fix: change SSE connection setting and resolve SSE CORS errors #121

Author: hyni03

backend/src/main/java/com/example/backend/config/SecurityConfig.java

@@ -12,7 +12,6 @@
 import org.springframework.web.cors.CorsConfigurationSource;
 import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
 
-import java.util.Arrays;
 import java.util.List;
 
 @Configuration
@@ -36,9 +35,10 @@ public SecurityFilterChain filterChain(HttpSecurity httpSecurity) throws Excepti
     public CorsConfigurationSource corsConfigurationSource() {
         CorsConfiguration configuration = new CorsConfiguration();
         configuration.setAllowedOrigins(List.of(allowedOrigins)); // 프론트엔드 도메인
-        configuration.setAllowedMethods(Arrays.asList("GET", "POST", "PUT", "DELETE", "OPTIONS", "HEAD")); // 허용할 HTTP 메서드
-        configuration.setAllowedHeaders(Arrays.asList("Authorization", "Content-Type", "Last-Event-ID")); // 허용할 헤더
-        configuration.setExposedHeaders(Arrays.asList("Authorization", "Content-Type", "Cache-Control", "Last-Event-ID")); // 응답에서 노출할 헤더
+
+        configuration.setAllowedMethods(List.of("GET", "POST", "PUT", "DELETE", "OPTIONS", "HEAD"));
+        configuration.setAllowedHeaders(List.of("Authorization", "Content-Type", "Last-Event-ID"));
+        configuration.setExposedHeaders(List.of("Authorization", "Content-Type", "Cache-Control", "Last-Event-ID"));
         configuration.setAllowCredentials(true); // 자격 증명 포함 요청 허용
 
         UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();

backend/src/main/java/com/example/backend/dashboard/controller/CaseDetectController.java

@@ -4,15 +4,16 @@
 import com.example.backend.dashboard.dto.CaseDetectResponse;
 import com.example.backend.dashboard.service.CaseDetectService;
 import com.example.backend.dashboard.service.SseEmitterService;
+import jakarta.servlet.http.HttpServletResponse;
 import lombok.RequiredArgsConstructor;
+import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.*;
 import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;
 
 @RestController
 @RequestMapping("/api/v1/case")
 @RequiredArgsConstructor
-@CrossOrigin("${cors.allowed-origins}")
 public class CaseDetectController {
 
     private final CaseDetectService caseDetectService;
@@ -25,8 +26,13 @@ public ResponseEntity<?> detectAlarm(@RequestBody CaseDetectRequest request) {
         return ResponseEntity.ok(response);
     }
 
-    @GetMapping("/subscribe")
-    public SseEmitter subscribe() {
+    @GetMapping(value = "/subscribe", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
+    public SseEmitter subscribe(HttpServletResponse response) {
+
+        response.setHeader("Cache-Control", "no-cache");
+        response.setHeader("X-Accel-Buffering", "no"); // Nginx 버퍼링 해제
+        response.setHeader("Connection", "keep-alive"); // 명시적 Keep-Alive
+
         return sseEmitterService.createEmitter();
     }
 

backend/src/main/java/com/example/backend/dashboard/service/SseEmitterService.java

@@ -1,4 +1,5 @@
 package com.example.backend.dashboard.service;
+
 import com.example.backend.dashboard.dto.CaseDetectResponse;
 import org.springframework.http.MediaType;
 import org.springframework.stereotype.Service;
@@ -7,7 +8,7 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.*;
 
 @Service
 public class SseEmitterService {
@@ -18,20 +19,45 @@ public SseEmitter createEmitter() {
         SseEmitter emitter = new SseEmitter(Long.MAX_VALUE);
         emitters.add(emitter);
 
-        emitter.onCompletion(() -> emitters.remove(emitter));
-        emitter.onTimeout(() -> emitters.remove(emitter));
+        emitter.onCompletion(() -> {
+            emitters.remove(emitter);
+            System.out.println("[SseEmitterService] Emitter completed. Current count = " + emitters.size());
+        });
+
+        emitter.onTimeout(() -> {
+            emitters.remove(emitter);
+            System.out.println("[SseEmitterService] Emitter timed out. Current count = " + emitters.size());
+        });
+
+        emitter.onError((e) -> {
+            emitters.remove(emitter);
+            System.out.println("[SseEmitterService] Emitter error: " + e.getMessage());
+        });
+
+        try {
+            emitter.send(SseEmitter.event().name("connect").data("SSE connection established!"));
+            System.out.println("[SseEmitterService] Sent initial 'connect' event.");
+        } catch (IOException e) {
+            emitters.remove(emitter);
+            System.out.println("[SseEmitterService] Failed to send initial event: " + e.getMessage());
+        }
+
         return emitter;
     }
 
     public void broadcast(CaseDetectResponse response) {
         List<SseEmitter> deadEmitters = new ArrayList<>();
+
         for (SseEmitter emitter : emitters) {
             try {
                 emitter.send(SseEmitter.event()
                         .name("alarm-detected")
-                        .data(response, MediaType.APPLICATION_JSON));
+                        .data(response, MediaType.APPLICATION_JSON)
+                );
+                System.out.println("  -> [alarm-detected] sent to " + emitter);
             } catch (IOException e) {
                 deadEmitters.add(emitter);
+                System.out.println("  -> Failed to send to Emitter: " + emitter);
             }
         }
         emitters.removeAll(deadEmitters);