gst_webrtc_bin_class_init (GstWebRTCBinClass * klass)
       PROP_HTTP_PROXY,
       g_param_spec_string ("http-proxy", "HTTP Proxy",
           "A HTTP proxy for use with TURN/TCP of the form "
-          "http://[username:password@]hostname[:port]",
+          "http://[username:password@]hostname[:port][?alpn=<alpn>]",
           NULL, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
   /**

subprojects/gst-plugins-bad/gst-libs/gst/webrtc/ice.c

@@ -458,7 +458,7 @@ gst_webrtc_ice_get_turn_server (GstWebRTCICE * ice)
  * gst_webrtc_ice_set_http_proxy:
  * @ice: The #GstWebRTCICE
  * @uri: (transfer none): URI of the HTTP proxy of the form
- *   http://[username:password@]hostname[:port]
+ *   http://[username:password@]hostname[:port][?alpn=<alpn>]
  *
  * Set HTTP Proxy to be used when connecting to TURN server.
  *
@@ -478,7 +478,7 @@ gst_webrtc_ice_set_http_proxy (GstWebRTCICE * ice, const gchar * uri_s)
  * @ice: The #GstWebRTCICE
  *
  * Returns: (transfer full): URI of the HTTP proxy of the form
- *   http://[username:password@]hostname[:port]
+ *   http://[username:password@]hostname[:port][?alpn=<alpn>]
  *
  * Get HTTP Proxy to be used when connecting to TURN server.
  *

subprojects/gst-plugins-bad/gst-libs/gst/webrtc/nice/nice.c

@@ -1351,8 +1351,10 @@ on_http_proxy_resolved (GstWebRTCICE * ice, GAsyncResult * res,
   const gchar *userinfo;
   gchar *user = NULL;
   gchar *pass = NULL;
+  const gchar *alpn = NULL;
   gchar *ip = NULL;
   guint port = GST_URI_NO_PORT;
+  GHashTable *extra_headers;
 
   if (!(addresses = resolve_host_finish (nice, res, &error))) {
     GST_WARNING_OBJECT (ice, "Failed to resolve http proxy: %s",
@@ -1382,13 +1384,23 @@ on_http_proxy_resolved (GstWebRTCICE * ice, GAsyncResult * res,
   userinfo = gst_uri_get_userinfo (uri);
   _parse_userinfo (userinfo, &user, &pass);
 
+  alpn = gst_uri_get_query_value (uri, "alpn");
+  if (!alpn) {
+    alpn = "webrtc";
+  }
+  extra_headers = g_hash_table_new_full (g_str_hash,
+      g_str_equal, g_free, g_free);
+  g_hash_table_insert (extra_headers, g_strdup ("ALPN"), g_strdup (alpn));
+
   g_object_set (nice->priv->nice_agent,
       "proxy-ip", ip, "proxy-port", port, "proxy-type", NICE_PROXY_TYPE_HTTP,
-      "proxy-username", user, "proxy-password", pass, NULL);
+      "proxy-username", user, "proxy-password", pass, "proxy-extra-headers",
+      extra_headers, NULL);
 
   g_free (ip);
   g_free (user);
   g_free (pass);
+  g_hash_table_unref (extra_headers);
 }
 
 static GstUri *