Fix string leaks in deserialize vfuncs

Fix string leaks in deserialize vfuncs

When an object contains char * properties, its deserialize function will
overwrite these string values without freeing them first. They are not
necessarily NULL as they can have (default) values set upon construction,
so they need to be g_free'd before being overwritten.

For example, IBusEngineDesc::longname, IBusEngineDesc::description,
IBusEngineDesc::language, ... are all set to "" upon construction (instead of
NULL), so the corresponding IBusEngineDesc fields must be freed before
being overwritten during deserialization.

This commit introduces a ibus_g_variant_get_child_string() to do this
and set the string value.

This leak was reported by valgrind:

==22163== 59 bytes in 59 blocks are definitely lost in loss record 1,633 of 2,720
==22163==    at 0x4A0645D: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==22163==    by 0x56DFDF2: g_malloc (gmem.c:97)
==22163==    by 0x56E011D: g_malloc_n (gmem.c:338)
==22163==    by 0x56FAFCC: g_strdup (gstrfuncs.c:356)
==22163==    by 0x546CDB8: g_value_dup_string (gvaluetypes.c:1136)
==22163==    by 0x4E43A98: ibus_engine_desc_set_property (ibusenginedesc.c:385)
==22163==    by 0x5446CA3: object_set_property (gobject.c:1378)
==22163==    by 0x54484BB: g_object_constructor (gobject.c:2020)
==22163==    by 0x4E24564: ibus_object_constructor (ibusobject.c:111)
==22163==    by 0x5447577: g_object_new_with_custom_constructor (gobject.c:1645)
==22163==    by 0x5447787: g_object_new_internal (gobject.c:1722)
==22163==    by 0x5447C75: g_object_newv (gobject.c:1868)
==22163==    by 0x544737A: g_object_new (gobject.c:1568)
==22163==    by 0x4E2521C: ibus_serializable_deserialize (ibusserializable.c:292)
==22163==    by 0x4E480E0: ibus_component_deserialize (ibuscomponent.c:408)
==22163==    by 0x4E2523E: ibus_serializable_deserialize (ibusserializable.c:294)
==22163==    by 0x4E4C1D1: ibus_registry_deserialize (ibusregistry.c:202)
==22163==    by 0x4E4C95C: ibus_registry_load_cache_file (ibusregistry.c:362)
==22163==    by 0x4E4C6A4: ibus_registry_load_cache (ibusregistry.c:302)
==22163==    by 0x40EBCD: bus_ibus_impl_registry_init (ibusimpl.c:1871)
==22163==    by 0x40C1D4: bus_ibus_impl_init (ibusimpl.c:424)
==22163==    by 0x5460FCD: g_type_create_instance (gtype.c:1868)
==22163==    by 0x5448466: g_object_constructor (gobject.c:2006)
==22163==    by 0x4E24564: ibus_object_constructor (ibusobject.c:111)
==22163==    by 0x5447577: g_object_new_with_custom_constructor (gobject.c:1645)
==22163==    by 0x5447787: g_object_new_internal (gobject.c:1722)
==22163==    by 0x54483C1: g_object_new_valist (gobject.c:1980)
==22163==    by 0x54473C9: g_object_new (gobject.c:1571)
==22163==    by 0x40E94A: bus_ibus_impl_get_default (ibusimpl.c:1807)
==22163==    by 0x41D880: bus_server_init (server.c:100)
==22163==    by 0x420E91: main (main.c:236)

BUG=http://code.google.com/p/ibus/issues/detail?id=1712

[Peng, 2014-06-05 14:39:06]

lgtm with nits

https://codereview.appspot.com/104850043/diff/1/src/ibuscomponent.c
File src/ibuscomponent.c (right):

https://codereview.appspot.com/104850043/diff/1/src/ibuscomponent.c#newcode395
src/ibuscomponent.c:395: ibus_g_variant_get_child_string (variant, retval++,
&component->priv->textdomain);
Some lines are more than 80 chars. And other places.

[teuf, 2014-06-05 21:26:34]

https://codereview.appspot.com/104850043/diff/1/src/ibuscomponent.c
File src/ibuscomponent.c (right):

https://codereview.appspot.com/104850043/diff/1/src/ibuscomponent.c#newcode395
src/ibuscomponent.c:395: ibus_g_variant_get_child_string (variant, retval++,
&component->priv->textdomain);
On 2014/06/05 14:39:06, Peng wrote:
> Some lines are more than 80 chars. And other places.

I've fixed that locally, but I don't know how to attach an updated patch here :(
Should I attach that to the ticket I opened on google code ?

[fujiwara, 2014-06-06 07:16:27]

https://codereview.appspot.com/104850043/diff/1/src/ibuscomponent.c
File src/ibuscomponent.c (right):

https://codereview.appspot.com/104850043/diff/1/src/ibuscomponent.c#newcode395
src/ibuscomponent.c:395: ibus_g_variant_get_child_string (variant, retval++,
&component->priv->textdomain);
On 2014/06/05 21:26:34, teuf wrote:
> On 2014/06/05 14:39:06, Peng wrote:
> > Some lines are more than 80 chars. And other places.
> 
> I've fixed that locally, but I don't know how to attach an updated patch here
:(
> Should I attach that to the ticket I opened on google code ?

I integrated your patch.
If you will file another patch, you could use git-cl directly.
The usage of git-cl is described in the commit log:

% cd ibus
% git log codereview.settings