Hello,

I have some problems calling following C function with a string as
value:

dbus_bool_t dbus_message_iter_append_basic(DBusMessageIter *iter, int
type, const void *value)

I attached it via ffi:

attach_function(:dbus_message_iter_append_basic,
  :dbus_message_iter_append_basic, [ :pointer,
DBusType, :pointer ], :bool
)

(DBusType is an enum with the allowed types as integer.)

In C it should look like this and it allows several types casted to
void:

DBusMessageIter iter;
char *value = "foobar";

dbus_message_iter_append_basic(&iter, DBUS_TYPE_STRING, &value);

I will now post what I tried with the related error message:

1)
pname = FFI::MemoryPointer.new(:pointer)
pname.write_string("subtle")
dbus_message_iter_append_basic(piter, :type_string, pname)

Ruby exception: IndexError: Memory access offset=0 size=6 is out of
bounds

2)
pname = FFI::MemoryPointer.new(:string)
pname.write_string("subtle")
dbus_message_iter_append_basic(piter, :type_string, pname)

Ruby exception: ArgumentError: Unknown native type

3)
pname = FFI::MemoryPointer.from_string("subtle")
dbus_message_iter_append_basic(piter, :type_string, pname)

Segmentation fault: (Backtrace from valgrind)
==8501== Invalid read of size 1
==8501==    at 0x4024878: strlen (in /usr/lib/valgrind/
vgpreload_memcheck-x86-linux.so)
==8501==    by 0x5A56B8C: _dbus_marshal_write_basic (in /usr/lib/
libdbus-1.so.3.4.0)
==8501==    by 0x5A42962: _dbus_type_writer_write_basic (in /usr/lib/
libdbus-1.so.3.4.0)
==8501==    by 0x5A4789D: dbus_message_iter_append_basic (in /usr/lib/
libdbus-1.so.3.4.0)
...

4)
I attached another function and changed value type to :string:

attach_function(:dbus_message_iter_append_string,
    :dbus_message_iter_append_basic, [ :pointer,
DBusType, :string ], :bool
)

Segmentation fault again:
==8524== Invalid read of size 1
==8524==    at 0x4024878: strlen (in /usr/lib/valgrind/
vgpreload_memcheck-x86-linux.so)
==8524==    by 0x5A56B8C: _dbus_marshal_write_basic (in /usr/lib/
libdbus-1.so.3.4.0)
==8524==    by 0x5A42962: _dbus_type_writer_write_basic (in /usr/lib/
libdbus-1.so.3.4.0)
==8524==    by 0x5A4789D: dbus_message_iter_append_basic (in /usr/lib/
libdbus-1.so.3.4.0)
...

Any options left?

Thanks in advance.