C Web server

webserver.c

// webserver.c
// ./webserver "./script.sh"
//
// Copyright 2023 J.P.H. Bruins Slot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the “Software”), to deal in
// the Software without restriction, including without limitation the rights to
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
// of the Software, and to permit persons to whom the Software is furnished to do
// so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#include <arpa/inet.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#define PORT 8080
#define BUFFER_SIZE 1024

int main(int argc, char* argv[]) {

  char buffer[BUFFER_SIZE];

  // man 7 tcp
  // man socket
  // man sys_socket.h
  int sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (sockfd == -1) {
    // man errno
    // man 3 perror
    perror("webserver (socket)");
    return 1;
  }
  printf("socket created successfully\n");

  // man 7 ip
  struct sockaddr_in host_addr;
  int host_addrlen = sizeof(host_addr);
  
  // man htons
  // man htonl
  host_addr.sin_family = AF_INET;
  host_addr.sin_port = htons(PORT);
  host_addr.sin_addr.s_addr = htonl(INADDR_ANY);

  struct sockaddr_in client_addr;
  int client_addrlen = sizeof(client_addr);

  // man bind
  if (bind(sockfd, (struct sockaddr*)&host_addr, host_addrlen) != 0) {
    perror("webserver (bind)");
    return 1;
  }
  printf("socket successfully bound to address\n");

  // man 2 listen
  if (listen(sockfd, SOMAXCONN) != 0) {
    perror("webserver (listen)");
    return 1;
  }
  printf("server listening for connections\n");

  for (;;) {
    // man 2 accept
    int request =
        accept(sockfd, (struct sockaddr*)&host_addr, (socklen_t*)&host_addrlen);
    if (request < 0) {
      perror("webserver (accept)");
      continue;
    }
    printf("connection accepted\n");

    // man getsockname
    int sockn = getsockname(request, (struct sockaddr*)&client_addr,
                            (socklen_t*)&client_addrlen);
    if (sockn < 0) {
      perror("webserver (getsockname)");
      continue;
    }

    // man 2 read
    int readable = read(request, buffer, BUFFER_SIZE);
    if (readable < 0) {
      perror("webserver (read)");
      continue;
    }

    // man sscanf
    // man inet_ntoa
    // man ntohs
    char method[BUFFER_SIZE], uri[BUFFER_SIZE], version[BUFFER_SIZE];
    sscanf(buffer, "%s %s %s", method, uri, version);
    printf("[%s:%u] %s %s %s\n", inet_ntoa(client_addr.sin_addr),
           ntohs(client_addr.sin_port), method, version, uri);

    // https://developer.chrome.com/blog/private-network-access-preflight/
    // https://wicg.github.io/local-network-access/
    char response[] =
        "HTTP/1.1 200 OK\r\n"
        "Server: webserver-c\r\n"
        "Cache-Control: no-store\r\n"
        "Access-Control-Allow-Origin: *\r\n"
        "Content-type: application/octet-stream\r\n"
        "Access-Control-Allow-Private-Network: true\r\n\r\n";

    // man 2 write
    // man 3 strlen
    int writer = write(request, response, strlen(response));

    if (writer < 0) {
      perror("webserver (write)");
      continue;
    }
    // 441 * 4
    uint8_t writable[1764];
    
    // man popen
    FILE* pipe = popen(argv[1], "r");
    
    for (;;) {
      // man fread
      size_t count = fread(writable, 1, sizeof(writable), pipe);
      int stream = write(request, writable, count);

      if (stream < 0) {
        perror("webserver (write)");
        // man pclose
        pclose(pipe);
        break;
      }
    }
    // man 2 close
    close(request);
    break;
  }
  return 0;
}