Re: 0-size array marshaling ?

Hi,
Thanks for the tip.
Answer is: always pad, even with 0-size array.
Test code in attachment.
I think I've fixed dbus-java code in https://github.com/jeanparpaillon/
dbus-java
Would be glad to push into the right repository, but freedesktop one
does not seem to be up-to-date (no 2.8 tag).
Regards
Jean
Le mardi 05 juillet 2016 à 10:41 +0100, Simon McVittie a écrit :
> On 04/07/16 14:43, Jean Parpaillon wrote:
> > The question is: for 0-size array, is padding to the alignment
> > boundary
> > of the array element type required ?
> 
> libdbus (dbus.git) is the reference implementation. What does it do?
> That's your answer. I would be happy to review a spec patch that
> clarifies what the right thing is (via
> 
> re>).
> 
> Because the array length is aligned to a 4-byte boundary, I would
> suggest serializing this message:
> 
> - type 'u', uint32 0x11223344 (to make it easy to find the payload)
> - type 'y', byte with arbitrary non-zero value, say 0x42
> - type 'at', empty array of uint64
> - type 'y', byte with arbitrary non-zero value, say 0x23
> 
> and looking at the resulting serialized bytes. If arrays of length 0
> do
> insert padding appropriate for the content, I would expect this hex-
> dump:
> 
> 44 33 22 11                 # uint32 (I've assumed little-endian)
>             42              # first byte
>                00 00 00     # pad to 4-byte boundary
> 00 00 00 00                 # array length
>             00 00 00 00     # pad to 8-byte boundary
>                             # no array contents
> 23                          # second byte
> 
> and if they don't, I would expect:
> 
> 44 33 22 11                 # uint32 (I've assumed little-endian)
>             42              # first byte
>                00 00 00     # pad to 4-byte boundary
> 00 00 00 00                 # array length
>                             # no padding, no array contents
>             23              # second byte
> 
> Whichever one libdbus does, that's correct and the other one is
> wrong.
> 
> Regards,
>     S
-- 
Jean Parpaillon
--
Open Source Consultant
Director @ OW2 Consortium
OCCIware Strategic Orientation Committee Chairman
Research Engineer @ Inria
--
Phone: +33 6 30 10 92 86
im: [email protected]
skype: jean.parpaillon
linkedin: http://www.linkedin.com/in/jeanparpaillon/en

_______________________________________________
dbus mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/dbus

#include <stdlib.h>
#include <stdio.h>

#include <dbus/dbus.h>

void main(int argc, char* argv[]) {
  DBusMessage* m;
  dbus_uint32_t arg_a = 0x11223344;
  char arg_b = 0x42;
  const dbus_uint64_t array[] = {};
  const dbus_uint64_t *arg_c = array;
  char arg_d = 0x23;

  char* wire;
  int len;

  m = dbus_message_new_method_call(NULL,
				   "/",
				   NULL,
				   "Test");
  dbus_message_append_args(m,
			   DBUS_TYPE_UINT32, &arg_a,
			   DBUS_TYPE_BYTE, &arg_b,
			   DBUS_TYPE_ARRAY, DBUS_TYPE_UINT64, &arg_c, 0,
			   DBUS_TYPE_BYTE, &arg_d,
			   DBUS_TYPE_INVALID);
  dbus_message_marshal(m, &wire, &len);

  for (int i = 0; i < len; i++) {
    printf("%02x", wire[i]);
    if ( (i+1) % 8) {
      printf(" ");
    } else {
      printf("\n");
    }
  }
  
  exit(0);
}