Server Sent Events example - issue esp8266#7008

Illustrates the use of SSE using ESP8266WebServer

libraries/ESP8266WebServer/examples/ServerSentEvents/ServerSentEvents.ino

@@ -0,0 +1,191 @@
+/* Simple 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, 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 + 1>/rest/events
+
+     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, start listening for events with: curl -sS "http://<your ESP IP>:<your port + 1>/rest/events"
+     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"
+#define STASSID "EThomeZX"
+#define STAPSK  "superd0me;0rca"
+#endif
+
+const char* ssid = STASSID;
+const char* password = STAPSK;
+const unsigned int port = 80;
+
+ESP8266WebServer server(port);
+ESP8266WebServer SSEserver(port + 1);
+
+struct SSESubscription {
+  uint32_t clientIP;
+  WiFiClient client;
+  Ticker keepAliveTimer;
+} subscription; // in this simplified example, only one SSE client subscription allowed
+
+unsigned short sensorA = 0, sensorB = 0;   //Simulate two sensors
+Ticker update, updateA, updateB;
+
+void notFound(ESP8266WebServer &server) {
+  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 handleNotFound() { notFound(server); }
+void handleSSENotFound() { notFound(SSEserver); }
+
+void SSEBroadcastState(const char *sensorName, unsigned short prevSensorValue, unsigned short sensorValue) {
+  if (!subscription.clientIP) return;
+  WiFiClient client = subscription.client;
+  if (client.connected()) {
+    Serial.printf_P(PSTR("broadcast status change to client IP %s for %s with new state %d\n"), 
+    IPAddress(subscription.clientIP).toString().c_str(), sensorName, sensorValue);  
+    client.printf_P(PSTR("event: event\ndata: { \"TYPE\":\"STATE\", \"%s\": {\"state\" : %d, \"prevState\": %d} }\n"),
+      sensorName, sensorValue, prevSensorValue);
+  } else
+    Serial.printf_P(PSTR("SSEBroadcastState - client %s registered but not listening\n"), IPAddress(subscription.clientIP).toString().c_str());
+}
+
+void SSEKeepAlive(SSESubscription *s) {
+  SSESubscription &subscription = *s;
+  if (!subscription.clientIP) return;
+  WiFiClient client = subscription.client;  
+  if (client.connected()) {
+    Serial.println(F("SSEKeepAlive - client is still connected"));
+    client.println(F("event: event\ndata: { \"TYPE\":\"KEEP-ALIVE\" }"));
+  } else { 
+    Serial.println(F("SSEKeepAlive - client no longer connected, remove subscription"));
+    subscription.keepAliveTimer.detach();
+    client.flush();
+    client.stop();
+    subscription.clientIP = 0;
+  }
+}
+
+// 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(SSESubscription *s) {
+  WiFiClient client = SSEserver.client();
+  SSESubscription &subscription = *s;
+  if (subscription.clientIP != uint32_t(client.remoteIP())) { // IP addresses don't match, reject this client
+    Serial.printf_P(PSTR("SSEHandler - unregistered client with IP %s tries to listen\n"), SSEserver.client().remoteIP().toString().c_str());
+    return notFound(SSEserver);
+  }  
+  //client.setNoDelay(true);  // Any of these will crash the ESP (Soft WDT reset)
+  //client.setSync(true);
+  Serial.printf_P(PSTR("SSEHandler - registered client with IP %s is listening...\n"), IPAddress(subscription.clientIP).toString().c_str());
+  subscription.client = client; // capture SSE server client connection
+  SSEserver.setContentLength(CONTENT_LENGTH_UNKNOWN); // the payload can go on forever
+  subscription.keepAliveTimer.attach(30.0, std::bind(SSEKeepAlive, s));  // Refresh time every 30s for demo
+}
+
+// Simulate sensors
+void updateSensor(const char* name, unsigned short *value) {
+  unsigned short newVal = (unsigned short)RANDOM_REG32; // (not so good) random value for the sensor
+  unsigned short val = *value;
+  Serial.printf_P(PSTR("update sensor %s - previous state: %d, new state: %d\n"), name, val, newVal);
+  if (val != newVal) SSEBroadcastState(name, newVal, val); // only broadcast if state is different
+  *value = newVal;
+  update.once(rand() % 20 + 10, std::bind(updateSensor, name, value));  // randomly update sensor A 
+}
+
+void handleSubscribe() {
+  IPAddress clientIP = server.client().remoteIP();   // get IP address of client
+  String SSEurl = F("http://");
+  SSEurl += WiFi.localIP().toString();
+  SSEurl += F(":");
+  SSEurl += port + 1;
+  size_t offset = SSEurl.length();
+  SSEurl += F("/rest/events");
+
+  if (subscription.clientIP != (uint32_t) clientIP) {  // Allocate new subscription
+    subscription = {(uint32_t) clientIP, SSEserver.client(), Ticker()};
+    SSEserver.on(SSEurl.substring(offset), std::bind(SSEHandler, &subscription));
+  } else
+    Serial.print(F("reusing "));  
+  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(handleNotFound);
+  server.begin();
+  Serial.println("HTTP server started");
+  SSEserver.onNotFound(handleSSENotFound);
+  //SSEserver.keepCurrentClient(true);  // Looks like it is not needed
+  SSEserver.begin();
+  Serial.println("HTTP SSE EventSource server 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
+  updateSensor("sensorA", &sensorA);
+  updateSensor("sensorB", &sensorB);
+}
+
+void loop(void) {
+  server.handleClient();
+  SSEserver.handleClient();
+  MDNS.update();
+  yield();
+}