sd-bus: introduce API for re-enqueuing incoming messages

When authorizing via PolicyKit we want to process incoming method calls
twice: once to process and figure out that we need PK authentication,
and a second time after we aquired PK authentication to actually execute
the operation. With this new call sd_bus_enqueue_for_read() we have a
way to put an incoming message back into the read queue for this
purpose.

This might have other uses too, for example debugging.

(cherry picked from commit 1068447e6954dc6ce52f099ed174c442cb89ed54)

zjs: patch modified to not make the function public
(cherry picked from commit 83bfc0d8dd026814d23e3fdfa46806394f775526)

2 files changed, 25 insertions, 0 deletions

diff --git a/src/libsystemd/sd-bus/bus-message.h b/src/libsystemd/sd-bus/bus-message.h
index ced0bb3d34..fa17856444 100644
--- a/src/libsystemd/sd-bus/bus-message.h
+++ b/src/libsystemd/sd-bus/bus-message.h
@@ -225,3 +225,4 @@ void bus_message_set_sender_local(sd_bus *bus, sd_bus_message *m);
 
 sd_bus_message* bus_message_ref_queued(sd_bus_message *m, sd_bus *bus);
 sd_bus_message* bus_message_unref_queued(sd_bus_message *m, sd_bus *bus);
+int sd_bus_enqeue_for_read(sd_bus *bus, sd_bus_message *m);
diff --git a/src/libsystemd/sd-bus/sd-bus.c b/src/libsystemd/sd-bus/sd-bus.c
index 026ac8cb94..df9eadc849 100644
--- a/src/libsystemd/sd-bus/sd-bus.c
+++ b/src/libsystemd/sd-bus/sd-bus.c
@@ -4194,3 +4194,27 @@ _public_ int sd_bus_get_close_on_exit(sd_bus *bus) {
 
         return bus->close_on_exit;
 }
+
+int sd_bus_enqeue_for_read(sd_bus *bus, sd_bus_message *m) {
+        int r;
+
+        assert_return(bus, -EINVAL);
+        assert_return(bus = bus_resolve(bus), -ENOPKG);
+        assert_return(m, -EINVAL);
+        assert_return(m->sealed, -EINVAL);
+        assert_return(!bus_pid_changed(bus), -ECHILD);
+
+        if (!BUS_IS_OPEN(bus->state))
+                return -ENOTCONN;
+
+        /* Re-enqeue a message for reading. This is primarily useful for PolicyKit-style authentication,
+         * where we want accept a message, then determine we need to interactively authenticate the user, and
+         * when we have that process the message again. */
+
+        r = bus_rqueue_make_room(bus);
+        if (r < 0)
+                return r;
+
+        bus->rqueue[bus->rqueue_size++] = bus_message_ref_queued(m, bus);
+        return 0;
+}