[lwip-users] Using lwip for writing a minimal HTTP proxy

[Mandeep Sandhu]

Hi All,

I'm implementing a very minimal HTTP proxy server, using lwIP (1.3.1)
in "sequential" mode.

I've based my code on the sample http webserver that is provided along
with lwIP (httpd_sequential.c). I'm using ecos.
The way the server works is simple. Eg: A request like http://<my
IP>/local/index.html from client, will cause it to serve a local page.
Whereas  http://<my IP>/REMOTE/index.html will cause it to "proxy" the
client request to another HTTP server (pre-configured).

I'm able to do the local part successfully, i.e server local content
(the index.html response is created on the fly, it's not a file).

The problem starts when I try to proxy the request to another server.

Say the clients connection with my server is "client_conn". In the
main event loop of my server, for proxy requests, I do the following:

1) proxy_conn = netconn_new(NETCONN_TCP);
2) netconn_connect( proxy_conn, <IP addr of other server>, <other
server's listening port> );
3) netconn_write( proxy_conn, <data to be proxied>, <length>, NETCONN_COPY);

4) Listen for resp (this code is based on the TCP echo example):
    while ((proxy_resp = netconn_recv(proxy_conn)) != NULL ) {
        do {
            netbuf_data(proxy_resp, &data, &len);
            //Write response to the client
            err = netconn_write(client_conn, data, len, NETCONN_COPY);

            if (err != ERR_OK) {
                goto error; // some error handler
            }
        } while (netbuf_next(proxy_resp) >= 0);
        netbuf_delete(proxy_resp);
    }

My problem happens at step 2. The error code returned is "-5" i.e ERR_ABRT.

Is this the right approach to do this? Why is the "connect" failing?
Is it because in sequential mode I cannot initiate a second TCP
connection while the first one is not closed?

I'm new to TCP, so pardon me if I'm missing something obvious! :)

Thanks,
-mandeep