How to connect a socket to an http server through proxy? - c++

Question

Recently I wrote a program using sockets in C, to connect to an HTTP server running locally and thereby to do requests to that.
That worked fine for me. After that I tried the same code to connect to another server on the web (e.g. www.google.com), but I was not able to connect and was getting another html response from the proxy server in my network.
My local IP is: 10.0.2.58
The proxy IP is: 10.0.0.1
This is the response I got :
HTTP/1.1 302 Found
Expires: Fri, 10 Feb 2012 12:47:35 GMT
Expires: 0
Cache-Control: max-age=180000
Cache-Control: no-store, no-cache, must-revalidate
Cache-Control: post-check=0, pre-check=0
Pragma: no-cache
Connection: close
Location: http://10.0.0.1:8000/index.php?redirurl=http%3A%2F%2F10.0.2.58%2F
Content-type: text/html
Content-Length: 0
Date: Wed, 08 Feb 2012 10:47:35 GMT
Server: lighttpd/1.4.29
How can I bypass this proxy to connect to external servers?
Response got when tried with CONNECT
HTTP/1.1 302 Found
Expires: Fri, 10 Feb 2012 13:37:58 GMT
Expires: 0
Cache-Control: max-age=180000
Cache-Control: no-store, no-cache, must-revalidate
Cache-Control: post-check=0, pre-check=0
Pragma: no-cache
Connection: close
Location: http://10.0.0.1:8000/index.php?redirurl=http%3A%2F%2F10.0.2.58http%3A%2F%2Fwww.google.com%2F
Content-type: text/html
Content-Length: 0
Date: Wed, 08 Feb 2012 11:37:58 GMT
Server: lighttpd/1.4.29
Working code which connect's to my local apache
#include<unistd.h>
#include<stdio.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<netdb.h>
#include<string.h>
#define MAX_BUFFER_SIZE 1024
int main(int argc,char *argv[])
{
int clsd,ssd,status;
char buffer[1024];
char request[]="GET / HTTP/1.1\r\nHost:10.0.2.58\r\n\r\n";
struct sockaddr_in srvr_addr;
struct addrinfo hints,*res;
srvr_addr.sin_family=AF_INET;
srvr_addr.sin_port=htons(80);
srvr_addr.sin_addr.s_addr=inet_addr("10.0.2.58");//Local server
clsd =socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
if(clsd<=0)
{
perror("Socket init failed..\n");return 1;
}
ssd=connect(clsd,(struct sockaddr *)&srvr_addr,(socklen_t)(sizeof srvr_addr));
if(clsd<=0)
{
perror("Socket connect failed..\n");return 1;
}
write(clsd,request,strlen(request));
memset((void *)&request,0x00,strlen(request));
memset(&buffer,0x00,MAX_BUFFER_SIZE);
do
{
status=read(clsd,&buffer,MAX_BUFFER_SIZE);
write(1,&buffer,status);
memset((void *)&request,0x00,strlen(request));
memset(&buffer,0x00,MAX_BUFFER_SIZE);
do
{
status=read(clsd,&buffer,MAX_BUFFER_SIZE);
write(1,&buffer,status);
}while(status>0);
close(clsd);
return 0;
}

Answer 1

To use connections via proxy (or if they are implicitly proxy-fied), first you should connect to proxy, send a 'CONNECT' message with target host; proxy will establish connection and return you data.
Here is in steps:
open socket to proxy host
send 'CONNECT http://www.google.com:80 HTTP/1.0\r\n\r\n' string
wait for recv
You must specify protocol (in our case is HTTP 1.0, non-chunked) with ending newline characters, so proxy knows how to communicate with end point.
You can find details about CONNECT method at http://www.ietf.org/rfc/rfc2817.txt

Answer 2

If you're specifically trying to bypass the proxy, you should talk to whoever administers your network to find out if that's even possible. If your first block of output is an attempt to connect to Google then it appears to me that there's some kind of transparent proxy on your network that you'll have to take special (and network-specific) steps to bypass.
Of course, if you're just interested in getting data, you could try following the redirect...