Added data push over WS example

examples/webui-push-ws/main.c

@@ -0,0 +1,54 @@
+// Copyright (c) 2020 Cesanta Software Limited
+// All rights reserved
+//
+// Example Websocket server with timers. This is a simple Websocket echo
+// server, which sends a message to all connected clients periodically,
+// using timer API.
+
+#include "mongoose.h"
+
+static const char *s_listen_on = "http://localhost:8000";
+static const char *s_web_root = "web_root";
+
+static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
+  if (ev == MG_EV_HTTP_MSG) {
+    struct mg_http_message *hm = (struct mg_http_message *) ev_data;
+    if (mg_http_match_uri(hm, "/api/watch")) {
+      mg_ws_upgrade(c, hm, NULL);  // Upgrade HTTP to Websocket
+      c->label[0] = 'W';           // Set some unique mark on the connection
+    } else {
+      struct mg_http_serve_opts opts = {.root_dir = s_web_root};
+      mg_http_serve_dir(c, ev_data, &opts);
+    }
+  }
+  (void) fn_data;
+}
+
+// Push to all watchers
+static void push(struct mg_mgr *mgr, const char *name, const void *data) {
+  struct mg_connection *c;
+  for (c = mgr->conns; c != NULL; c = c->next) {
+    if (c->label[0] != 'W') continue;
+    mg_ws_printf(c, WEBSOCKET_OP_TEXT, "{%Q:%Q,%Q:%Q}", "name", name, "data",
+                 data);
+  }
+}
+
+static void timer_fn(void *arg) {
+  struct mg_mgr *mgr = (struct mg_mgr *) arg;
+  char buf[50];
+  mg_snprintf(buf, sizeof(buf), "[%lu, %d]", (unsigned long) time(NULL),
+              10 + (int) ((double) rand() * 10 / RAND_MAX));
+  push(mgr, "metrics", buf);
+}
+
+int main(void) {
+  struct mg_mgr mgr;  // Event manager
+  mg_mgr_init(&mgr);  // Initialise event manager
+  mg_log_set("2");    // Set debug log level
+  mg_timer_add(&mgr, 2000, MG_TIMER_REPEAT, timer_fn, &mgr);
+  mg_http_listen(&mgr, s_listen_on, fn, NULL);  // Create HTTP listener
+  for (;;) mg_mgr_poll(&mgr, 500);              // Infinite event loop
+  mg_mgr_free(&mgr);                            // Free manager resources
+  return 0;
+}