Consider the following code:

#include <dbus/dbus.h>

#include <assert.h>

int
main (int   argc,
      char *arvgv[])
{
	DBusMessage *   method_call;
	DBusMessageIter iter;
	DBusMessageIter array_iter;
	DBusMessageIter struct_iter;
	const char *    str_value;

	method_call = dbus_message_new_method_call ("com.netsplit.Nih",
						    "/com/netsplit/Nih",
						    "com.netsplit.Nih.Test",
						    "Test");
	assert (method_call);

	dbus_message_iter_init_append (method_call, &iter);

	assert (dbus_message_iter_open_container (&iter, DBUS_TYPE_ARRAY,
						  (DBUS_STRUCT_BEGIN_CHAR_AS_STRING
						   DBUS_TYPE_STRING_AS_STRING
						   DBUS_TYPE_STRING_AS_STRING
						   DBUS_STRUCT_END_CHAR_AS_STRING),
						  &array_iter));

	assert (dbus_message_iter_open_container (&array_iter, DBUS_TYPE_STRUCT,
						  NULL,
						  &struct_iter));

	str_value = "peaches";
	assert (dbus_message_iter_append_basic (&struct_iter, DBUS_TYPE_STRING,
						&str_value));

	/* uh-oh, error, try and unwind */

	assert (dbus_message_iter_close_container (&array_iter, &struct_iter));
	assert (dbus_message_iter_close_container (&iter, &array_iter));
	dbus_message_unref (method_call);

	dbus_shutdown ();

	return 0;
}


The error we try and unwind from could be a bad return from dbus_message_iter_append_basic(), a bad return from dbus_message_iter_close_container() [which "hoses" the message] or an error inside the program or bindings -- either way, we need to unwind and can't carry on.

Unfortunately this isn't possible.

Closing the container will assert:

process 28130: Array or variant type requires that type string be written, but end_struct was written.
The overall signature expected here was 'a(ss)' and we are on byte 3 of that signature.
File "dbus-marshal-recursive.c" line 1726 process 28130 should not have been reached: bad type inserted somewhere inside an array or variant
  /lib/libdbus-1.so.3 [0x7fd078c32e62]
  /lib/libdbus-1.so.3 [0x7fd078c2d649]
  /lib/libdbus-1.so.3 [0x7fd078c1a330]
  /lib/libdbus-1.so.3 [0x7fd078bf2d39]
  /lib/libdbus-1.so.3 [0x7fd078bf381e]
  /lib/libdbus-1.so.3(dbus_message_iter_close_container+0x202) [0x7fd078bfb6db]
  ./leak [0x4008bc]
  /lib/libc.so.6(__libc_start_main+0xe6) [0x7fd0788795a6]
  ./leak [0x4006d9]
zsh: abort (core dumped)  ./leak

Not closing the container will leak memory:

==10711== 13 bytes in 1 blocks are indirectly lost in loss record 1 of 2
==10711==    at 0x4C279E1: realloc (vg_replace_malloc.c:429)
==10711==    by 0x41E2C2: dbus_realloc (dbus-memory.c:601)
==10711==    by 0x41FABE: reallocate_for_length (dbus-string.c:364)
==10711==    by 0x41FD28: set_length (dbus-string.c:404)
==10711==    by 0x422116: _dbus_string_lengthen (dbus-string.c:872)
==10711==    by 0x422985: _dbus_string_alloc_space (dbus-string.c:1005)
==10711==    by 0x44613B: writer_recurse_array (dbus-marshal-recursive.c:1847)
==10711==    by 0x4467A1: _dbus_type_writer_recurse_contained_len (dbus-marshal-recursive.c:2066)
==10711==    by 0x44684A: _dbus_type_writer_recurse (dbus-marshal-recursive.c:2106)
==10711==    by 0x40840D: dbus_message_iter_open_container (dbus-message.c:2402)
==10711==    by 0x403257: main (leak.c:24)
==10711== 
==10711== 
==10711== 37 (24 direct, 13 indirect) bytes in 1 blocks are definitely lost in loss record 2 of 2
==10711==    at 0x4C278AE: malloc (vg_replace_malloc.c:207)
==10711==    by 0x41E05D: dbus_malloc (dbus-memory.c:471)
==10711==    by 0x4076C9: _dbus_message_iter_open_signature (dbus-message.c:2113)
==10711==    by 0x408374: dbus_message_iter_open_container (dbus-message.c:2393)
==10711==    by 0x403257: main (leak.c:24)

This is because the contained signature of the iterator isn't attached to the message, unref'ing the message will not free it.