Re: [lwip-users] http server problems/bug

[Noam Weissman]

Hi,

Every socket has a sender part and a receiver part. Normally it is full duplex !.

TCP has layers. Some data is handled inside the TCP stack MAC + L1 and some is

handled in L2,L3 etc...

When an ACK or some other low level message arrives it is handled inside the TCP

and never get to the upper layers.

I do not know the exact internal mechanism but what I know that when you call tcp_close

it shuts down the sender and receiver handling inside the TCP stack for the open connection.

It frees any internal memory and deletes the related PCB.

If you shut down the sender only using tcp shutdown function the connection is still is open for

the receiver part. That means that is the remote side closes your tcp_recv call back will be triggered

with data that has ZERO length. Also the TCP stack will respond (low level) to that message by acknowledging it.

http://stackoverflow.com/questions/4160347/close-vs-shutdown-socket

BR,

Noam.

c - close vs shutdown socket? - Stack Overflow stackoverflow.com In C, I understood that if we close a socket, it means the socket will be destroyed and can be re-used later. How about shutdown? The description said it closes half ...

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From: lwip-users <lwip-users-bounces+address@hidden> on behalf of lampo <address@hidden>
Sent: Saturday, August 6, 2016 6:37 AM
To: address@hidden
Subject: Re: [lwip-users] http server problems/bug

 

> On LwIP side when you close a connection using the tcp_close it closes
> ALL.

Does that mean it closes all other connections including other independent
threads,like tcp client ,tcp server in our multithreaded system?


> From having problems in some TCP module that I wrote I found that if I
> call tcp_shutdown and only
> define shutdown the TX side the connection is closed only after getting
> the ACK.

sorry,I can't quite get it. In our example, you mean TX side is our web
server, RX side is browser from PC, right?    But browser has already
got the ack from web server after it sends out FIN,and close the
connection,while in fact the TX side does not closed totally.

can you show the process in following format ,so I can get it precisely?

 web server                       <------ GET  HTTP/1.1-----   web Client
 web server (FIN_WAIT_1)  -------- FIN,PSH----------->   web Client
 web server (FIN_WAIT_2)  <-------- ACK-------------      web Client
 (web server will stay in FIN_WAIT_2 for we find it receives no ACK here )
 web server                     <-------- FIN--------------      web Client
 web server                      -------- ACK------------->      web Client
(web client receives the ack, so it  close the RX side connection, thus it
cannot respond to a  FIN now)




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View this message in context: http://lwip.100.n7.nabble.com/http-server-problems-bug-tp27017p27032.html

lwip-users - http server problems/bug

lwip.100.n7.nabble.com

http server problems/bug. With more infomation provided, I re-post it here(I post it through nabble before), sorry for that. Problem, web server <------ GET HTTP/1.1----- ...

Sent from the lwip-users mailing list archive at Nabble.com.

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