[lwip-users] lwip_send() not sending correct amount of data?
Hi guys,
I have been trying to implement simple client - server apps that will
help me measure communication performance. Server is running on custom
ZYNQ board and is supposed only to send packets, whereas client is
running on PC and is supposed only to receive packets. I am using Lwip
v1.4.1.
This is main loop of server app:
for (i = 0; i < 8000; i++)
{
if ((nsent = send(clisock, sendbuf, TCP_MAX_DATA_LEN, 0)) < 0)
{
xil_printf("send error! %d\r\n", nsent);
break;
}
xil_printf("i: %d, nsent: %d\r\n", i, nsent);
}
send(clisock, sendbuf, 10, 0);
Main loop of client app:
while (1)
{
nrecv = recv(sock, g_recvline, TCP_MAX_DATA_LEN, 0);
if (nrecv < TCP_MAX_DATA_LEN)
break;
}
The problem is that after some number of packets, client app receives
less than TCP_MAX_DATA_LEN (which is 1446) bytes even though it isn't
supposed to receive packet of that size at that moment. For example,
after 1013rd packet sent, client receives packet that is less than 1446.
But, the real problem is that send function always returns 1446! I have
verified at the PC side that there is one packet received that is
smaller then 1446. I am providing capture file (please download it from this
linkhttp://s000.tinyupload.com/?file_id=02107988891904422407
), communication
starts from packet no. 55 (192.168.0.101 is PC, whereas 192.168.0.240 is ZYNQ
board). Than take a look at packet no. 466, I think that is the packet
that confuses client app?
Everything I have described so far is happening when I DON'T have print
xil_printf("i: %d, nsent: %d\r\n", i, nsent) in server app, or when I
only print nsent. But when I put that print, server app works as
expected (wtf?). I have also made applications in which PC is sending
packets, and server is receiving, and in that case everything works as
expected regardless of whether there are some prints or whatever.
What do you think of this problem, I would be really grateful if you
could help me.
Best regards,
Nenad
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Re: [lwip-users] lwip_send() not sending correct amount of data?
pekez wrote: > The problem is that after some number of packets, client app receives > less than TCP_MAX_DATA_LEN (which is 1446) bytes even though it isn't > supposed to receive packet of that size at that moment. For example, > after 1013rd packet sent, client receives packet that is less than 1446. TCP does NOT send packets, it sends a stream. As such, a remote host will receive arbitrary sized chunks. TCP only guarantees to deliver the bytes in the exact order. Are you missing bytes or only complaining about segmentation? > [..] I am providing capture file (please download it from this link I'm really too lazy to do that. Instead, keep your capture file small and your mail won't be rejected again ;-) Simon ___ lwip-users mailing list lwip-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/lwip-users
Re: [lwip-users] lwip_send() not sending correct amount of data?
You are right, bytes are not missing, I just checked. This is not a real problem then, it's just lack of understanding of TCP. :) It was strange at first because I don't have similar problems at all when sending from PC to ZYNQ. When it comes to capture files, I am quite new to that, so I am not really sure how to make them smaller. Any reference about this will be great. Thanks for quick answer! Regards On 5.12.2016 14:24, Simon Goldschmidt wrote: pekez wrote: The problem is that after some number of packets, client app receives less than TCP_MAX_DATA_LEN (which is 1446) bytes even though it isn't supposed to receive packet of that size at that moment. For example, after 1013rd packet sent, client receives packet that is less than 1446. TCP does NOT send packets, it sends a stream. As such, a remote host will receive arbitrary sized chunks. TCP only guarantees to deliver the bytes in the exact order. Are you missing bytes or only complaining about segmentation? [..] I am providing capture file (please download it from this link I'm really too lazy to do that. Instead, keep your capture file small and your mail won't be rejected again ;-) Simon ___ lwip-users mailing list lwip-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/lwip-users ___ lwip-users mailing list lwip-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/lwip-users
Re: [lwip-users] lwip_send() not sending correct amount of data?
You make capture files smaller by capturing at the right time and enabling only the hosts/ports you need to see. You understand TCP by reading Stallings, Comer, Tanenbaum... ;^) The amount of data sent by a TCP stack is what it thinks best for the current scenario, given its configuration. It is like some governments, it knows what is best for us ;^) ___ lwip-users mailing list lwip-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/lwip-users
Re: [lwip-users] lwip_send() not sending correct amount of data?
Sergio, no love for Richard Stevens? You always have constructive advices, I see. :) On 12/5/2016 5:52 PM, Sergio R. Caprile wrote: You make capture files smaller by capturing at the right time and enabling only the hosts/ports you need to see. You understand TCP by reading Stallings, Comer, Tanenbaum... ;^) The amount of data sent by a TCP stack is what it thinks best for the current scenario, given its configuration. It is like some governments, it knows what is best for us ;^) ___ lwip-users mailing list lwip-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/lwip-users --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ lwip-users mailing list lwip-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/lwip-users
