docs: added multi-event.c example

Similar to multi-uv.c but using libevent 2. This is a simpler libevent
integration example then hiperfifo.c.

Closes #4471

docs/examples/Makefile.inc

@@ -45,4 +45,4 @@ COMPLICATED_EXAMPLES = curlgtk.c curlx.c htmltitle.cpp cacertinmem.c \
   sampleconv.c synctime.c threaded-ssl.c evhiperfifo.c \
   smooth-gtk-thread.c version-check.pl href_extractor.c asiohiper.cpp \
   multi-uv.c xmlstream.c usercertinmem.c sessioninfo.c \
-  threaded-shared-conn.c crawler.c ephiperfifo.c
+  threaded-shared-conn.c crawler.c ephiperfifo.c multi-event.c

docs/examples/multi-event.c

@@ -0,0 +1,240 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2018, 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 libevent
+ * </DESC>
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <event2/event.h>
+#include <curl/curl.h>
+
+struct event_base *base;
+CURLM *curl_handle;
+struct event *timeout;
+
+typedef struct curl_context_s {
+  struct event *event;
+  curl_socket_t sockfd;
+} curl_context_t;
+
+static void curl_perform(int fd, short event, void *arg);
+
+static curl_context_t* create_curl_context(curl_socket_t sockfd)
+{
+  curl_context_t *context;
+
+  context = (curl_context_t *) malloc(sizeof(*context));
+
+  context->sockfd = sockfd;
+
+  context->event = event_new(base, sockfd, 0, curl_perform, context);
+
+  return context;
+}
+
+static void destroy_curl_context(curl_context_t *context)
+{
+  event_del(context->event);
+  event_free(context->event);
+  free(context);
+}
+
+static 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;
+    }
+  }
+}
+
+static void curl_perform(int fd, short event, void *arg)
+{
+  int running_handles;
+  int flags = 0;
+  curl_context_t *context;
+
+  if(event & EV_READ)
+    flags |= CURL_CSELECT_IN;
+  if(event & EV_WRITE)
+    flags |= CURL_CSELECT_OUT;
+
+  context = (curl_context_t *) arg;
+
+  curl_multi_socket_action(curl_handle, context->sockfd, flags,
+                           &running_handles);
+
+  check_multi_info();
+}
+
+static void on_timeout(evutil_socket_t fd, short events, void *arg)
+{
+  int running_handles;
+  curl_multi_socket_action(curl_handle, CURL_SOCKET_TIMEOUT, 0,
+                           &running_handles);
+  check_multi_info();
+}
+
+static int start_timeout(CURLM *multi, long timeout_ms, void *userp)
+{
+  if(timeout_ms < 0) {
+    evtimer_del(timeout);
+  }
+  else {
+    if(timeout_ms == 0)
+      timeout_ms = 1; /* 0 means directly call socket_action, but we'll do it
+                         in a bit */
+    struct timeval tv;
+    tv.tv_sec = timeout_ms / 1000;
+    tv.tv_usec = (timeout_ms % 1000) * 1000;
+    evtimer_del(timeout);
+    evtimer_add(timeout, &tv);
+  }
+  return 0;
+}
+
+static 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 |= EV_WRITE;
+    if(action != CURL_POLL_OUT)
+      events |= EV_READ;
+
+    events |= EV_PERSIST;
+
+    event_del(curl_context->event);
+    event_assign(curl_context->event, base, curl_context->sockfd, events,
+      curl_perform, curl_context);
+    event_add(curl_context->event, NULL);
+
+    break;
+  case CURL_POLL_REMOVE:
+    if(socketp) {
+      event_del(((curl_context_t*) socketp)->event);
+      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)
+{
+  if(argc <= 1)
+    return 0;
+
+  if(curl_global_init(CURL_GLOBAL_ALL)) {
+    fprintf(stderr, "Could not init curl\n");
+    return 1;
+  }
+
+  base = event_base_new();
+  timeout = evtimer_new(base, on_timeout, NULL);
+
+  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);
+  }
+
+  event_base_dispatch(base);
+
+  curl_multi_cleanup(curl_handle);
+  event_free(timeout);
+  event_base_free(base);
+
+  libevent_global_shutdown();
+  curl_global_cleanup();
+
+  return 0;
+}