sbus: Add sbus_vtable and update codegen to support it

Each interface is a vtable structure derived from
sbus_vtable, in the sense that it has an sbus_vtable
struct as its first argument. This lets us upcast the
interface vtable structure to an sbus_vtable and dispatch
to it dynamically and cleanly.

The interface metadata contains information about which
vtable offset in the interface metadata should be dispatched
to for a given function. This is a common scheme, not only
among dbus implementations, but also compiled languages.

Currently all the vtable functions are of type
sbus_msg_handler_fn. These are the handlers we are familiar
with and perform raw processing of the message. Later commits
will introduce type safe handlers that levelage compile checking
and automatic argument packing/unpacking.

Although this may seem contrived now, the remainder of the
dbus infrastructure work will build on this, including
ofd.Properties, ofd.ObjectManager, ofd.Introspect, compiler
checked type safe unpacking/packing, etc.

The codegen now generates vtable structures for each interface
along-side the metadata, and fills in vtable offsets
appropriately.

It is obviously still possible to hand-craft such vtables and
metadata if needed for a special case.

Once again examples output can be found at:

  src/tests/sbus_codegen_tests_generated.h

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
Reviewed-by: Sumit Bose <sbose@redhat.com>
Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/src/tests/sbus_codegen_tests.c b/src/tests/sbus_codegen_tests.c
index 6b2abf8bc..39856fac7 100644
--- a/src/tests/sbus_codegen_tests.c
+++ b/src/tests/sbus_codegen_tests.c
@@ -112,6 +112,38 @@ START_TEST(test_signals)
 }
 END_TEST
 
+static int
+mock_move_universe(DBusMessage *msg, struct sbus_connection *conn)
+{
+    /* not called */
+    return 0;
+}
+
+static int
+mock_crash_now(DBusMessage *msg, struct sbus_connection *conn)
+{
+    /* not called */
+    return 0;
+}
+
+START_TEST(test_vtable)
+{
+    struct com_planetexpress_Ship vtable = {
+        { &com_planetexpress_Ship_meta, 0 },
+        mock_move_universe,
+        mock_crash_now,
+    };
+
+    /*
+     * These are not silly tests:
+     * - Will fail compilation if c-symbol name was not respected
+     * - Will fail if method order was not respected
+     */
+    ck_assert(vtable.crash_now == mock_crash_now);
+    ck_assert(vtable.MoveUniverse == mock_move_universe);
+}
+END_TEST
+
 Suite *create_suite(void)
 {
     Suite *s = suite_create("sbus_codegen");
@@ -123,6 +155,7 @@ Suite *create_suite(void)
     tcase_add_test(tc, test_methods);
     tcase_add_test(tc, test_properties);
     tcase_add_test(tc, test_signals);
+    tcase_add_test(tc, test_vtable);
 
     /* Add all test cases to the test suite */
     suite_add_tcase(s, tc);