[Openvpn-devel,3/4] options: add support for --transport-plugin

diff --git a/doc/openvpn.8 b/doc/openvpn.8
index 7abcaf1e..9325dabd 100644
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -2847,6 +2847,46 @@  every module and script must return success (0) in order for
 the connection to be authenticated.
 .\"*********************************************************
 .TP
+.B \-\-transport-plugin module-pathname [connection-args]
+Use the loaded plugin module identified by
+.B module-pathname
+to provide a transport layer for the connection. The
+.B module-pathname
+must be exactly equivalent to a pathname supplied to a
+.B \-\-plugin
+option. The same transport plugin may be used for
+multiple connections, in which case the
+.B \-\-plugin
+option which loads it should only occur once. However,
+only one transport plugin may be specified per
+connection.
+
+If
+.B connection-args
+are present, these arguments are passed to the transport
+plugin when establishing this connection specifically; this
+is distinct from any per-plugin arguments which may have
+been specified using the
+.B \-\-plugin
+option. Documentation for possible
+.B connection-args
+may be provided along with the plugin in use.
+
+When a transport plugin is in use, the
+.B \-\-proto
+option should not normally be used and will usually result in
+an error, as the transport plugin takes over from the native
+transport protocol that would otherwise be specified. The
+rest of OpenVPN will operate in a manner similar to that of
+UDP mode, using the pseudo-protocol "indirect". There is one
+remaining rare use for
+.B \-\-proto
+in this case, which is to force a specific address family for
+transport plugins for which this is still meaningful. This can
+be done by specifying "indirect4" or "indirect6" as the
+protocol.
+.\"*********************************************************
+.TP
 .B \-\-keying\-material\-exporter label len
 Save Exported Keying Material [RFC5705] of len bytes (must be
 between 16 and 4095 bytes) using label in environment
diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 560d87db..9f7b5fdd 100644
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -3335,6 +3335,7 @@  do_init_socket_1(struct context *c, const int mode)
                             &c->c1.link_socket_addr,
                             c->options.ipchange,
                             c->plugins,
+                            c->options.ce.transport_plugin_argv,
                             c->options.resolve_retry_seconds,
                             c->options.ce.mtu_discover_type,
                             c->options.rcvbuf,
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 0cf8db76..7e905532 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -403,6 +403,9 @@  static const char usage_message[] =
 #ifdef ENABLE_PLUGIN
     "--plugin m [str]: Load plug-in module m passing str as an argument\n"
     "                  to its initialization function.\n"
+    "--transport-plugin m [args]: Use plug-in module m to provide the transport\n"
+    "                             layer, with optional per-connection args. The\n"
+    "                             module must already be loaded with --plugin.\n"
 #endif
 #if P2MP
 #if P2MP_SERVER
@@ -2005,6 +2008,22 @@  options_postprocess_verify_ce(const struct options *options, const struct connec
         msg(M_USAGE, "--proto tcp is ambiguous in this context.  Please specify --proto tcp-server or --proto tcp-client");
     }
 
+#ifdef ENABLE_PLUGIN
+    /*
+     * "proto indirect" may not be specified directly without a
+     * transport-plugin, and vice versa.
+     */
+    if (ce->proto == PROTO_INDIRECT && !ce->transport_plugin_argv)
+    {
+        msg(M_USAGE, "--proto indirect may not be used without a transport-plugin line");
+    }
+
+    if (ce->transport_plugin_argv && ce->proto != PROTO_INDIRECT)
+    {
+        msg(M_USAGE, "--transport-plugin must be used with --proto indirect");
+    }
+#endif
+
     /*
      * Sanity check on daemon/inetd modes
      */
@@ -5190,6 +5209,18 @@  add_option(struct options *options,
             goto err;
         }
     }
+    else if (streq(p[0], "transport-plugin") && p[1])
+    {
+        VERIFY_PERMISSION(OPT_P_PLUGIN|OPT_P_CONNECTION);
+
+        /* p[1] is the shared object name, which becomes
+         * argv[0]. p[2..] are connection-specific transport
+         * parameters, which become argv[1..].
+         */
+        options->ce.transport_plugin_argv = make_extended_arg_array(&p[1],
+                                                                    &options->gc);
+        options->ce.proto = PROTO_INDIRECT;
+    }
 #endif
     else if (streq(p[0], "mode") && p[1] && !p[2])
     {
diff --git a/src/openvpn/options.h b/src/openvpn/options.h
index e2b38939..c2d0e9ac 100644
--- a/src/openvpn/options.h
+++ b/src/openvpn/options.h
@@ -85,6 +85,7 @@  struct options_pre_pull
 
 struct connection_entry
 {
+    const char **transport_plugin_argv;
     int proto;
     sa_family_t af;
     const char *local_port;
diff --git a/src/openvpn/socket.c b/src/openvpn/socket.c
index b548ab7a..e8f790ea 100644
--- a/src/openvpn/socket.c
+++ b/src/openvpn/socket.c
@@ -1916,6 +1916,7 @@  link_socket_init_phase1(struct link_socket *sock,
                         struct link_socket_addr *lsa,
                         const char *ipchange_command,
                         const struct plugin_list *plugins,
+                        const char **transport_plugin_argv,
                         int resolve_retry_seconds,
                         int mtu_discover_type,
                         int rcvbuf,
@@ -1955,6 +1956,7 @@  link_socket_init_phase1(struct link_socket *sock,
     sock->info.bind_ipv6_only = bind_ipv6_only;
     sock->info.ipchange_command = ipchange_command;
     sock->info.plugins = plugins;
+    sock->info.transport_plugin_argv = transport_plugin_argv;
     sock->server_poll_timeout = server_poll_timeout;
 
     sock->mode = mode;
diff --git a/src/openvpn/socket.h b/src/openvpn/socket.h
index 73a4ab6f..eb0b2a73 100644
--- a/src/openvpn/socket.h
+++ b/src/openvpn/socket.h
@@ -327,6 +327,7 @@  link_socket_init_phase1(struct link_socket *sock,
                         struct link_socket_addr *lsa,
                         const char *ipchange_command,
                         const struct plugin_list *plugins,
+                        const char **transport_plugin_argv,
                         int resolve_retry_seconds,
                         int mtu_discover_type,
                         int rcvbuf,