stream: Add basic stream service for systemd sockets

This allows systemd socket activation by passing URIs such as systemd://foo
to plugins such as VICI.

For example setting charon.plugins.vici.socket = systemd://vici, a
systemd socket file descriptor with the name "vici" will be picked up.

So these would be the corresponding unit options:

  [Socket]
  FileDescriptorName=vici
  Service=strongswan.service

  ListenStream=/run/charon.vici

The implementation currently is very basic and right now only the first
file descriptor for a particular identifier is picked up if there are
multiple socket units with the same FileDescriptorName.

Signed-off-by: aszlig <[email protected]>

Closes strongswan/strongswan#79.

src/libstrongswan/networking/streams/stream_manager.c

@@ -21,6 +21,9 @@
 # include "stream_unix.h"
 # include "stream_service_unix.h"
 #endif
+#ifdef USE_SYSTEMD
+# include "stream_service_systemd.h"
+#endif
 
 #include <threading/rwlock.h>
 
@@ -241,6 +244,9 @@ stream_manager_t *stream_manager_create()
 	add_stream(this, "unix://", stream_create_unix);
 	add_service(this, "unix://", stream_service_create_unix);
 #endif
+#ifdef USE_SYSTEMD
+	add_service(this, "systemd://", stream_service_create_systemd);
+#endif
 
 	return &this->public;
 }