[SOLVED] Not receiving all data at server end of UDP socket- suggestions please.

kcleveland · 06-15-2010, 02:12 PM

Hey All-

I've written a UDP server and UDP client for some testing here at work, and I am sending a couple of floats (as a string) from the client to the server, and everything shows up correctly at the server EXCEPT for the first 3 characters of the string- they become strange characters and I cannot explain why.

Here is the relevant server-side code (let me know if you need more):

Code:

...
char rxdgram[1024];

len_inet = sizeof adr_clnt;
   z = recvfrom(s,
   	rxdgram,
   	sizeof rxdgram,
   	0,
	(struct sockaddr *)&adr_clnt,
	&len_inet);
   if (z < 0)
	bail("recvfrom(2)");

printf("%s",rxdgram);
...

and the relevant client-side code:

Code:

char dgram[1024]="0.735844;0.245885;1.343227;0.234825";

z = sendto(s,
	    dgram,
	    strlen(dgram),
	    0,
	    (struct sockaddr *)&adr_srvr,
	    len_inet);
	if ( z < 0 )
	    bail("sendto(2)");

z = strlen(dgram);
	if ( z > 0 && dgram[-z] == '\n' )
	   dgram[z] = 0; /*removes newline*/

and the server printf outputs this:

Code:

�_Z35844;0.245885;1.343227;0.234825

I've tried several novice hacks with no success (changing the data type of the buffer, etc.)- anyone have any suggestions/examples to help me along?

Thanks in advance!

kapsikum · 06-15-2010, 11:55 PM

Can you paste the code which is compilable and runnable directly.

JohnGraham · 06-16-2010, 02:13 AM

Have you had a look at what's going on on-the-wire? That way you'll know if it's a client- or server-side issue. Wireshark is a good tool for that (most major distros have it as a package, though IIRC you may have to install wireshark-gui or something to get a GUI).

kcleveland · 07-02-2010, 10:11 AM

Thanks for your replies everyone-

I got a veteran C programmer at work to help me- turns out that the FFT I was doing on the server side (not posted) had one parameter that was, as they say, "out of bounds" (I forgot about a null terminate on one line).

This is what was causing the final string being sent to be a character or two off, thus resulting in our wierd little characters posted above.