feat(chat): Polly TTS 음성 캐싱 및 DynamoDB 최적화 refs #8

chatting/ChatFunction/build.gradle

@@ -31,6 +31,9 @@ dependencies {
     // JSON Processing
     implementation 'com.google.code.gson:gson:2.10.1'
 
+    // Password Hashing
+    implementation 'org.mindrot:jbcrypt:0.4'
+
     // Logging
     implementation 'com.amazonaws:aws-lambda-java-log4j2:1.6.0'
     implementation 'org.apache.logging.log4j:log4j-api:2.22.1'

chatting/ChatFunction/src/main/java/com/mzc/secondproject/serverless/chatting/handler/ChatMessageHandler.java

@@ -77,6 +77,8 @@ private APIGatewayProxyResponseEvent handlePost(APIGatewayProxyRequestEvent requ
                 .sk("MSG#" + now + "#" + messageId)
                 .gsi1pk("USER#" + userId)
                 .gsi1sk("MSG#" + now)
+                .gsi2pk("MSG#" + messageId)        // GSI2: messageId로 직접 조회용
+                .gsi2sk("ROOM#" + roomId)
                 .messageId(messageId)
                 .roomId(roomId)
                 .userId(userId)
@@ -87,11 +89,8 @@ private APIGatewayProxyResponseEvent handlePost(APIGatewayProxyRequestEvent requ
 
         ChatMessage savedMessage = chatMessageService.saveMessage(message);
 
-        // 채팅방 lastMessageAt 업데이트
-        chatRoomRepository.findById(roomId).ifPresent(room -> {
-            room.setLastMessageAt(now);
-            chatRoomRepository.save(room);
-        });
+        // 채팅방 lastMessageAt 업데이트 (UpdateExpression으로 1회 호출)
+        chatRoomRepository.updateLastMessageAt(roomId, now);
 
         logger.info("Message sent: {} in room: {}", messageId, roomId);
         return createResponse(201, ApiResponse.success("Message sent", savedMessage));

chatting/ChatFunction/src/main/java/com/mzc/secondproject/serverless/chatting/handler/ChatRoomHandler.java

@@ -9,6 +9,7 @@
 import com.mzc.secondproject.serverless.chatting.dto.ApiResponse;
 import com.mzc.secondproject.serverless.chatting.model.ChatRoom;
 import com.mzc.secondproject.serverless.chatting.repository.ChatRoomRepository;
+import org.mindrot.jbcrypt.BCrypt;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -108,7 +109,7 @@ private APIGatewayProxyResponseEvent createRoom(APIGatewayProxyRequestEvent requ
                 .currentMembers(1)  // 방장 포함
                 .maxMembers(maxMembers)
                 .isPrivate(isPrivate)
-                .password(isPrivate ? password : null)
+                .password(isPrivate && password != null ? BCrypt.hashpw(password, BCrypt.gensalt()) : null)
                 .createdBy(createdBy)
                 .createdAt(now)
                 .lastMessageAt(now)
@@ -203,9 +204,11 @@ private APIGatewayProxyResponseEvent joinRoom(APIGatewayProxyRequestEvent reques
 
         ChatRoom room = optRoom.get();
 
-        // 비밀번호 확인
-        if (room.getIsPrivate() && !room.getPassword().equals(password)) {
-            return createResponse(403, ApiResponse.error("Invalid password"));
+        // 비밀번호 확인 (BCrypt 해시 검증)
+        if (room.getIsPrivate()) {
+            if (password == null || room.getPassword() == null || !BCrypt.checkpw(password, room.getPassword())) {
+                return createResponse(403, ApiResponse.error("Invalid password"));
+            }
         }
 
         // 인원 확인

chatting/ChatFunction/src/main/java/com/mzc/secondproject/serverless/chatting/handler/ChatVoiceHandler.java

@@ -7,21 +7,27 @@
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.mzc.secondproject.serverless.chatting.dto.ApiResponse;
+import com.mzc.secondproject.serverless.chatting.model.ChatMessage;
+import com.mzc.secondproject.serverless.chatting.repository.ChatMessageRepository;
 import com.mzc.secondproject.serverless.chatting.service.PollyService;
+import com.mzc.secondproject.serverless.chatting.service.PollyService.VoiceSynthesisResult;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.util.Map;
+import java.util.Optional;
 
 public class ChatVoiceHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
 
     private static final Logger logger = LoggerFactory.getLogger(ChatVoiceHandler.class);
     private static final Gson gson = new GsonBuilder().setPrettyPrinting().create();
 
     private final PollyService pollyService;
+    private final ChatMessageRepository messageRepository;
 
     public ChatVoiceHandler() {
         this.pollyService = new PollyService();
+        this.messageRepository = new ChatMessageRepository();
     }
 
     @Override
@@ -35,16 +41,61 @@ public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent re
 
             String body = request.getBody();
             Map<String, String> requestBody = gson.fromJson(body, Map.class);
-            String text = requestBody.get("text");
+            String messageId = requestBody.get("messageId");
+            String roomId = requestBody.get("roomId");
             String voice = requestBody.getOrDefault("voice", "FEMALE");
 
-            if (text == null || text.isEmpty()) {
-                return createResponse(400, ApiResponse.error("text is required"));
+            if (messageId == null || messageId.isEmpty()) {
+                return createResponse(400, ApiResponse.error("messageId is required"));
             }
+            if (roomId == null || roomId.isEmpty()) {
+                return createResponse(400, ApiResponse.error("roomId is required"));
+            }
+
+            // 메시지 조회
+            Optional<ChatMessage> messageOpt = messageRepository.findByRoomIdAndMessageId(roomId, messageId);
+            if (messageOpt.isEmpty()) {
+                return createResponse(404, ApiResponse.error("Message not found"));
+            }
+
+            ChatMessage message = messageOpt.get();
+            boolean isMale = "MALE".equalsIgnoreCase(voice);
+
+            // 캐시된 음성 키 확인
+            String cachedKey = isMale ? message.getMaleVoiceKey() : message.getFemaleVoiceKey();
 
-            String audioUrl = pollyService.synthesizeSpeech(text, voice);
+            String audioUrl;
+            boolean cached;
+
+            if (cachedKey != null && !cachedKey.isEmpty()) {
+                // 캐시 히트: DynamoDB에 키가 있으면 S3에서 URL 생성
+                logger.info("DB cache hit for message: {}, voice: {}", messageId, voice);
+                audioUrl = pollyService.getPresignedUrl(cachedKey);
+                cached = true;
+            } else {
+                // 캐시 미스: Polly 변환 → S3 저장 → DynamoDB 업데이트
+                VoiceSynthesisResult result = pollyService.synthesizeSpeechForMessage(
+                        messageId, message.getContent(), voice);
+
+                // DynamoDB에 S3 키 저장
+                if (isMale) {
+                    message.setMaleVoiceKey(result.getS3Key());
+                } else {
+                    message.setFemaleVoiceKey(result.getS3Key());
+                }
+                messageRepository.save(message);
+
+                audioUrl = result.getAudioUrl();
+                cached = result.isCached();
+            }
 
-            return createResponse(200, ApiResponse.success("Speech synthesized", Map.of("audioUrl", audioUrl)));
+            return createResponse(200, ApiResponse.success(
+                    cached ? "Speech retrieved from cache" : "Speech synthesized",
+                    Map.of(
+                            "audioUrl", audioUrl,
+                            "cached", cached
+                    )
+            ));
 
         } catch (Exception e) {
             logger.error("Error synthesizing speech", e);

chatting/ChatFunction/src/main/java/com/mzc/secondproject/serverless/chatting/model/ChatMessage.java

@@ -22,6 +22,8 @@ public class ChatMessage {
     private String sk;          // MSG#{timestamp}#{messageId}
     private String gsi1pk;      // USER#{userId}
     private String gsi1sk;      // MSG#{timestamp}
+    private String gsi2pk;      // MSG#{messageId} - messageId로 직접 조회용
+    private String gsi2sk;      // ROOM#{roomId}
 
     private String messageId;
     private String roomId;
@@ -31,6 +33,10 @@ public class ChatMessage {
     private String createdAt;
     private Long ttl;
 
+    // 음성 캐시용 S3 키 (voice/{messageId}_{voice}.mp3)
+    private String maleVoiceKey;
+    private String femaleVoiceKey;
+
     @DynamoDbPartitionKey
     @DynamoDbAttribute("PK")
     public String getPk() {
@@ -54,4 +60,16 @@ public String getGsi1pk() {
     public String getGsi1sk() {
         return gsi1sk;
     }
+
+    @DynamoDbSecondaryPartitionKey(indexNames = "GSI2")
+    @DynamoDbAttribute("GSI2PK")
+    public String getGsi2pk() {
+        return gsi2pk;
+    }
+
+    @DynamoDbSecondarySortKey(indexNames = "GSI2")
+    @DynamoDbAttribute("GSI2SK")
+    public String getGsi2sk() {
+        return gsi2sk;
+    }
 }

chatting/ChatFunction/src/main/java/com/mzc/secondproject/serverless/chatting/repository/ChatMessageRepository.java

@@ -23,16 +23,16 @@ public class ChatMessageRepository {
 
     private static final Logger logger = LoggerFactory.getLogger(ChatMessageRepository.class);
 
-    private final DynamoDbEnhancedClient enhancedClient;
+    // Singleton 패턴으로 Cold Start 최적화
+    private static final DynamoDbClient dynamoDbClient = DynamoDbClient.builder().build();
+    private static final DynamoDbEnhancedClient enhancedClient = DynamoDbEnhancedClient.builder()
+            .dynamoDbClient(dynamoDbClient)
+            .build();
+    private static final String tableName = System.getenv("CHAT_TABLE_NAME");
+
     private final DynamoDbTable<ChatMessage> table;
 
     public ChatMessageRepository() {
-        DynamoDbClient dynamoDbClient = DynamoDbClient.builder().build();
-        this.enhancedClient = DynamoDbEnhancedClient.builder()
-                .dynamoDbClient(dynamoDbClient)
-                .build();
-
-        String tableName = System.getenv("CHAT_TABLE_NAME");
         this.table = enhancedClient.table(tableName, TableSchema.fromBean(ChatMessage.class));
     }
 
@@ -43,13 +43,18 @@ public ChatMessage save(ChatMessage message) {
     }
 
     public Optional<ChatMessage> findByRoomIdAndMessageId(String roomId, String messageId) {
-        Key key = Key.builder()
-                .partitionValue("ROOM#" + roomId)
-                .sortValue("MSG#" + messageId)
-                .build();
+        // GSI2를 사용하여 messageId로 직접 조회 (풀스캔 방지)
+        QueryConditional queryConditional = QueryConditional
+                .keyEqualTo(Key.builder()
+                        .partitionValue("MSG#" + messageId)
+                        .sortValue("ROOM#" + roomId)
+                        .build());
 
-        ChatMessage message = table.getItem(key);
-        return Optional.ofNullable(message);
+        return table.index("GSI2")
+                .query(queryConditional)
+                .stream()
+                .flatMap(page -> page.items().stream())
+                .findFirst();
     }
 
     /**
@@ -127,20 +132,32 @@ private Map<String, AttributeValue> decodeCursor(String cursor) {
         }
     }
 
-    public List<ChatMessage> findByUserId(String userId) {
+    /**
+     * 사용자별 메시지 조회 - 페이지네이션 지원 (OOM 방지)
+     */
+    public MessagePage findByUserIdWithPagination(String userId, int limit, String cursor) {
         QueryConditional queryConditional = QueryConditional
                 .keyEqualTo(Key.builder().partitionValue("USER#" + userId).build());
 
-        QueryEnhancedRequest request = QueryEnhancedRequest.builder()
+        QueryEnhancedRequest.Builder requestBuilder = QueryEnhancedRequest.builder()
                 .queryConditional(queryConditional)
                 .scanIndexForward(false)  // 최신순
-                .build();
+                .limit(limit);
 
-        return table.index("GSI1")
-                .query(request)
-                .stream()
-                .flatMap(page -> page.items().stream())
-                .toList();
+        if (cursor != null && !cursor.isEmpty()) {
+            Map<String, AttributeValue> exclusiveStartKey = decodeCursor(cursor);
+            if (exclusiveStartKey != null) {
+                requestBuilder.exclusiveStartKey(exclusiveStartKey);
+            }
+        }
+
+        Page<ChatMessage> page = table.index("GSI1")
+                .query(requestBuilder.build())
+                .iterator()
+                .next();
+
+        String nextCursor = encodeCursor(page.lastEvaluatedKey());
+        return new MessagePage(page.items(), nextCursor);
     }
 
     /**

chatting/ChatFunction/src/main/java/com/mzc/secondproject/serverless/chatting/repository/ChatRoomRepository.java

@@ -13,6 +13,7 @@
 import software.amazon.awssdk.enhanced.dynamodb.model.QueryEnhancedRequest;
 import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
 import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
+import software.amazon.awssdk.services.dynamodb.model.UpdateItemRequest;
 
 import java.util.Base64;
 import java.util.HashMap;
@@ -24,16 +25,16 @@ public class ChatRoomRepository {
 
     private static final Logger logger = LoggerFactory.getLogger(ChatRoomRepository.class);
 
-    private final DynamoDbEnhancedClient enhancedClient;
+    // Singleton 패턴으로 Cold Start 최적화
+    private static final DynamoDbClient dynamoDbClient = DynamoDbClient.builder().build();
+    private static final DynamoDbEnhancedClient enhancedClient = DynamoDbEnhancedClient.builder()
+            .dynamoDbClient(dynamoDbClient)
+            .build();
+    private static final String tableName = System.getenv("CHAT_TABLE_NAME");
+
     private final DynamoDbTable<ChatRoom> table;
 
     public ChatRoomRepository() {
-        DynamoDbClient dynamoDbClient = DynamoDbClient.builder().build();
-        this.enhancedClient = DynamoDbEnhancedClient.builder()
-                .dynamoDbClient(dynamoDbClient)
-                .build();
-
-        String tableName = System.getenv("CHAT_TABLE_NAME");
         this.table = enhancedClient.table(tableName, TableSchema.fromBean(ChatRoom.class));
     }
 
@@ -166,6 +167,28 @@ public void delete(String roomId) {
         logger.info("Deleted room: {}", roomId);
     }
 
+    /**
+     * 채팅방 lastMessageAt 업데이트 (N+1 방지 - UpdateExpression 사용)
+     */
+    public void updateLastMessageAt(String roomId, String timestamp) {
+        Map<String, AttributeValue> key = new HashMap<>();
+        key.put("PK", AttributeValue.builder().s("ROOM#" + roomId).build());
+        key.put("SK", AttributeValue.builder().s("METADATA").build());
+
+        Map<String, AttributeValue> expressionValues = new HashMap<>();
+        expressionValues.put(":ts", AttributeValue.builder().s(timestamp).build());
+
+        UpdateItemRequest updateRequest = UpdateItemRequest.builder()
+                .tableName(tableName)
+                .key(key)
+                .updateExpression("SET lastMessageAt = :ts")
+                .expressionAttributeValues(expressionValues)
+                .build();
+
+        dynamoDbClient.updateItem(updateRequest);
+        logger.info("Updated lastMessageAt for room: {}", roomId);
+    }
+
     /**
      * 페이지네이션 결과 클래스
      */

chatting/ChatFunction/src/main/java/com/mzc/secondproject/serverless/chatting/service/ChatMessageService.java

@@ -33,8 +33,8 @@ public ChatMessageRepository.MessagePage getMessagesByRoomWithPagination(String
         return repository.findByRoomIdWithPagination(roomId, limit, cursor);
     }
 
-    public List<ChatMessage> getMessagesByUser(String userId) {
-        logger.info("Getting messages for user: {}", userId);
-        return repository.findByUserId(userId);
+    public ChatMessageRepository.MessagePage getMessagesByUserWithPagination(String userId, int limit, String cursor) {
+        logger.info("Getting messages for user: {} with limit: {}", userId, limit);
+        return repository.findByUserIdWithPagination(userId, limit, cursor);
     }
 }