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Server Sent Events example - issue esp8266#7008
Illustrates the use of SSE using ESP8266WebServer
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‎libraries/ESP8266WebServer/examples/ServerSentEvents/ServerSentEvents.ino

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/* Simple Server Sent Event (aka EventSource) demo
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Run demo as follows:
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1. set SSID, password and ports, compile and run program
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you should see (random) updates of sensors A and B
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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"
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on both server and client, you should now see that your client is registered
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the server sends back the location of the event bus (channel) to the client:
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subscription for client IP <your client's IP address>: event bus location: http://<your ESP IP>:<your port + 1>/rest/events
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you will also see that the sensors are ready to broadcast state changes, but the client is not yet listening:
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SSEBroadcastState - client <your client IP>> registered but not listening
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3. on the client, start listening for events with: curl -sS "http://<your ESP IP>:<your port + 1>/rest/events"
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if all is well, the following is being displayed on the ESP console
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SSEHandler - registered client with IP <your client IP address> is listening...
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broadcast status change to client IP <your client IP>> for sensor[A|B] with new state <some number>>
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every minute you will see on the ESP: SSEKeepAlive - client is still connected
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on the client, you should see the SSE messages coming in:
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event: event
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data: { "TYPE":"KEEP-ALIVE" }
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event: event
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data: { "TYPE":"STATE", "sensorB": {"state" : 12408, "prevState": 13502} }
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event: event
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data: { "TYPE":"STATE", "sensorA": {"state" : 17664, "prevState": 49362} }
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4. on the client, stop listening by hitting control-C
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on the ESP, after maximum one minute, the following message is displayed: SSEKeepAlive - client no longer connected, remove subscription
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if you start listening again after the time expired, the "/rest/events" handle becomes stale and "Handle not found" is returned
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you can also try to start listening again before the KeepAliver timer expires or simply register your client again
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*/
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extern "C" {
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#include "c_types.h"
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}
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#include <ESP8266WiFi.h>
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#include <WiFiClient.h>
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#include <ESP8266WebServer.h>
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#include <ESP8266mDNS.h>
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#include <Ticker.h>
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#ifndef STASSID
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//#define STASSID "your-ssid"
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//#define STAPSK "your-password"
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#define STASSID "EThomeZX"
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#define STAPSK "superd0me;0rca"
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#endif
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const char* ssid = STASSID;
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const char* password = STAPSK;
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const unsigned int port = 80;
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ESP8266WebServer server(port);
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ESP8266WebServer SSEserver(port + 1);
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struct SSESubscription {
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uint32_t clientIP;
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WiFiClient client;
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Ticker keepAliveTimer;
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} subscription; // in this simplified example, only one SSE client subscription allowed
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unsigned short sensorA = 0, sensorB = 0; //Simulate two sensors
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Ticker update, updateA, updateB;
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void notFound(ESP8266WebServer &server) {
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Serial.println(F("Handle not found"));
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String message = "Handle Not Found\n\n";
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message += "URI: ";
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message += server.uri();
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message += "\nMethod: ";
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message += (server.method() == HTTP_GET) ? "GET" : "POST";
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message += "\nArguments: ";
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message += server.args();
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message += "\n";
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for (uint8_t i = 0; i < server.args(); i++) {
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message += " " + server.argName(i) + ": " + server.arg(i) + "\n";
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}
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server.send(404, "text/plain", message);
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}
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void handleNotFound() { notFound(server); }
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void handleSSENotFound() { notFound(SSEserver); }
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void SSEBroadcastState(const char *sensorName, unsigned short prevSensorValue, unsigned short sensorValue) {
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if (!subscription.clientIP) return;
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WiFiClient client = subscription.client;
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if (client.connected()) {
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Serial.printf_P(PSTR("broadcast status change to client IP %s for %s with new state %d\n"),
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IPAddress(subscription.clientIP).toString().c_str(), sensorName, sensorValue);
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client.printf_P(PSTR("event: event\ndata: { \"TYPE\":\"STATE\", \"%s\": {\"state\" : %d, \"prevState\": %d} }\n"),
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sensorName, sensorValue, prevSensorValue);
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} else
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Serial.printf_P(PSTR("SSEBroadcastState - client %s registered but not listening\n"), IPAddress(subscription.clientIP).toString().c_str());
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}
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void SSEKeepAlive(SSESubscription *s) {
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SSESubscription &subscription = *s;
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if (!subscription.clientIP) return;
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WiFiClient client = subscription.client;
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if (client.connected()) {
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Serial.println(F("SSEKeepAlive - client is still connected"));
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client.println(F("event: event\ndata: { \"TYPE\":\"KEEP-ALIVE\" }"));
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} else {
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Serial.println(F("SSEKeepAlive - client no longer connected, remove subscription"));
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subscription.keepAliveTimer.detach();
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client.flush();
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client.stop();
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subscription.clientIP = 0;
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}
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}
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// SSEHandler handles the client connection to the event bus (client event listener)
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// every 60 seconds it sends a keep alive event via Ticker
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void SSEHandler(SSESubscription *s) {
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WiFiClient client = SSEserver.client();
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SSESubscription &subscription = *s;
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if (subscription.clientIP != uint32_t(client.remoteIP())) { // IP addresses don't match, reject this client
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Serial.printf_P(PSTR("SSEHandler - unregistered client with IP %s tries to listen\n"), SSEserver.client().remoteIP().toString().c_str());
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return notFound(SSEserver);
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}
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//client.setNoDelay(true); // Any of these will crash the ESP (Soft WDT reset)
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//client.setSync(true);
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Serial.printf_P(PSTR("SSEHandler - registered client with IP %s is listening...\n"), IPAddress(subscription.clientIP).toString().c_str());
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subscription.client = client; // capture SSE server client connection
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SSEserver.setContentLength(CONTENT_LENGTH_UNKNOWN); // the payload can go on forever
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subscription.keepAliveTimer.attach(30.0, std::bind(SSEKeepAlive, s)); // Refresh time every 30s for demo
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}
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// Simulate sensors
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void updateSensor(const char* name, unsigned short *value) {
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unsigned short newVal = (unsigned short)RANDOM_REG32; // (not so good) random value for the sensor
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unsigned short val = *value;
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Serial.printf_P(PSTR("update sensor %s - previous state: %d, new state: %d\n"), name, val, newVal);
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if (val != newVal) SSEBroadcastState(name, newVal, val); // only broadcast if state is different
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*value = newVal;
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update.once(rand() % 20 + 10, std::bind(updateSensor, name, value)); // randomly update sensor A
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}
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void handleSubscribe() {
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IPAddress clientIP = server.client().remoteIP(); // get IP address of client
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String SSEurl = F("http://");
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SSEurl += WiFi.localIP().toString();
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SSEurl += F(":");
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SSEurl += port + 1;
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size_t offset = SSEurl.length();
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SSEurl += F("/rest/events");
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if (subscription.clientIP != (uint32_t) clientIP) { // Allocate new subscription
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subscription = {(uint32_t) clientIP, SSEserver.client(), Ticker()};
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SSEserver.on(SSEurl.substring(offset), std::bind(SSEHandler, &subscription));
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} else
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Serial.print(F("reusing "));
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Serial.printf_P(PSTR("subscription for client IP %s: event bus location: %s\n"), clientIP.toString().c_str(), SSEurl.c_str());
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server.send_P(200, "text/plain", SSEurl.c_str());
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}
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void startServers() {
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server.on(F("/rest/events/subscribe"), handleSubscribe);
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server.onNotFound(handleNotFound);
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server.begin();
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Serial.println("HTTP server started");
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SSEserver.onNotFound(handleSSENotFound);
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//SSEserver.keepCurrentClient(true); // Looks like it is not needed
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SSEserver.begin();
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Serial.println("HTTP SSE EventSource server started");
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}
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void setup(void) {
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Serial.begin(115200);
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WiFi.mode(WIFI_STA);
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WiFi.begin(ssid, password);
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Serial.println("");
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while (WiFi.status() != WL_CONNECTED) { // Wait for connection
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delay(500);
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Serial.print(".");
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}
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Serial.printf_P(PSTR("\nConnected to %s with IP address: %s\n"), ssid, WiFi.localIP().toString().c_str());
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if (MDNS.begin("esp8266"))
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Serial.println("MDNS responder started");
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startServers(); // start web and SSE servers
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updateSensor("sensorA", &sensorA);
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updateSensor("sensorB", &sensorB);
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}
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void loop(void) {
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server.handleClient();
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SSEserver.handleClient();
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MDNS.update();
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yield();
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}

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