text: /***************************************************************************
   *                                  _   _ ____  _
   *  Project                     ___| | | |  _ \| |
   *                             / __| | | | |_) | |
   *                            | (__| |_| |  _ <| |___
   *                             \___|\___/|_| \_\_____|
   *
   * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
   *
   * This software is licensed as described in the file COPYING, which
   * you should have received as part of this distribution. The terms
   * are also available at https://curl.haxx.se/docs/copyright.html.
   *
   * You may opt to use, copy, modify, merge, publish, distribute and/or sell
   * copies of the Software, and permit persons to whom the Software is
   * furnished to do so, under the terms of the COPYING file.
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
   * KIND, either express or implied.
   *
   ***************************************************************************/
  
  /* <DESC>
   * multi_socket API using libuv
   * </DESC>
   */
  /* Example application using the multi socket interface to download multiple
     files in parallel, powered by libuv.
  
     Requires libuv and (of course) libcurl.
  
     See https://nikhilm.github.com/uvbook/ for more information on libuv.
  */
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <uv.h>
  #include <curl/curl.h>
  
  uv_loop_t *loop;
  CURLM *curl_handle;
  uv_timer_t timeout;
  
  typedef struct curl_context_s {
    uv_poll_t poll_handle;
    curl_socket_t sockfd;
  } curl_context_t;
  
  curl_context_t* create_curl_context(curl_socket_t sockfd)
  {
    curl_context_t *context;
  
    context = (curl_context_t *) malloc(sizeof *context);
  
    context->sockfd = sockfd;
  
    uv_poll_init_socket(loop, &context->poll_handle, sockfd);
    context->poll_handle.data = context;
  
    return context;
  }
  
  void curl_close_cb(uv_handle_t *handle)
  {
    curl_context_t *context = (curl_context_t *) handle->data;
    free(context);
  }
  
  void destroy_curl_context(curl_context_t *context)
  {
    uv_close((uv_handle_t *) &context->poll_handle, curl_close_cb);
  }
  
  void add_download(const char *url, int num)
  {
    char filename[50];
    FILE *file;
    CURL *handle;
  
    snprintf(filename, 50, "%d.download", num);
  
    file = fopen(filename, "wb");
    if(!file) {
      fprintf(stderr, "Error opening %s\n", filename);
      return;
    }
  
    handle = curl_easy_init();
    curl_easy_setopt(handle, CURLOPT_WRITEDATA, file);
    curl_easy_setopt(handle, CURLOPT_PRIVATE, file);
    curl_easy_setopt(handle, CURLOPT_URL, url);
    curl_multi_add_handle(curl_handle, handle);
    fprintf(stderr, "Added download %s -> %s\n", url, filename);
  }
  
  static void check_multi_info(void)
  {
    char *done_url;
    CURLMsg *message;
    int pending;
    CURL *easy_handle;
    FILE *file;
  
    while((message = curl_multi_info_read(curl_handle, &pending))) {
      switch(message->msg) {
      case CURLMSG_DONE:
        /* Do not use message data after calling curl_multi_remove_handle() and
           curl_easy_cleanup(). As per curl_multi_info_read() docs:
           "WARNING: The data the returned pointer points to will not survive
           calling curl_multi_cleanup, curl_multi_remove_handle or
           curl_easy_cleanup." */
        easy_handle = message->easy_handle;
  
        curl_easy_getinfo(easy_handle, CURLINFO_EFFECTIVE_URL, &done_url);
        curl_easy_getinfo(easy_handle, CURLINFO_PRIVATE, &file);
        printf("%s DONE\n", done_url);
  
        curl_multi_remove_handle(curl_handle, easy_handle);
        curl_easy_cleanup(easy_handle);
        if(file) {
          fclose(file);
        }
        break;
  
      default:
        fprintf(stderr, "CURLMSG default\n");
        break;
      }
    }
  }
  
  void curl_perform(uv_poll_t *req, int status, int events)
  {
    int running_handles;
    int flags = 0;
    curl_context_t *context;
  
    uv_timer_stop(&timeout);
  
    if(events & UV_READABLE)
      flags |= CURL_CSELECT_IN;
    if(events & UV_WRITABLE)
      flags |= CURL_CSELECT_OUT;
  
    context = (curl_context_t *) req->data;
  
    curl_multi_socket_action(curl_handle, context->sockfd, flags,
                             &running_handles);
  
    check_multi_info();
  }
  
  void on_timeout(uv_timer_t *req, int status)
  {
    int running_handles;
    curl_multi_socket_action(curl_handle, CURL_SOCKET_TIMEOUT, 0,
                             &running_handles);
    check_multi_info();
  }
  
  void start_timeout(CURLM *multi, long timeout_ms, void *userp)
  {
    if(timeout_ms <= 0)
      timeout_ms = 1; /* 0 means directly call socket_action, but we'll do it in
                         a bit */
    uv_timer_start(&timeout, on_timeout, timeout_ms, 0);
  }
  
  int handle_socket(CURL *easy, curl_socket_t s, int action, void *userp,
                    void *socketp)
  {
    curl_context_t *curl_context;
    int events = 0;
  
    switch(action) {
    case CURL_POLL_IN:
    case CURL_POLL_OUT:
    case CURL_POLL_INOUT:
      curl_context = socketp ?
        (curl_context_t *) socketp : create_curl_context(s);
  
      curl_multi_assign(curl_handle, s, (void *) curl_context);
  
      if(action != CURL_POLL_IN)
        events |= UV_WRITABLE;
      if(action != CURL_POLL_OUT)
        events |= UV_READABLE;
  
      uv_poll_start(&curl_context->poll_handle, events, curl_perform);
      break;
    case CURL_POLL_REMOVE:
      if(socketp) {
        uv_poll_stop(&((curl_context_t*)socketp)->poll_handle);
        destroy_curl_context((curl_context_t*) socketp);
        curl_multi_assign(curl_handle, s, NULL);
      }
      break;
    default:
      abort();
    }
  
    return 0;
  }
  
  int main(int argc, char **argv)
  {
    loop = uv_default_loop();
  
    if(argc <= 1)
      return 0;
  
    if(curl_global_init(CURL_GLOBAL_ALL)) {
      fprintf(stderr, "Could not init cURL\n");
      return 1;
    }
  
    uv_timer_init(loop, &timeout);
  
    curl_handle = curl_multi_init();
    curl_multi_setopt(curl_handle, CURLMOPT_SOCKETFUNCTION, handle_socket);
    curl_multi_setopt(curl_handle, CURLMOPT_TIMERFUNCTION, start_timeout);
  
    while(argc-- > 1) {
      add_download(argv[argc], argc);
    }
  
    uv_run(loop, UV_RUN_DEFAULT);
    curl_multi_cleanup(curl_handle);
  
    return 0;
  }
  