[lwip-users] RE: Advice on an HTTP conversation

[Tom C. Barker]

For anyone interested....

What I found was that line 5 was a premature close. 4 was a dropped 
packet (at the ip level) and my application erroneously closed the 
connection. Notice that line 10 is the proper response to a received 
request. My well-behaved application now simply waits for ( in this case ) 
another request which checksums properly and is passed up the stack.

2026 > http [SYN] Seq=3726085043 Ack=0 Win=65535 Len=0
http > 2026 [SYN, ACK] Seq=7151 Ack=3726085044 Win=2048 Len=0
2026 > http [ACK] Seq=3726085044 Ack=7152 Win=65535 Len=0
GET /portCh2.gif HTTP/1.1
GET /portCh2.gif HTTP/1.1
http > 2026 [ACK] Seq=7152 Ack=3726085312 Win=1780 Len=0
Continuation
http > 2026 [FIN, ACK] Seq=7358 Ack=3726085312 Win=1780 Len=0
2026 > http [ACK] Seq=3726085312 Ack=7359 Win=65329 Len=0
2026 > http [FIN, ACK] Seq=3726085312 Ack=7359 Win=65329 Len=0
http > 2026 [ACK] Seq=7359 Ack=3726085313 Win=1779 Len=0

Tom
        

-----Original Message-----
From: Tom C. Barker 
Sent: Friday, January 09, 2004 5:04 PM
To: 'Mailing list for lwIP users'
Subject: Advice on an HTTP conversation


Hello,

Following is an Ethereal dump of a request for a graphic. The browser 
requesting the file is IE 6.01. In line 4, "C HTTP GET /titleMIH.gif
HTTP/1.1" 
was corrupted at reception did not pass the checksum routine (ok, fine). 
Next the connection closes. Curiously, the client asks for the file again, 
without ever setting up the connection (so it seems to me). LWIP then 
ACKS a much earlier packet, it seems, and then the conversation folds. 

Could someone offer me an explanation as to what might be happening here
and if there is any necessary tweaking that might go on in the LWIP code
to recover? Any comments to the appropriateness of how the browser is 
acting in this conversation is certainly welcome.

Thanks,
Tom Barker

1  C TCP  2394 > http [SYN] Seq=1716877397 Ack=0 Win=65535 Len=0
2  S TCP  http > 2394 [SYN, ACK] Seq=9296 Ack=1716877398 Win=2048 Len=0
3  C TCP  2394 > http [ACK] Seq=1716877398 Ack=9297 Win=65535 Len=0
4  C HTTP GET /titleMIH.gif HTTP/1.1
5  S TCP  http > 2394 [FIN, ACK] Seq=9297 Ack=1716877398 Win=2048 Len=0
6  C TCP  2394 > http [ACK] Seq=1716877667 Ack=9298 Win=65535 Len=0
7  C TCP  2394 > http [FIN, ACK] Seq=1716877667 Ack=9298 Win=65535 Len=0
8  S TCP  http > 2394 [ACK] Seq=9298 Ack=1716877398 Win=2048 Len=0
9  C HTTP GET /titleMIH.gif HTTP/1.1
10 S TCP  http > 2394 [ACK] Seq=9298 Ack=1716877667 Win=2048 Len=0
11 C TCP  2394 > http [FIN, ACK] Seq=1716877667 Ack=9298 Win=65535 Len=0
12 S TCP  http > 2394 [RST, ACK] Seq=9299 Ack=1716877668 Win=2048 Len=0