entityCallback에서 호출하는 backfill 로직의 코루틴 컨텍스트를 Unconfined로 변경

api/src/main/kotlin/handler/DeviceHandler.kt

@@ -3,7 +3,6 @@ package com.wafflestudio.snu4t.handler
 import com.wafflestudio.snu4t.common.dto.OkResponse
 import com.wafflestudio.snu4t.middleware.SnuttRestApiDefaultMiddleware
 import com.wafflestudio.snu4t.notification.service.DeviceService
-import com.wafflestudio.snu4t.users.data.User
 import com.wafflestudio.snu4t.users.service.UserNicknameService
 import com.wafflestudio.snu4t.users.service.UserService
 import org.springframework.stereotype.Component

core/src/main/kotlin/users/data/UserEntityCallback.kt

@@ -1,28 +1,42 @@
 package com.wafflestudio.snu4t.users.data
 
-import com.wafflestudio.snu4t.users.service.UserNicknameBackFillSupporter
+import com.wafflestudio.snu4t.users.repository.UserRepository
+import com.wafflestudio.snu4t.users.service.UserNicknameService
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.reactor.mono
 import org.bson.Document
 import org.reactivestreams.Publisher
 import org.slf4j.LoggerFactory
 import org.springframework.context.annotation.Lazy
-import org.springframework.core.CoroutinesUtils
 import org.springframework.data.mongodb.core.mapping.event.ReactiveAfterConvertCallback
 import org.springframework.stereotype.Component
 import reactor.core.publisher.Mono
 
 @Component
-class UserEntityCallback(
-    @Lazy private val supporter: UserNicknameBackFillSupporter
+class UserEntityCallback @Lazy constructor(
+    private val userRepository: UserRepository,
+    private val userNicknameService: UserNicknameService,
 ) : ReactiveAfterConvertCallback<User> {
 
     private val log = LoggerFactory.getLogger(javaClass)
 
     override fun onAfterConvert(entity: User, document: Document, collection: String): Publisher<User> {
-        if (entity.nickname == null) {
-            log.info("empty nickname found. user: $entity")
-            return CoroutinesUtils.deferredToMono(supporter.backFillNickname(entity))
+        if (entity.nickname != null) {
+            return Mono.just(entity)
         }
 
-        return Mono.just(entity)
+        log.info("empty nickname found. user: $entity")
+        return backFillNickname(entity)
+    }
+
+    private fun backFillNickname(user: User): Mono<User> = mono(Dispatchers.Unconfined) {
+        try {
+            val result = userRepository.save(user.copy(nickname = userNicknameService.generateUniqueRandomNickname()))
+            log.info("[BACKFILL] updated nickname of USER: $result")
+            result
+        } catch (e: Exception) {
+            log.error("[BACKFILL] failed to update nickname of USER: $user", e)
+            throw e
+        }
     }
 }