Re: ORBit transfer of image data - more info please

[Michael Meeks <michael ximian com>]

Hi Peter,

On Fri, 2003-04-25 at 13:23, Peter Van Osta wrote:
> I don't seem to get it right to transfer images from the server to the
> client, on the client side I ahve the following code:

	:-) cf. my comments on your bugreport.

> 	ret = Ezx_Srvr_ReadImage( server, &img, &strg, &message, &ev );

	For an inout sequence things are complicated; I think you're likely to
be on-course for much confusion if you go this way; why don't you simply
return the structure, and then free it ? I forget the exact semantics
myself. AFAIR though with an inout sequence argument you have to
allocate the _buffer; for it to free (or send a 0 length sequence in),
the ORB will free that, and replace it with the new value on return -
but as I say - it's a potentially confusing way to use the binding, and
scripting languages tend not to like out/inout arguments anyway so ...

> 	if( message )
> 		CORBA_free( message );

	It's worth noting that you have to check for an exception before using
the return value of a CORBA method; on exception the return values are
undefined (freed/uninitialized by the ORB itself); so you need:

	if (ev._major != CORBA_NO_EXCEPTION) {
		handle_error;
		return;
	}

> On the server side I just put the following code for a test, but all I
> get is a "core" dump:

	OK;

> static CORBA_short impl_Ezx_Srvr_ReadImage(impl_POA_Ezx_Srvr * servant,
> 			Ezx_EzxImgObj * Ezximg,
> 			Ezx_EzxRdrDatastoreObj * Ezxstrg,
> 			CORBA_char ** message, CORBA_Environment * ev)
> {
> 	CORBA_short retval = ( CORBA_short )IE_OK;
	
	The problem is; that the ORB for efficiency reasons, will not
initialize your 'out' arguments to contain valid data - that would then
have to detect whether it was overwritten / free it before returning the
values - that would be ghastly ;-) Instead the ORB assumes that for out
arguments and return values - you will return valid data that it can
marshal back (or an exception).

	Thus - this method will blow the ORB's mind when it tries to marshal
the contents of *message (eg.) that is uninitialized - it needs to be a
CORBA_string_dup'ed string; [similarly for any other out args].

	HTH,

		Michael.

-- 
 mmeeks@gnu.org  <><, Pseudo Engineer, itinerant idiot