proxy.c

#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <arpa/inet.h>

int get_proxy_socket(void) {
  int fd = socket(AF_INET, SOCK_STREAM, 0);

  struct sockaddr_in bind_address;
  bind_address.sin_family = AF_INET;
  bind_address.sin_port = htons(8080);
  bind_address.sin_addr.s_addr = INADDR_ANY;

  bind(fd, & bind_address, sizeof(bind_address));
  listen(fd, 1024);

  return fd;
}

int fix_crlf_endings(char * buf, int len) {
  int ret = len;

  for (int i = 0; i < len; i++) {
    if (buf[i] == '\r' && buf[i + 1] == '\n') {
      buf[i] = '\n';

      /* SUPER PEDANTIC! */
      for (int j = i + 1; j < len; j++)
        buf[j] = buf[j + 1];
      ret--;
    }
  }

  return ret;
}

int main(int args, char ** argv) {
  int in_len, out_len, real_out, out_fd, in_fd, listen_fd = get_proxy_socket();
  struct sockaddr_in to_address;
  char buf[32768];

  to_address.sin_family = AF_INET;
  to_address.sin_port = htons(80);
  to_address.sin_addr.s_addr = inet_addr("10.0.0.1"); /* This worked for me - YMMV */

  while (1) {
    in_fd = accept4(listen_fd, NULL, 0, 0);
    if (fork())
      continue;
    out_fd = socket(AF_INET, SOCK_STREAM, 0);
    connect(out_fd, & to_address, sizeof(to_address));

    if (fork()) {
      while (1) {
        in_len = read(in_fd, & buf, 1460);
        if (in_len <= 0) return 0;
        out_len = fix_crlf_endings( & buf, in_len);
        if (write(out_fd, & buf, out_len) <= 0) return 0;
      }
    } else {
      while (1) {
        if (read(out_fd, & buf, 1460) <= 0) return 0;
        if (write(in_fd, & buf, 1460) <= 0) return 0;
      }
    }
  }

  return 0;
}