bus-util: add helper for getting PidRef structs from bus

This adds two helpers: one for extracting a PidRef from an sd_bus_creds
object, and one from doing this from and sd_bus_message object.

src/shared/bus-util.c

@@ -710,3 +710,47 @@ int bus_property_get_string_set(
 
         return bus_message_append_string_set(reply, *s);
 }
+
+int bus_creds_get_pidref(
+                sd_bus_creds *c,
+                PidRef *ret) {
+
+        int pidfd = -EBADF;
+        pid_t pid;
+        int r;
+
+        assert(c);
+        assert(ret);
+
+        r = sd_bus_creds_get_pid(c, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_creds_get_pidfd_dup(c, &pidfd);
+        if (r < 0 && r != -ENODATA)
+                return r;
+
+        *ret = (PidRef) {
+                .pid = pid,
+                .fd = pidfd,
+        };
+
+        return 0;
+}
+
+int bus_query_sender_pidref(
+                sd_bus_message *m,
+                PidRef *ret) {
+
+        _cleanup_(sd_bus_creds_unrefp) sd_bus_creds *creds = NULL;
+        int r;
+
+        assert(m);
+        assert(ret);
+
+        r = sd_bus_query_sender_creds(m, SD_BUS_CREDS_PID|SD_BUS_CREDS_PIDFD, &creds);
+        if (r < 0)
+                return r;
+
+        return bus_creds_get_pidref(creds, ret);
+}

src/shared/bus-util.h

@@ -11,6 +11,7 @@
 
 #include "errno-util.h"
 #include "macro.h"
+#include "pidref.h"
 #include "runtime-scope.h"
 #include "set.h"
 #include "string-util.h"
@@ -73,3 +74,6 @@ extern const struct hash_ops bus_message_hash_ops;
 int bus_message_append_string_set(sd_bus_message *m, Set *s);
 
 int bus_property_get_string_set(sd_bus *bus, const char *path, const char *interface, const char *property, sd_bus_message *reply, void *userdata, sd_bus_error *error);
+
+int bus_creds_get_pidref(sd_bus_creds *c, PidRef *ret);
+int bus_query_sender_pidref(sd_bus_message *m, PidRef *ret);