Re: [lwip-users] tcp_sndbuf return 0 when sending file

[vincent cui]

Hi simon:

 

When I receive tcp packet from client, I found that tcp payload is 970 and 490 by calling following code

 

                   for (q = p; q != NULL; q = q->next)

                   {  

                            UINT len;  

                            printf(" tcp payload len : %d \n", q->len);

                            f_write(fsd->fil, q->payload, q->len, &len);

                            tot_len += len;  

                            if (len != q->len)  

                                     break;  

                   } 

 

And TCP_MSS is  (1500 �C 40). So tcp received packet maximum data is 1460 (970 + 490),

I wonder to know that there is a way to extend the value ? change TCP_MSS to 2048 ?

 

Vincent Cui
Software Engineer Leader
Mobile: +8613255150315
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From: lwip-users-bounces+address@hidden [mailto:lwip-users-bounces+address@hidden On Behalf Of address@hidden
Sent: 2012年4月13日 2:05
To: Mailing list for lwIP users
Subject: Re: [lwip-users] tcp_sndbuf return 0 when sending file

 

vincent cui wrote:

All

 

I develop a FTP server with lwIP 1.3.2 in Cortex M3 platform, when I use FlashFXP to get file from the server, the tcp_sndbuf always return 0 after work a while .

I capture it with wireshark, the file is attached file. The server ip: 192.168.1.51. it seems that transfer error and need retransmission.

>From the wireshark capture, I cannot see why the segment is retransmitted. Also, at which point do you get tcp_sndbuf==0, and what's the size of tcp_sndbuf initially?

I'm afraid that doesn't really help on your problem, though :-(
If I were you, I'd first have a look at lwip_stats to see if there are dropped segments or memory (allocation) failures and then monitor the value of tcp_sndbuf() (maybe it keeps getting smaller and never grows again?).

My sendcode in server is below:

[..]

            err = tcp_write(pcb, fsd->fifo.buffer + i, (u16_t)(fsd->fifo.size - i), 1); 

Yikes! Using numbers instead of constants is really a thing people should learn (I'm speaking of TCP_WRITE_FLAG_COPY vs. '1')!

We provide the constants for people to use them so we are free to modify what they are defined to. By using '1' instead of TCP_WRITE_FLAG_COPY, you have successfully made your code susceptible to problems with future versions of lwIP (once we decide to change the value of TCP_WRITE_FLAG_COPY) :-)

Simon