Re: [lwip-users] Pulling data from a server using HTTP with lwIP

[Robert Wood]

It's not quite like that, I'm not explaining very well. I'll try again. :~)

If I send the GET command out, then my board does not send the ACK to 
the server for the SYN, SYN ACK, ACK handshake. This is what happens. 
Bear in mind the lwIP board is the client in this case.

Here are two different In both cases I do this in the lwIP client thread:

    IP4_ADDR(&local_ip,emacIPADDR0,emacIPADDR1,emacIPADDR2,emacIPADDR3);
    rc1 = netconn_bind ( xNetConn, &local_ip, 0 );
    IP4_ADDR(&remote_ip,192,168,0,87);
    rc2 = netconn_connect ( xNetConn, &remote_ip, 80 );

Scenario 1:

In this case I do not send a GET request out.

Client -> SYN (Server receives this)
Server -> SYN ACK (Client receives this)
Client -> ACK (Server receives this)

Scenario 2:

In this case I send the GET command out.

Client -> SYN (Server receives this)
Server -> SYN ACK (Client receives this)
Client -> GET Command

So, in scenario 2, the client is not sending out the ACK in the initial 
handshake. I'm assuming it's because I need to wait for the lwIP stack 
to send the ACK. I'm assuming anyway. If that is the case, how does my 
thread know when the stack has sent the ACK to the server and I am at 
liberty to send the GET request?

I hope I've made that clearer. :~)

I'm probably doing naive things because I'm trying to learn a lot of 
stuff at the moment!

On 13/11/14 13:09, Simon Goldschmidt wrote:
> Robert Wood wrote:
> > If I establish a connection from the board to the desktop and do not
> > send a GET request, then lwIP does the SYN, SYN ACK, ACK handshake just
> > fine.
> >
> > If I add the [potentially incorrect] GET request, the SYNN is sent, the
> > SYN ACK is received, but my board running lwIP does not send the ACK out
> > to the desktop.
>
> Does it piggy-back the ACK on your GET request or is the GET request not even 
> sent out? I'd expect to see the GET request along with the handshake-ACK.Then, 
> the webserver will eventually time out waiting for the double-CRLF.
>
> However, if lwIP does not send ANYTHING after receiving the SYN-ACK, there's 
> something wrong... :-/
>
> Simon
>
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