fix: Gson → Kotlin Serialization 전환 및 kotlin.Result ProGuard 규칙 추가

1. ResponseInterceptor, ResultCall, FlowCallAdapter에서 Gson → kotlinx.serialization.json 전환
   - BaseResponse/ErrorResponse를 Gson으로 파싱하면 R8 난독화 시 필드명 매핑 실패
   - Kotlin Serialization은 컴파일 타임 코드 생성으로 난독화 영향 없음

2. kotlin.Result ProGuard 규칙 추가
   - R8이 inline class인 kotlin.Result의 제네릭 Signature를 최적화하면서
     Retrofit CallAdapter 생성 실패 (IllegalArgumentException)
   - square/retrofit#3880

3. DTO 필드 보존 규칙 제거
   - Gson 직접 사용이 없어져서 불필요

Author: unam98

app/proguard-rules.pro

@@ -11,14 +11,9 @@
 -keepattributes SourceFile,LineNumberTable
 -keep public class * extends java.lang.Exception
 
-# --- DTO ---
-# Gson 리플렉션으로 역직렬화되는 DTO 클래스의 필드명 보존
-# (BaseResponse, ErrorResponse 등이 Gson과 Kotlin Serialization 양쪽에서 사용됨)
--keepclassmembers class com.runnect.runnect.data.dto.** { <fields>; }
-
 # --- Retrofit + kotlin.Result ---
-# Retrofit이 리턴 타입의 제네릭 정보를 리플렉션으로 읽으므로 Signature 유지 필요
-# kotlin.Result는 inline class라 R8이 타입 정보를 최적화할 수 있음
+# kotlin.Result는 inline class라 R8이 제네릭 타입 정보를 최적화함
+# Retrofit이 Call<Result<T>>의 타입 파라미터를 리플렉션으로 읽지 못해 CallAdapter 생성 실패
 # https://github.com/square/retrofit/issues/3880
 -keep class kotlin.Result { *; }
 -keepattributes Signature

app/src/main/java/com/runnect/runnect/data/network/calladapter/ResultCall.kt

@@ -1,8 +1,10 @@
 package com.runnect.runnect.data.network.calladapter
 
-import com.google.gson.Gson
-import com.runnect.runnect.data.dto.response.base.ErrorResponse
 import com.runnect.runnect.domain.common.RunnectException
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.int
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
 import retrofit2.Call
 import retrofit2.Callback
 import retrofit2.Response
@@ -11,7 +13,7 @@ import okio.Timeout
 
 class ResultCall<T>(private val call: Call<T>) : Call<Result<T>> {
 
-    private val gson = Gson()
+    private val json = Json { ignoreUnknownKeys = true }
 
     override fun execute(): Response<Result<T>> {
         throw UnsupportedOperationException("ResultCall doesn't support execute")
@@ -46,23 +48,17 @@ class ResultCall<T>(private val call: Call<T>) : Call<Result<T>> {
     }
 
     private fun parseErrorResponse(response: Response<*>): RunnectException {
-        val errorJson = response.errorBody()?.string()
+        val errorString = response.errorBody()?.string()
 
         return runCatching {
-            val errorBody = gson.fromJson(errorJson, ErrorResponse::class.java)
-            val message = errorBody?.run {
-                message ?: error ?: ERROR_MSG_COMMON
-            }
-
-            RunnectException(
-                code = errorBody.status,
-                message = message
-            )
+            val jsonObject = json.parseToJsonElement(errorString.orEmpty()).jsonObject
+            val status = jsonObject["status"]?.jsonPrimitive?.int ?: response.code()
+            val message = jsonObject["message"]?.jsonPrimitive?.content
+                ?: jsonObject["error"]?.jsonPrimitive?.content
+                ?: ERROR_MSG_COMMON
+            RunnectException(code = status, message = message)
         }.getOrElse {
-            RunnectException(
-                code = response.code(),
-                message = ERROR_MSG_COMMON
-            )
+            RunnectException(code = response.code(), message = ERROR_MSG_COMMON)
         }
     }
 

app/src/main/java/com/runnect/runnect/data/network/calladapter/flow/FlowCallAdapter.kt

@@ -1,11 +1,12 @@
 package com.runnect.runnect.data.network.calladapter.flow
 
-import com.google.gson.Gson
-import com.runnect.runnect.data.dto.response.base.ErrorResponse
 import com.runnect.runnect.domain.common.RunnectException
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.flow
 import kotlinx.coroutines.suspendCancellableCoroutine
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
 import retrofit2.Call
 import retrofit2.CallAdapter
 import retrofit2.Callback
@@ -18,7 +19,7 @@ class FlowCallAdapter<T>(
     private val responseType: Type
 ) : CallAdapter<T, Flow<Result<T>>> {
 
-    private val gson = Gson()
+    private val json = Json { ignoreUnknownKeys = true }
     override fun responseType() = responseType
 
     // Retrofit의 Call을 Result<>로 변환
@@ -58,15 +59,18 @@ class FlowCallAdapter<T>(
         } ?: Result.failure(nullBodyException)
     }
 
-    // Response에서 오류를 파싱하여 RunnectException 객체를 생성
     private fun parseErrorResponse(response: Response<*>): RunnectException {
         val errorBodyString = response.errorBody()?.string()
-        val errorResponse = errorBodyString?.let {
-            gson.fromJson(it, ErrorResponse::class.java)
-        }
 
-        val errorMessage = errorResponse?.message ?: errorResponse?.error ?: ERROR_MSG_COMMON
-        return RunnectException(response.code(), errorMessage)
+        return runCatching {
+            val jsonObject = json.parseToJsonElement(errorBodyString.orEmpty()).jsonObject
+            val message = jsonObject["message"]?.jsonPrimitive?.content
+                ?: jsonObject["error"]?.jsonPrimitive?.content
+                ?: ERROR_MSG_COMMON
+            RunnectException(response.code(), message)
+        }.getOrElse {
+            RunnectException(response.code(), ERROR_MSG_COMMON)
+        }
     }
 
     companion object {

app/src/main/java/com/runnect/runnect/data/network/interceptor/ResponseInterceptor.kt

@@ -1,11 +1,8 @@
 package com.runnect.runnect.data.network.interceptor
 
-import com.google.gson.Gson
-import com.google.gson.JsonElement
-import com.google.gson.JsonObject
-import com.google.gson.JsonParseException
-import com.google.gson.JsonSyntaxException
-import com.runnect.runnect.data.dto.response.base.BaseResponse
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.jsonObject
 import okhttp3.Interceptor
 import okhttp3.MediaType.Companion.toMediaTypeOrNull
 import okhttp3.Response
@@ -18,14 +15,14 @@ import timber.log.Timber
  */
 class ResponseInterceptor : Interceptor {
 
-    private val gson = Gson()
+    private val json = Json { ignoreUnknownKeys = true }
 
     override fun intercept(chain: Interceptor.Chain): Response {
         val originalResponse = chain.proceed(chain.request())
         if (!originalResponse.isSuccessful) return originalResponse
 
         val bodyString = originalResponse.peekBody(Long.MAX_VALUE).string()
-        val newResponseBodyString = jsonToBaseResponse(bodyString)?.let {
+        val newResponseBodyString = extractData(bodyString)?.let {
             it.toResponseBody("application/json".toMediaTypeOrNull())
         } ?: return originalResponse
 
@@ -42,26 +39,18 @@ class ResponseInterceptor : Interceptor {
             }
     }
 
-    private fun jsonToBaseResponse(body: String): String? {
+    private fun extractData(body: String): String? {
         return try {
-            val jsonElement: JsonElement = gson.fromJson(body, JsonElement::class.java)
-            if (!isBaseResponse(jsonElement.asJsonObject)) {
-                return null
-            }
-
-            val baseResponse = gson.fromJson(body, BaseResponse::class.java)
-            gson.toJson(baseResponse.data)
-        } catch (e: JsonSyntaxException) {
-            null // JSON 구문 분석 오류 발생 시 원래 형식을 반환
-        } catch (e: JsonParseException) {
-            null // JSON 파싱 오류 발생 시 원래 형식을 반환
+            val jsonObject = json.parseToJsonElement(body).jsonObject
+            if (!isBaseResponse(jsonObject)) return null
+            jsonObject["data"].toString()
         } catch (e: Exception) {
-            null // 기타 예외 발생 시 원래 형식을 반환
+            null
         }
     }
 
     private fun isBaseResponse(jsonObject: JsonObject): Boolean {
         val requiredFields = listOf("status", "success", "message", "data")
-        return requiredFields.all { jsonObject.has(it) }
+        return requiredFields.all { it in jsonObject }
     }
 }