If the connection to the bus is lost while a method call is ongoing,
the method call does not get cancelled. Instead it just sits around
until it times out.
This is visible here on XO laptops when stopping the display manager
during shutdown. imsettings starts sending a sync message to give up
its bus name (via g_bus_unown_name()), then systemd terminates the
session bus at approximately the same time. imsettings then hangs for
about 20 seconds before timing out the message.
http://lists.freedesktop.org/archives/dbus/2011-September/014717.html
imsettings behaviour could be improved as described in that thread,
but I think this is a glib bug. I've also come up with the attached
patch which fixes it.
Credits for the bug-fix goes to Daniel Drake <dsd@laptop.org>. The test
case was written by David Zeuthen <zeuthen@gmail.com>.
https://bugzilla.gnome.org/show_bug.cgi?id=660637
Signed-off-by: David Zeuthen <davidz@redhat.com>
Add g_main_context_ref_thread_default(), which always returns a
reffed GMainContext, rather than sometimes returning a (non-reffed)
GMainContext, and sometimes returning NULL. This simplifies the
bookkeeping in any code that needs to keep a reference to the
thread-default context for a while.
https://bugzilla.gnome.org/show_bug.cgi?id=660994
We can't safely close the output part of the I/O stream until any
pending write or flush has been completed. In the worst case, this could
lead to an assertion failure in the worker (when the close wins the
race) or not closing the stream at all (when the write wins the race).
Bug: https://bugzilla.gnome.org/show_bug.cgi?id=651268
Bug-NB: NB#271520
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Signed-off-by: David Zeuthen <davidz@redhat.com>
Also add convenience _with_unix_fd_list variants to GDBusConnection,
GDBusProxy and GDBusMethodInvocation types to easily support this.
Signed-off-by: David Zeuthen <davidz@redhat.com>
This function implements the following logic:
if (g_variant_is_floating (value))
g_variant_ref_sink (value);
which is used for consuming the return value of callbacks that may or
may not return floating references.
This patch also replaces a few instances of the above code with the new
function (GSettings, GDBus) and lifts a long-standing restriction on the
use of floating values as the return value for signal handlers by
improving g_value_take_variant().
https://bugzilla.gnome.org/show_bug.cgi?id=627974
To help cross compilation, don't use glib-genmarshal in our
build. This is easy now that we have g_cclosure_marshal_generic().
In gobject/, add gmarshal.[ch] to git (making the existing entry
points stubs).
In gio/, simply switch to using g_cclosure_marshal_generic().
https://bugzilla.gnome.org/show_bug.cgi?id=652168
If g_bus_get_sync() fails in authentication (because e.g. the process
uid, doesn't match the expected in EXTERNAL), a secondary call to
g_bus_get_sync() would notice we aren't initialized, and try
to initialize.
The assertion here is just wrong; we now explicitly and clearly handle
both cases where we already have an error, or we already succeeded.
https://bugzilla.gnome.org/show_bug.cgi?id=635694
If specified, the signal subscription is setup client-side but the match
rule is not sent to the server. This allows the caller to manually
register more detailed match rules.
It doesn't really work right now because of a dbus-daemon(1) bug - see
the comment added in the TODO section of gdbusconnection.c. So revert
to old behavior. The downside is a lot of files in /tmp but right now
that's better than not being able to run tests in a loop.
Signed-off-by: David Zeuthen <davidz@redhat.com>
Without this fix, the ./gdbus-connection test case occasionally fails, see
https://bugzilla.gnome.org/show_bug.cgi?id=629945#c5
like this
/gdbus/connection/basic: OK
/gdbus/connection/life-cycle: **
ERROR:gdbus-connection.c:223:test_connection_life_cycle: assertion failed:
(!quit_mainloop_fired)
cleaning up bus with pid 21794
Aborted (core dumped)
because the callback didn't happen on the same thread as where we are
running the loop.
Signed-off-by: David Zeuthen <davidz@redhat.com>
Turns out that GDBusWorker will issue callbacks (in its own thread)
even after g_dbus_worker_stop() has been called. This would rarely
happen (and unreffing a connection is even rarer) so only saw this bug
occasionally when running the gdbus-connection test case in a loop.
Fix up this issue by maintaining a set of GDBusConnection objects that
are currently "alive" and do nothing in the callbacks if the passed
user_data pointer is not in this set.
Also attempted to fix up a race condition with
_g_object_wait_for_single_ref_do() and its use of GObject toggle
references - for now, just resort to busy waiting, thereby
sidestepping the toggle reference mess altogether.
Signed-off-by: David Zeuthen <davidz@redhat.com>
==7269== 144 bytes in 6 blocks are definitely lost in loss record 1,282 of 1,325
==7269== at 0x4005BDC: malloc (vg_replace_malloc.c:195)
==7269== by 0x4056B74: g_malloc (gmem.c:164)
==7269== by 0x406EDB6: g_slice_alloc (gslice.c:842)
==7269== by 0x406EDFB: g_slice_alloc0 (gslice.c:854)
==7269== by 0x413C627: g_type_create_instance (gtype.c:1867)
==7269== by 0x412276A: g_object_constructor (gobject.c:1480)
==7269== by 0x4121E5D: g_object_newv (gobject.c:1264)
==7269== by 0x4121BD3: g_object_new (gobject.c:1176)
==7269== by 0x417CFB9: g_credentials_new (gcredentials.c:156)
==7269== by 0x41D9DBC: g_unix_credentials_message_deserialize (gunixcredentialsmessage.c:149)
==7269== by 0x41C422C: g_socket_control_message_deserialize (gsocketcontrolmessage.c:198)
==7269== by 0x41BFCE3: g_socket_receive_message (gsocket.c:3289)
==7269== by 0x41D99CE: g_unix_connection_receive_credentials (gunixconnection.c:476)
==7269== by 0x41FA829: _g_dbus_auth_run_server (gdbusauth.c:987)
==7269== by 0x4205DDB: initable_init (gdbusconnection.c:2196)
Bug #629689.
Rework filter functions as per
https://bugzilla.gnome.org/show_bug.cgi?id=624546#c8
This commit breaks ABI. However, this ABI break affects only
applications using filter functions. The only known user of is dconf.
Signed-off-by: David Zeuthen <davidz@redhat.com>
Don't leak the ptr arrays in the map_sender_unique_name_to_signal_data_array
hash table.
==23440== 84 (20 direct, 64 indirect) bytes in 1 blocks are definitely lost in loss record 920 of 993
==23440== at 0x4005BDC: malloc (vg_replace_malloc.c:195)
==23440== by 0x4057094: g_malloc (gmem.c:134)
==23440== by 0x406F2D6: g_slice_alloc (gslice.c:836)
==23440== by 0x401D2D0: g_ptr_array_sized_new (garray.c:799)
==23440== by 0x401D2AC: g_ptr_array_new (garray.c:783)
==23440== by 0x420834A: g_dbus_connection_signal_subscribe (gdbusconnection.c:3084)
Bug #628436.
==31063== 98 (24 direct, 74 indirect) bytes in 1 blocks are definitely lost in loss record 946 of 1,136
==31063== at 0x4005BDC: malloc (vg_replace_malloc.c:195)
==31063== by 0x4057094: g_malloc (gmem.c:134)
==31063== by 0x406F2D6: g_slice_alloc (gslice.c:836)
==31063== by 0x4092383: g_variant_get_child_value (gvariant-core.c:847)
==31063== by 0x408BE9E: g_variant_get_variant (gvariant.c:709)
==31063== by 0x40903F5: g_variant_valist_get_nnp (gvariant.c:3767)
==31063== by 0x40907A9: g_variant_valist_get_leaf (gvariant.c:3884)
==31063== by 0x4090D10: g_variant_valist_get (gvariant.c:4065)
==31063== by 0x4090E59: g_variant_valist_get (gvariant.c:4100)
==31063== by 0x40911B6: g_variant_get_va (gvariant.c:4296)
==31063== by 0x40910BC: g_variant_get (gvariant.c:4248)
==31063== by 0x4208DAF: invoke_set_property_in_idle_cb (gdbusconnection.c:3676)
Bug #628346.
Turns out we are leaking non-floating GVariant instances returned by
get_property() functions.
Also avoid imprecise language such as "newly-allocated GVariant" as
this doesn't specify whether the variant can be floating or not.
Also see https://bugzilla.gnome.org/show_bug.cgi?id=627974 as it is
very related to this change.
Signed-off-by: David Zeuthen <davidz@redhat.com>
... that is, make it private. This makes sense because users are never
expected to create such objects themselves - only the GDBus core will
need this.
Signed-off-by: David Zeuthen <davidz@redhat.com>
Allow modifying a GDBusMessage in a filter function and also add tests
for this. This breaks API but leaves ABI (almost) intact - at least
dconf's GSettings backend (the only big user I know of) will keep
working.
https://bugzilla.gnome.org/show_bug.cgi?id=624546
Signed-off-by: David Zeuthen <davidz@redhat.com>
This prints all GDBusMethodInvocation API usage and is normally used
with the `incoming' option. Example:
# G_DBUS_DEBUG=incoming,return ./polkitd --replace
Entering main event loop
Connected to the system bus
Registering null backend at priority -10
[...]
Acquired the name org.freedesktop.PolicyKit1
[...]
========================================================================
GDBus-debug:Incoming:
<<<< METHOD INVOCATION org.freedesktop.PolicyKit1.Authority.RegisterAuthenticationAgent()
on object /org/freedesktop/PolicyKit1/Authority
invoked by name :1.26
serial 299
========================================================================
GDBus-debug:Return:
>>>> METHOD ERROR org.freedesktop.PolicyKit1.Error.Failed
message `Cannot determine session the caller is in'
in response to org.freedesktop.PolicyKit1.Authority.RegisterAuthenticationAgent()
on object /org/freedesktop/PolicyKit1/Authority
to name :1.26
reply-serial 299
[...]
========================================================================
GDBus-debug:Incoming:
<<<< METHOD INVOCATION org.freedesktop.PolicyKit1.Authority.RegisterAuthenticationAgent()
on object /org/freedesktop/PolicyKit1/Authority
invoked by name :1.2402
serial 25
========================================================================
GDBus-debug:Return:
>>>> METHOD RETURN
in response to org.freedesktop.PolicyKit1.Authority.RegisterAuthenticationAgent()
on object /org/freedesktop/PolicyKit1/Authority
to name :1.2402
reply-serial 25
Signed-off-by: David Zeuthen <davidz@redhat.com>
The D-Bus spec mentions exactly what header fields are required for
various message types. Add tests for this as well.
Also disallow empty interfaces for signals since the D-Bus spec says
this is Verboten already.
Signed-off-by: David Zeuthen <davidz@redhat.com>
Spell out "RECEIVED SIGNAL" instead of "SIGNAL" to emphasize this is
about receiving a signal, not emitting one (which is "SIGNAL
EMISSION"). Also make the "arrows" point in the "right" direction
("<<<<" vs ">>>>") - like this:
========================================================================
GDBus-debug:Signal:
<<<< RECEIVED SIGNAL org.freedesktop.DBus.NameOwnerChanged
on object /org/freedesktop/DBus
sent by name org.freedesktop.DBus
and
========================================================================
GDBus-debug:Incoming:
<<<< METHOD INVOCATION org.freedesktop.PolicyKit1.Authority.EnumerateTemporaryAuthorizations()
on object /org/freedesktop/PolicyKit1/Authority
invoked by name :1.2176
Signed-off-by: David Zeuthen <davidz@redhat.com>
This should make things easier to debug:
g_dbus_connection_real_closed: Remote peer vanished with error:
Underlying GIOStream returned 0 bytes on an async read
(g-io-error-quark, 0). Exiting.
Signed-off-by: David Zeuthen <davidz@redhat.com>
Don't do too much work in the finalizer - in particular, there's no
need to send RemoveMatch() messages to the bus daemon since we're
going to sever the connection and the bus will garbage collect
anyway. In this case it crashed the process.
Also add a test case that checks that the appropriate GDestroyNotify
callbacks are called when unreffing a connection with either 1)
exported objects; 2) signal subscriptions or 3) filter functions
.. yes, ideally apps would unregister such callbacks before giving up
their ref but that's not how things work :-)
Signed-off-by: David Zeuthen <davidz@redhat.com>
This is preferable to the current magical solution whereby the serial
is only rewritten if non-zero. In particular, it makes it easier to
send the same message on multiple connections without having to reset
the serial number.
Signed-off-by: David Zeuthen <davidz@redhat.com>
This is currently unused but might be useful in the future. For
example, it might be nice with a way to bypass the current queue of
outgoing messages - having a flag enumeration allows us to add a
G_DBUS_SEND_MESSAGE_FLAGS_BYPASS_QUEUE etc. etc.
This commit breaks ABI and API. Users of the (rarely used) API to send
messages will have to port to this new API.
Signed-off-by: David Zeuthen <davidz@redhat.com>
This is currently unused but will probably be useful in the
future. For example, we could have a _ARG0_IS_PATH to specify that
arg0 should be used for arg0path.
This commit breaks API and ABI. Users of
g_dbus_connection_signal_subscribe() will need to port to this new
version.
Signed-off-by: David Zeuthen <davidz@redhat.com>
If the subtree introspection function indicates that an interface exists
but then the dispatch function returns a NULL vtable for that interface,
issue a g_warning pointing programmers in the right direction.
Return a NULL terminated C array instead of a GPtrArray
Also, document that %NULL is a permitted return value and clarify its
meaning.
Finally, avoid calling the enumeration function during dispatch when the
G_DBUS_SUBTREE_FLAGS_DISPATCH_TO_UNENUMERATED_NODES flag was given.
... so it is async, cancelable and returns an error. Also provide a
synchronous version.
This is an API/ABI break but it is expected that only very few
applications use this API.
Signed-off-by: David Zeuthen <davidz@redhat.com>
E.g. move these C structures out of public header files and into their
respective C files. Also nuke padding since this is no longer needed.
This leaves only GDBusProxy as an extendable type.
Signed-off-by: David Zeuthen <davidz@redhat.com>
While this a dangerous thing to allow (collissions, reply_serial not
matching up etc.), the added flexibility makes this a good trade-off -
for example, with this feature, it's now a lot easier to build message
routers.
Signed-off-by: David Zeuthen <davidz@redhat.com>
Also add a 'address' G_DBUS_DEBUG option that will print out useful
debug information such as
GDBus-debug:Address: In g_dbus_address_get_for_bus_sync() for bus type `session'
GDBus-debug:Address: env var DBUS_SESSION_BUS_ADDRESS is not set
GDBus-debug:Address: env var DBUS_SYSTEM_BUS_ADDRESS is not set
GDBus-debug:Address: env var DBUS_STARTER_BUS_TYPE is not set
GDBus-debug:Address: Running `dbus-launch --autolaunch=05e508961149264c9b750a4c494aa6f7 --binary-syntax --close-stderr' to get bus address (possibly autolaunching)
GDBus-debug:Address: dbus-launch output:
0000: 75 6e 69 78 3a 61 62 73 74 72 61 63 74 3d 2f 74 unix:abstract=/t
0010: 6d 70 2f 64 62 75 73 2d 77 42 41 6f 4b 59 49 52 mp/dbus-wBAoKYIR
0020: 7a 75 2c 67 75 69 64 3d 30 34 30 64 31 33 66 33 zu,guid=040d13f3
0030: 30 61 30 62 35 32 63 32 30 66 36 32 63 34 31 63 0a0b52c20f62c41c
0040: 30 30 30 30 35 30 38 64 00 d2 38 00 00 01 00 40 0000508d..8....@
0050: 05 00 00 00 00 .....
GDBus-debug:Address: dbus-launch stderr output:
14542: Autolaunch enabled (using X11).
14542: --exit-with-session automatically enabled
14542: Connected to X11 display ':0.0'
14542: === Parent dbus-launch continues
14542: Waiting for babysitter's intermediate parent
14542: Reading address from bus
14542: Reading PID from daemon
14542: Saving x11 address
14542: Created window 88080385
14542: session file: /root/.dbus/session-bus/05e508961149264c9b750a4c494aa6f7-0
14542: dbus-launch exiting
GDBus-debug:Address: Returning address `unix:abstract=/tmp/dbus-wBAoKYIRzu,guid=040d13f30a0b52c20f62c41c0000508d' for bus type `session'
and
GDBus-debug:Address: In g_dbus_address_get_for_bus_sync() for bus type `session'
GDBus-debug:Address: env var DBUS_SESSION_BUS_ADDRESS is not set
GDBus-debug:Address: env var DBUS_SYSTEM_BUS_ADDRESS is not set
GDBus-debug:Address: env var DBUS_STARTER_BUS_TYPE is not set
GDBus-debug:Address: Running `dbus-launch --autolaunch=05e508961149264c9b750a4c494aa6f7 --binary-syntax --close-stderr' to get bus address (possibly autolaunching)
GDBus-debug:Address: dbus-launch output:
0000: 75 6e 69 78 3a 61 62 73 74 72 61 63 74 3d 2f 74 unix:abstract=/t
0010: 6d 70 2f 64 62 75 73 2d 77 42 41 6f 4b 59 49 52 mp/dbus-wBAoKYIR
0020: 7a 75 2c 67 75 69 64 3d 30 34 30 64 31 33 66 33 zu,guid=040d13f3
0030: 30 61 30 62 35 32 63 32 30 66 36 32 63 34 31 63 0a0b52c20f62c41c
0040: 30 30 30 30 35 30 38 64 00 d2 38 00 00 01 00 40 0000508d..8....@
0050: 05 00 00 00 00 .....
GDBus-debug:Address: dbus-launch stderr output:
14549: Autolaunch enabled (using X11).
14549: --exit-with-session automatically enabled
14549: Connected to X11 display ':0.0'
14549: dbus-daemon is already running. Returning existing parameters.
14549: dbus-launch exiting
GDBus-debug:Address: Returning address `unix:abstract=/tmp/dbus-wBAoKYIRzu,guid=040d13f30a0b52c20f62c41c0000508d' for bus type `session'
Note that things work exactly like libdbus, e.g. from the
dbus-launch(1) man page:
Whenever an autolaunch occurs, the application that had to start a
new bus will be in its own little world; it can effectively end up
starting a whole new session if it tries to use a lot of bus
services. This can be suboptimal or even totally broken, depending
on the app and what it tries to do.
[...]
You can always avoid autolaunch by manually setting
DBUS_SESSION_BUS_ADDRESS. Autolaunch happens because the default
address if none is set is "autolaunch:", so if any other address is
set there will be no autolaunch. You can however include autolaunch
in an explicit session bus address as a fallback, for example
DBUS_SESSION_BUS_ADDRESS="something:,autolaunch:" - in that case if
the first address doesn't work, processes will autolaunch. (The bus
address variable contains a comma-separated list of addresses to
try.)
Signed-off-by: David Zeuthen <davidz@redhat.com>
This commit adds the following G_DBUS_DEBUG flags
- emission
- incoming
- call
- signal
- payload
https://bugzilla.gnome.org/show_bug.cgi?id=620913
Signed-off-by: David Zeuthen <davidz@redhat.com>
Things will still work fine if the GDBusInterfaceInfo is allocated
statically because if so the ref_count will be -1.
Signed-off-by: David Zeuthen <davidz@redhat.com>
Without this guarantee, peer-to-peer connections are not very
useful. However, with this guarantee it's possible to export objects
in a handler for the GDBusServer::new-connection signal.
There are two caveats with this patch
- it won't work on message bus connections
- we don't queue up messages to be written
that can be addresses later if needed.
https://bugzilla.gnome.org/show_bug.cgi?id=623142
Signed-off-by: David Zeuthen <davidz@redhat.com>
There's a couple of places in GDBus where it's a programming error
(e.g. we'll assert or spew via e.g. g_warning()) to use the API on a
closed connection. This approach can never work since a
GDBusConnection can be closed at any point in time outside of
programmer control.
Just change the code to return a run-time error (e.g. return
G_IO_ERROR_CLOSED when sending messages, invoking methods) or silently
accept the request (e.g. exporting objects, registering for signals)
without doing anything.
Note that a GDBusConnection object is always useless after being
closed - e.g. there's no way to "reopen" a connection - the user will
have to create a new object and use that instead.
https://bugzilla.gnome.org/show_bug.cgi?id=623143
Signed-off-by: David Zeuthen <davidz@redhat.com>
This patch breaks some rarely-used public API (only known user is
dconf).
This patch is based on work from Peng Huang <shawn.p.huang@gmail.com>.
See https://bugzilla.gnome.org/show_bug.cgi?id=621945
Signed-off-by: David Zeuthen <davidz@redhat.com>
Allow constructing a GDBusProxy for well-known names as discussed here
http://mail.gnome.org/archives/gtk-devel-list/2009-October/msg00075.html
including test cases.
Make it possible to create a GDBusProxy for a GBusType instead of a
GDBusConnection. This requires G_BUS_TYPE_NONE so add that too.
Nuke g_bus_watch_proxy() since one can now more or less use GDBusProxy
for this.
Port gdbus-example-watch-proxy to this new API and include this
example in the GDBusProxy doc page.
Also nuke the GType parameter from the GDBusProxy constructors as
requested here: https://bugzilla.gnome.org/show_bug.cgi?id=621229
Also update the porting guide and other API docs for this change.
Also fix a bug in the signal dispatching code so each subscriber only
get notified once, not N times, for the same signal. Also add a test
case for this.
https://bugzilla.gnome.org/show_bug.cgi?id=621213
Signed-off-by: David Zeuthen <davidz@redhat.com>
There was a slight race where we ended up calling into user code if
the user managed to unregister an object (or subtree) in the window
between
- processing the remote call on the worker thread; and
- continuing handling it on the user code thread (via an idle handler)
This patch fixes the problem.
Signed-off-by: David Zeuthen <davidz@redhat.com>
This allows the caller to specify the reply type that they are expecting
for this call. If the reply comes back with the wrong type, GDBus will
generate an appropriate error internally.
- add a GVariantType * argument to g_dbus_connection_call() and
_call_sync().
- move the internal API for computing message types from introspection
data to be based on GVariantType instead of strings. Update users
of this code.
- have GDBusProxy pass this calculated GVariantType into
g_dbus_connection_call(). Remove the checks done in GDBusProxy.
- Update other users of the code (test cases, gdbus-tool, GSettings
tool, etc). In some cases, remove redundant checks; in some other
cases, we are fixing bugs because no checking was done where it
should have been.
Closes bug #619391.
Ryan pointed out on IRC that we didn't do anything here. Looking at
the code, it's painfully obvious that we should be returning an error
here since a comment already says that we've exhausted all possible
options.
Signed-off-by: David Zeuthen <davidz@redhat.com>
- Fix various #include issues
- Change #error to #warning for the EXTERNAL authentication mechanism.
It is not clear if this should work on Win32 at all.
- Call close() before unlink() for the SHA1 keyring
- Change #error to #warning so we don't forget to do
permission checking of the .dbus-keyrings directory
- Use Win32 SID for the SHA1 auth mech
- Apparently we can't use word 'interface' as an identifier
- Implement a _g_dbus_win32_get_user_sid() function. For now it's
private. Don't know if it should be public somewhere. Maybe in
a future GCredentials support for Win32? I don't know.
- GFileDescriptorBased is not available on Win32. So avoid using
it in GLocalFile stuff. Now, Win32 still uses GLocalFile + friends
(which works with file descriptors) so expose a private function
to get the fd for an OutputStream so things still work.
- Fixup gio.symbols
- Fixup tests/gdbus-peer.c so it builds
With this, at least things compile and the gdbus-peer.exe test case
passes. Which is a great start. I've tested this by cross-compiling on
a x86_64 Fedora 13 host using mingw32 and running the code on a 32-bit
Windows 7 box.
https://bugzilla.gnome.org/show_bug.cgi?id=619142
Signed-off-by: David Zeuthen <davidz@redhat.com>
Without this fix, we segfault if the exported object returned an error
on all get_property() calls (in reality, this never happens).
Signed-off-by: David Zeuthen <davidz@redhat.com>
Free the bus address after creating the singleton.
==26308== 39,736 (10,517 direct, 29,219 indirect) bytes in 388 blocks
are definitely lost in loss record 14 of 15
==26308== at 0x4024D2E: malloc (vg_replace_malloc.c:207)
==26308== by 0x4079A90: g_malloc (gmem.c:135)
==26308== by 0x4079DC8: g_malloc_n (gmem.c:252)
==26308== by 0x4095607: g_strdup (gstrfuncs.c:102)
==26308== by 0x4216B9A: g_dbus_address_get_for_bus_sync
(gdbusaddress.c:961)
==26308== by 0x422A7AE: get_uninitialized_connection
(gdbusconnection.c:5241)
Bug #618622.
This is to match g_dbus_connection_new(). This extension allows us to
extend GDBusAuthObserver to also be used in client-side authentication
in the future (right now it's only used on the server-side).
This is needed to e.g. allow encoding maybe types (once we add
G_DBUS_CAPABILITY_FLAGS_MAYBE_TYPES) if, and only if, that capability
has been negotiated with the peer (via authentication).
