Add the sse-websocket module

sse-websocket/src/main/java/com/ankurm/ssews/WebSocketConfig.java

@@ -0,0 +1,62 @@
+package com.ankurm.ssews;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.messaging.simp.config.MessageBrokerRegistry;
+import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
+import org.springframework.web.socket.config.annotation.StompEndpointRegistry;
+import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer;
+import org.springframework.web.socket.config.annotation.WebSocketTransportRegistration;
+
+/**
+ * Four lines of configuration that decide more than they look like they do.
+ *
+ * @see <a href="../../../../../docs/04-stomp.md">docs/04-stomp.md</a>
+ */
+@Configuration
+@EnableWebSocketMessageBroker
+public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
+
+    @Override
+    public void registerStompEndpoints(StompEndpointRegistry registry) {
+        // No setAllowedOrigins call at all. The handshake then permits same-origin requests
+        // only -- and "same origin" is decided from the Origin header, which a non-browser
+        // client does not send, so curl and the Java client are allowed while a page on
+        // another site is not. Add setAllowedOriginPatterns("https://app.example.com") for a
+        // real cross-origin front end; setAllowedOrigins("*") is rejected outright when
+        // credentials are allowed.
+        registry.addEndpoint("/ws");
+
+        // The SockJS variant is a SECOND endpoint on its own path. Registering .withSockJS()
+        // on the same path does not give you both: SockJS wraps the URL in /{server}/{session}
+        // and a plain WebSocket client pointed at it fails the handshake.
+        registry.addEndpoint("/ws-sockjs").withSockJS();
+    }
+
+    @Override
+    public void configureMessageBroker(MessageBrokerRegistry registry) {
+        // The simple broker. In-memory, single JVM, no persistence, no acknowledgement, and it
+        // drops everything on restart. enableStompBrokerRelay(..) swaps in RabbitMQ or ActiveMQ
+        // without touching a controller -- see ../rabbitmq for the broker side.
+        registry.enableSimpleBroker("/topic", "/queue");
+
+        // Destinations a CLIENT sends to. /app/chat.send is routed to @MessageMapping; anything
+        // starting with /topic or /queue goes straight to the broker and is NEVER seen by a
+        // controller. Getting this backwards produces a message that vanishes with no error.
+        registry.setApplicationDestinationPrefixes("/app");
+
+        // The prefix a client subscribes under for messages addressed to it alone. The client
+        // subscribes to /user/queue/whisper; the broker rewrites that to a session-scoped
+        // destination that no other session can subscribe to.
+        registry.setUserDestinationPrefix("/user");
+    }
+
+    @Override
+    public void configureWebSocketTransport(WebSocketTransportRegistration registration) {
+        // Defaults, restated so the numbers are visible in one place rather than discovered
+        // when a 70 KB frame disappears. WebSocketTransportRegistration's own defaults are
+        // 64 KB for both; see WebSocketLimitsTest for what exceeding them looks like.
+        registration.setMessageSizeLimit(64 * 1024);
+        registration.setSendBufferSizeLimit(512 * 1024);
+        registration.setSendTimeLimit(20_000);
+    }
+}