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

[Robert Wood]

Ah, no, I wasn't aware of that at all.

I still don't know how I'd do that as, if left to its own devices, the 
stack sends the ACK out anyway and I have no idea how I'd tack that data 
on to the ACK.

It seems like the low level stuff does take care of that for you. Is it 
the case that I can poll something to wait for the stack to inform me 
that the ACK has gone out and I can send stuff or am I looking at it the 
wrong way?

Thanks,

Rob

On 13/11/14 13:31, Simon Goldschmidt wrote:
> Robert,
> are you aware that it's legal for the ACK you are missing to contain
> data also? In this case the packets would look like this:
> SYN ->
> <- SYN/ACK
> ACK+DATA(GET) ->
> This is what I was trying to explain in my last mail...
> Simon
> *Gesendet:* Donnerstag, 13. November 2014 um 14:22 Uhr
> *Von:* "Robert Wood" <address@hidden>
> *An:* address@hidden
> *Betreff:* Re: [lwip-users] Pulling data from a server using HTTP with lwIP
> 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
>  >
>  > _______________________________________________
>  > lwip-users mailing list
>  > address@hidden
>  > https://lists.nongnu.org/mailman/listinfo/lwip-users
>  >
>
> _______________________________________________
> lwip-users mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/lwip-users
>
>
> _______________________________________________
> lwip-users mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/lwip-users