asudhak asudhak - 2 months ago 12
C Question

HTTP get Request using C WITHOUT libCurl

I want to write a C program to generate a Get Request without using any external libraries. Is this possible using only C libraries, using sockets ? I'm thinking of crafting a http packet(using proper formatting) and sending it to the server. Is this the only possible way or is there a better way ?

Answer

Using BSD sockets or, if you're somewhat limited, say you have some RTOS, some simpler TCP stack, like lwIP, you can form the GET/POST request.

There are a number of open-source implementations. See the "happyhttp" as a sample ( http://scumways.com/happyhttp/happyhttp.html ). I know, it is C++, not C, but the only thing that is "C++-dependant" there is a string/array management, so it is easily ported to pure C.

Beware, there are no "packets", since HTTP is usually transfered over the TCP connection, so technically there is only a stream of symbols in RFC format. Since http requests are usually done in a connect-send-disconnect manner, one might actually call this a "packet".

Basically, once you have an open socket (sockfd) "all" you have to do is something like

char sendline[MAXLINE + 1], recvline[MAXLINE + 1];
char* ptr;

size_t n;

/// Form request
snprintf(sendline, MAXSUB, 
     "GET %s HTTP/1.0\r\n"  // POST or GET, both tested and works. Both HTTP 1.0 HTTP 1.1 works, but sometimes 
     "Host: %s\r\n"     // but sometimes HTTP 1.0 works better in localhost type
     "Content-type: application/x-www-form-urlencoded\r\n"
     "Content-length: %d\r\n\r\n"
     "%s\r\n", page, host, (unsigned int)strlen(poststr), poststr);

/// Write the request
if (write(sockfd, sendline, strlen(sendline))>= 0) 
{
    /// Read the response
    while ((n = read(sockfd, recvline, MAXLINE)) > 0) 
    {
        recvline[n] = '\0';

        if(fputs(recvline,stdout) == EOF) { cout << ("fputs erros"); }
        /// Remove the trailing chars
        ptr = strstr(recvline, "\r\n\r\n");

        // check len for OutResponse here ?
        snprintf(OutResponse, MAXRESPONSE,"%s", ptr);
    }          
}
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