Server Sent Events example - issue #7008 (#7012)

* Server Sent Events example - issue #7008

Illustrates the use of SSE using ESP8266WebServer

* Update ServerSentEvents.ino

* Create ServerSentEventsMultiClient.ino

* sync

* Update ServerSentEvents.ino

* Update ServerSentEvents.ino

Fix  missing variables in printf statments
Fix subscriptioncount not decreasing
Fix SSEBroadcastState (argument sequence wrong)

* Undo the library additions, move to current master

* Fix compiler warning

* Address review and fix multi-sensor updates

Address points of @devyte's code review:
* Use IPAddress vs. uint32_t
* Refactor the URL parsing logic to use strlen vs. sizeof, since there
  was some confusion in the original (correct) version
* Minimize copies of WiFiClients while in use
* Use byref access for sensor updates

Fix multi-sensor updates
* Create an update Ticker for each sensor, because the original code
  only had one whose callback was overridden by sensorB, meaning sensorA
  never changed

* Fix IPv6 build errors

* Remove WiFiClient extraneous copy

Avoid duplicating WiFiClient by using the WiFiClient object embedded in
the subscriber[] array instead.

Co-authored-by: Earle F. Philhower, III <[email protected]>

Author: ewaldc

libraries/ESP8266WebServer/examples/ServerSentEvents/ServerSentEvents.ino

@@ -0,0 +1,223 @@
+/* Multi-client Server Sent Event (aka EventSource) demo
+  Run demo as follows:
+  1. set SSID, password and ports, compile and run program
+     you should see (random) updates of sensors A and B
+
+  2. on the client(s), register it for the event bus using a REST API call: curl -sS "http://<your ESP IP>:<your port>/rest/events/subscribe"
+     on both server and client, you should now see that your client is registered
+     the server sends back the location of the event bus (channel) to the client:
+      subscription for client IP <your client's IP address>: event bus location: http://<your ESP IP>:<your port>/rest/events/<channel>
+
+     you will also see that the sensors are ready to broadcast state changes, but the client is not yet listening:
+      SSEBroadcastState - client <your client IP>> registered but not listening
+
+  3. on the client(s), start listening for events with: curl -sS "http://<your ESP IP>:<your port>/rest/events/<channel>"
+     if all is well, the following is being displayed on the ESP console
+      SSEHandler - registered client with IP <your client IP address> is listening...
+      broadcast status change to client IP <your client IP>> for sensor[A|B] with new state <some number>>
+     every minute you will see on the ESP: SSEKeepAlive - client is still connected
+
+     on the client, you should see the SSE messages coming in:
+      event: event
+      data: { "TYPE":"KEEP-ALIVE" }
+      event: event
+      data: { "TYPE":"STATE", "sensorB": {"state" : 12408, "prevState": 13502} }
+      event: event
+      data: { "TYPE":"STATE", "sensorA": {"state" : 17664, "prevState": 49362} }
+
+  4. on the client, stop listening by hitting control-C
+    on the ESP, after maximum one minute, the following message is displayed: SSEKeepAlive - client no longer connected, remove subscription
+    if you start listening again after the time expired, the "/rest/events" handle becomes stale and "Handle not found" is returned
+    you can also try to start listening again before the KeepAliver timer expires or simply register your client again
+*/
+
+extern "C" {
+#include "c_types.h"
+}
+#include <ESP8266WiFi.h>
+#include <WiFiClient.h>
+#include <ESP8266WebServer.h>
+#include <ESP8266mDNS.h>
+#include <Ticker.h>
+
+#ifndef STASSID
+#define STASSID "your-ssid"
+#define STAPSK  "your-password"
+#endif
+
+const char* ssid = STASSID;
+const char* password = STAPSK;
+const unsigned int port = 80;
+
+ESP8266WebServer server(port);
+
+#define SSE_MAX_CHANNELS 8  // in this simplified example, only eight SSE clients subscription allowed
+struct SSESubscription {
+  IPAddress clientIP;
+  WiFiClient client;
+  Ticker keepAliveTimer;
+} subscription[SSE_MAX_CHANNELS];
+uint8_t subscriptionCount = 0;
+
+typedef struct {
+  const char *name;
+  unsigned short value;
+  Ticker update;
+} sensorType;
+sensorType sensor[2];
+
+void handleNotFound() {
+  Serial.println(F("Handle not found"));
+  String message = "Handle Not Found\n\n";
+  message += "URI: ";
+  message += server.uri();
+  message += "\nMethod: ";
+  message += (server.method() == HTTP_GET) ? "GET" : "POST";
+  message += "\nArguments: ";
+  message += server.args();
+  message += "\n";
+  for (uint8_t i = 0; i < server.args(); i++) {
+    message += " " + server.argName(i) + ": " + server.arg(i) + "\n";
+  }
+  server.send(404, "text/plain", message);
+}
+
+void SSEKeepAlive() {
+  for (uint8_t i = 0; i < SSE_MAX_CHANNELS; i++) {
+    if (!(subscription[i].clientIP)) {
+      continue;
+    }
+    if (subscription[i].client.connected()) {
+      Serial.printf_P(PSTR("SSEKeepAlive - client is still listening on channel %d\n"), i);
+      subscription[i].client.println(F("event: event\ndata: { \"TYPE\":\"KEEP-ALIVE\" }\n"));   // Extra newline required by SSE standard
+    } else {
+      Serial.printf_P(PSTR("SSEKeepAlive - client not listening on channel %d, remove subscription\n"), i);
+      subscription[i].keepAliveTimer.detach();
+      subscription[i].client.flush();
+      subscription[i].client.stop();
+      subscription[i].clientIP = INADDR_NONE;
+      subscriptionCount--;
+    }
+  }
+}
+
+// SSEHandler handles the client connection to the event bus (client event listener)
+// every 60 seconds it sends a keep alive event via Ticker
+void SSEHandler(uint8_t channel) {
+  WiFiClient client = server.client();
+  SSESubscription &s = subscription[channel];
+  if (s.clientIP != client.remoteIP()) { // IP addresses don't match, reject this client
+    Serial.printf_P(PSTR("SSEHandler - unregistered client with IP %s tries to listen\n"), server.client().remoteIP().toString().c_str());
+    return handleNotFound();
+  }
+  client.setNoDelay(true);
+  client.setSync(true);
+  Serial.printf_P(PSTR("SSEHandler - registered client with IP %s is listening\n"), IPAddress(s.clientIP).toString().c_str());
+  s.client = client; // capture SSE server client connection
+  server.setContentLength(CONTENT_LENGTH_UNKNOWN); // the payload can go on forever
+  server.sendContent_P(PSTR("HTTP/1.1 200 OK\nContent-Type: text/event-stream;\nConnection: keep-alive\nCache-Control: no-cache\nAccess-Control-Allow-Origin: *\n\n"));
+  s.keepAliveTimer.attach_scheduled(30.0, SSEKeepAlive);  // Refresh time every 30s for demo
+}
+
+void handleAll() {
+  const char *uri = server.uri().c_str();
+  const char *restEvents = PSTR("/rest/events/");
+  if (strncmp_P(uri, restEvents, strlen_P(restEvents))) {
+    return handleNotFound();
+  }
+  uri += strlen_P(restEvents); // Skip the "/rest/events/" and get to the channel number
+  unsigned int channel = atoi(uri);
+  if (channel < SSE_MAX_CHANNELS) {
+    return SSEHandler(channel);
+  }
+  handleNotFound();
+};
+
+void SSEBroadcastState(const char *sensorName, unsigned short prevSensorValue, unsigned short sensorValue) {
+  for (uint8_t i = 0; i < SSE_MAX_CHANNELS; i++) {
+    if (!(subscription[i].clientIP)) {
+      continue;
+    }
+    String IPaddrstr = IPAddress(subscription[i].clientIP).toString();
+    if (subscription[i].client.connected()) {
+      Serial.printf_P(PSTR("broadcast status change to client IP %s on channel %d for %s with new state %d\n"),
+                      IPaddrstr.c_str(), i, sensorName, sensorValue);
+      subscription[i].client.printf_P(PSTR("event: event\ndata: {\"TYPE\":\"STATE\", \"%s\":{\"state\":%d, \"prevState\":%d}}\n\n"),
+                                      sensorName, sensorValue, prevSensorValue);
+    } else {
+      Serial.printf_P(PSTR("SSEBroadcastState - client %s registered on channel %d but not listening\n"), IPaddrstr.c_str(), i);
+    }
+  }
+}
+
+// Simulate sensors
+void updateSensor(sensorType &sensor) {
+  unsigned short newVal = (unsigned short)RANDOM_REG32; // (not so good) random value for the sensor
+  Serial.printf_P(PSTR("update sensor %s - previous state: %d, new state: %d\n"), sensor.name, sensor.value, newVal);
+  if (sensor.value != newVal) {
+    SSEBroadcastState(sensor.name, sensor.value, newVal);  // only broadcast if state is different
+  }
+  sensor.value = newVal;
+  sensor.update.once(rand() % 20 + 10, std::bind(updateSensor, sensor));  // randomly update sensor
+}
+
+void handleSubscribe() {
+  if (subscriptionCount == SSE_MAX_CHANNELS - 1) {
+    return handleNotFound();  // We ran out of channels
+  }
+
+  uint8_t channel;
+  IPAddress clientIP = server.client().remoteIP();   // get IP address of client
+  String SSEurl = F("http://");
+  SSEurl += WiFi.localIP().toString();
+  SSEurl += F(":");
+  SSEurl += port;
+  size_t offset = SSEurl.length();
+  SSEurl += F("/rest/events/");
+
+  ++subscriptionCount;
+  for (channel = 0; channel < SSE_MAX_CHANNELS; channel++) // Find first free slot
+    if (!subscription[channel].clientIP) {
+      break;
+    }
+  subscription[channel] = {clientIP, server.client(), Ticker()};
+  SSEurl += channel;
+  Serial.printf_P(PSTR("Allocated channel %d, on uri %s\n"), channel, SSEurl.substring(offset).c_str());
+  //server.on(SSEurl.substring(offset), std::bind(SSEHandler, &(subscription[channel])));
+  Serial.printf_P(PSTR("subscription for client IP %s: event bus location: %s\n"), clientIP.toString().c_str(), SSEurl.c_str());
+  server.send_P(200, "text/plain", SSEurl.c_str());
+}
+
+void startServers() {
+  server.on(F("/rest/events/subscribe"), handleSubscribe);
+  server.onNotFound(handleAll);
+  server.begin();
+  Serial.println("HTTP server and  SSE EventSource started");
+}
+
+void setup(void) {
+  Serial.begin(115200);
+  WiFi.mode(WIFI_STA);
+  WiFi.begin(ssid, password);
+  Serial.println("");
+  while (WiFi.status() != WL_CONNECTED) {   // Wait for connection
+    delay(500);
+    Serial.print(".");
+  }
+  Serial.printf_P(PSTR("\nConnected to %s with IP address: %s\n"), ssid, WiFi.localIP().toString().c_str());
+  if (MDNS.begin("esp8266")) {
+    Serial.println("MDNS responder started");
+  }
+
+  startServers();   // start web and SSE servers
+  sensor[0].name = "sensorA";
+  sensor[1].name = "sensorB";
+  updateSensor(sensor[0]);
+  updateSensor(sensor[1]);
+}
+
+void loop(void) {
+  server.handleClient();
+  MDNS.update();
+  yield();
+}