[Spread-users] BUFFER_TOO_SHORT && endian_mismatch >= 0

Tim Peters tim at zope.com
Wed Jul 3 15:41:06 EDT 2002

[Jonathan Stanton]
> endian_mismatch can in general be negative, 0 or 1. The negative cases
> only occur when the BUFFER_TOO_SHORT error also occurs. Otherwise
> endian_mismatch should be 0 or 1. It will be 0 for membership messages
> and when the endianness of the sender is the same as that of the
> receiver. It will be 1 when the sending machine (where the client runs)
> has a different endianness from the receiving machine (where the
> receiving client runs).
> So I'm not sure if that answers the question. If you are saying that
> endian_mismatch is 0 when you also got a BUFFER_TOO_SHORT error then
> that shouldn't occur I think.

Us either <wink>.  We don't know what the endian_mismatch value is
specifically, only that SP_receive() returned BUFFER_TOO_SHORT and
endian_mismatch was not negative then.  The code is like this:

	for (;;) {
		size = SP_receive(self->mbox, &svc_type,
				  max_groups, &num_groups, groups,
				  &msg_type, &endian,
				  bufsize, pbuffer);

		if (size >= 0) {
			if (num_groups < 0) {
				/* XXX This really happens!
				   Don't dare retry the receive, since we
				   didn't get an error.  The extra names
				   are forever lost. */
				num_groups = max_groups;
		if (size == BUFFER_TOO_SHORT) {
			if (endian >= 0)
				goto set_error;      THIS BRANCH IS GETTING TAKEN
			bufsize = -endian;
			data = PyString_FromStringAndSize(NULL, bufsize);
			if (data == NULL)
				goto error;
			pbuffer = PyString_AS_STRING(data);
		if (size == GROUPS_TOO_SHORT) {
			if (num_groups >= 0)
				goto set_error;
			max_groups = -num_groups;

> You can get a GROUPS_TOO_SHORT with an endian_mismatch of 0 though. That
> just means that the groups buffer is too short but the main message body
> buffer is big enough.

I believe that.  I cut off our GROUPS_TOO_SHORT code above because it isn't
relevant, but it doesn't look at endian_mismatch.

> Does this help?

A little, in confirming that what we're seeing isn't possible <wink>.  Our
evidence comes from crash log files at a user's site; we haven't yet been
able to provoke it ourselves.  Thanks for the confirmation!  More when we
know more.

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