How to make an HTTP get request in C without libcurl?

Sending an HTTP GET request in C without libraries such as libcurl requires low-level socket programming. This process involves creating and configuring sockets, establishing a connection to the target server, and manually sending crafted HTTP requests. Below is a basic step-by-step guide and example code using socket functions from the standard C library to accomplish this task:

Steps

1. Initialize the socket library (required only on Windows systems):

   • Windows systems require initializing WSA (Windows Sockets API) using the WSAStartup function.

2. Create a socket:

   • Use the socket function to create a socket. For HTTP, TCP protocol is typically used, so the socket type is SOCK_STREAM and the protocol is IPPROTO_TCP.

3. Connect to the server:

   • Use gethostbyname to resolve the server's IP address.
   • Use the connect function to establish a connection to the server's specific port (HTTP typically uses port 80).

4. Send the HTTP GET request:

   • Manually construct a simple HTTP GET request string.
   • Use the send function to transmit the request to the server.

5. Receive the response:

   • Use the recv function to receive the response from the server.
   • Process or output the response data.

6. Close the socket:

   • Use closesocket on Windows or close on UNIX/Linux to close the socket.

7. Cleanup the socket library (required only on Windows systems):

   • Use the WSACleanup function.

Example Code

c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#ifdef _WIN32
#include <winsock2.h>
#else
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>
#endif

int main() {
#ifdef _WIN32
    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
        fprintf(stderr, "WSAStartup failed.\n");
        return 1;
    }
#endif

    int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sock < 0) {
        perror("Socket creation failed");
        return 1;
    }

    struct hostent *server = gethostbyname("example.com");
    if (server == NULL) {
        fprintf(stderr, "Host resolution failed.\n");
        return 1;
    }

    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    memcpy(&serv_addr.sin_addr.s_addr, server->h_addr, server->h_length);
    serv_addr.sin_port = htons(80);

    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        perror("Connection failed");
        return 1;
    }

    char *message = "GET / HTTP/1.1\r\nHost: example.com\r\n\r\n";
    if (send(sock, message, strlen(message), 0) < 0) {
        perror("Send failed");
        return 1;
    }

    char response[4096];
    if (recv(sock, response, sizeof(response), 0) < 0) {
        perror("Receive failed");
        return 1;
    }

    printf("Server response: %s\n", response);

    close(sock);
#ifdef _WIN32
    WSACleanup();
#endif
    return 0;
}

In this example, we manually construct an HTTP GET request and send it via sockets. Note that this approach requires a thorough understanding of the HTTP protocol and TCP/IP, particularly when dealing with more complex HTTP requests and responses. In commercial and production environments, for security and usability, it is generally recommended to use established libraries such as libcurl.