freertos: lws_cancel_service udp as pipe

Freertos + lwip doesn't support pipe2() or pipe()... implement a "pipe"
based on two UDP sockets, one listening on 127.0.0.1:54321 and the other
doing a sendto() there of a single byte to interrupt the event loop wait.

Re-use the arrangements for actual pipe fds and pipe role to deliver
lws_cancel_service() functionality using this.

lib/core-net/vhost.c

@@ -881,9 +881,14 @@ lws_create_event_pipes(struct lws_context *context)
 	 * not bound to a vhost or protocol (both are NULL)
 	 */
 
+#if LWS_MAX_SMP > 1
 	for (n = 0; n < context->count_threads; n++) {
+#else
+	n = 0;
+	{
+#endif
 		if (context->pt[n].pipe_wsi)
-			continue;
+			return 0;
 
 		wsi = lws_zalloc(sizeof(*wsi), "event pipe wsi");
 		if (!wsi) {
@@ -900,7 +905,7 @@ lws_create_event_pipes(struct lws_context *context)
 		context->pt[n].pipe_wsi = wsi;
 		context->count_wsi_allocated++;
 
-		if (lws_plat_pipe_create(wsi))
+		if (!lws_plat_pipe_create(wsi)) {
 			/*
 			 * platform code returns 0 if it actually created pipes
 			 * and initialized pt->dummy_pipe_fds[].  If it used
@@ -909,17 +914,17 @@ lws_create_event_pipes(struct lws_context *context)
 			 * related to dummy_pipe_fds[], adding it to the fds,
 			 * etc.
 			 */
-			continue;
 
-		wsi->desc.sockfd = context->pt[n].dummy_pipe_fds[0];
-		lwsl_debug("event pipe fd %d\n", wsi->desc.sockfd);
+			wsi->desc.sockfd = context->pt[n].dummy_pipe_fds[0];
+			lwsl_debug("event pipe fd %d\n", wsi->desc.sockfd);
 
-		if (context->event_loop_ops->sock_accept)
-			if (context->event_loop_ops->sock_accept(wsi))
+			if (context->event_loop_ops->sock_accept)
+				if (context->event_loop_ops->sock_accept(wsi))
+					return 1;
+
+			if (__insert_wsi_socket_into_fds(context, wsi))
 				return 1;
-
-		if (__insert_wsi_socket_into_fds(context, wsi))
-			return 1;
+		}
 	}
 
 	return 0;

lib/core/context.c

@@ -619,10 +619,8 @@ lws_create_context(const struct lws_context_creation_info *info)
 				goto bail;
 		}
 
-#if !defined(LWS_AMAZON_RTOS)
 	if (lws_create_event_pipes(context))
 		goto bail;
-#endif
 #endif
 
 	lws_context_init_ssl_library(info);

lib/core/private-lib-core.h

@@ -314,6 +314,10 @@ struct lws_context {
 	lws_retry_bo_t	default_retry;
 	lws_sorted_usec_list_t sul_system_state;
 
+#if defined(LWS_PLAT_FREERTOS)
+	struct sockaddr_in frt_pipe_si;
+#endif
+
 #if defined(LWS_WITH_HTTP2)
 	struct http2_settings set;
 #endif

lib/plat/freertos/freertos-pipe.c

@@ -1,7 +1,7 @@
 /*
  * libwebsockets - small server side websockets and web server implementation
  *
- * Copyright (C) 2010 - 2019 Andy Green <andy@warmcat.com>
+ * Copyright (C) 2010 - 2020 Andy Green <andy@warmcat.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to
@@ -27,16 +27,81 @@
 int
 lws_plat_pipe_create(struct lws *wsi)
 {
+	struct lws_context_per_thread *pt = &wsi->context->pt[(int)wsi->tsi];
+	struct sockaddr_in *si = &wsi->context->frt_pipe_si;
+	lws_sockfd_type *fd = pt->dummy_pipe_fds;
+
+	/*
+	 * There's no pipe abstraction on lwip / freertos... use a UDP socket
+	 * listening on 127.0.0.1:54321 and send a byte to it from a second UDP
+	 * socket to cancel the wait.
+	 */
+
+	fd[0] = socket(AF_INET, SOCK_DGRAM, 0);
+	if (fd[0] < 0)
+		goto bail;
+
+	fd[1] = socket(AF_INET, SOCK_DGRAM, 0);
+	if (fd[1] < 0)
+		goto bail;
+
+	/*
+	 * No need for memset since it's in zalloc'd context... it's in the
+	 * context so we can reuse the prepared sockaddr to send tp fd[0] whem
+	 * we want to cancel the wait
+	 */
+
+	si->sin_family = AF_INET;
+	si->sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+	si->sin_port = htons(54321);
+
+	if (bind(fd[0], (const struct sockaddr *)si, sizeof(*si)) < 0)
+		goto bail;
+
+	return 0;
+
+bail:
+	lwsl_err("%s: failed\n", __func__);
+
 	return 1;
 }
 
 int
 lws_plat_pipe_signal(struct lws *wsi)
 {
-	return 1;
+	struct lws_context_per_thread *pt = &wsi->context->pt[(int)wsi->tsi];
+	struct sockaddr_in *si = &wsi->context->frt_pipe_si;
+	lws_sockfd_type *fd = pt->dummy_pipe_fds;
+	uint8_t u = 0;
+	int n;
+
+	/*
+	 * Send a single UDP byte payload to the listening socket fd[0], forcing
+	 * the event loop wait to wake.  fd[1] and context->frt_pipe_si are
+	 * set at context creation and are static, the UDP sendto is supposed to
+	 * be threadsafe for lwip:
+	 *
+	 * https://lwip.fandom.com/wiki/LwIP_and_multithreading
+	 *
+	 * Sockets generally can't be used by more than one application thread
+	 * (on udp/raw netconn, doing a sendto/recv is currently possible).
+	 */
+
+	n = sendto(fd[1], &u, 1, 0, (struct sockaddr *)si, sizeof(*si));
+
+	return n != 1;
 }
 
 void
 lws_plat_pipe_close(struct lws *wsi)
 {
+	struct lws_context_per_thread *pt = &wsi->context->pt[(int)wsi->tsi];
+	lws_sockfd_type *fd = pt->dummy_pipe_fds;
+
+	if (fd[0] && fd[0] != -1)
+		close(fd[0]);
+	if (fd[1] && fd[1] != -1)
+		close(fd[1]);
+
+	fd[0] = fd[1] = -1;
 }