Simplify generic types; handle no content response

src/main/kotlin/com/haroldadmin/cnradapter/NetworkResponse.kt

@@ -24,7 +24,13 @@ import java.io.IOException
  * - Internet connectivity problems, the [NetworkResponse] is [NetworkResponse.NetworkError]
  * - Any other problems (e.g. Serialization errors), the [NetworkResponse] is [NetworkResponse.UnknownError].
  */
-public sealed interface NetworkResponse<S, E> {
+public sealed interface NetworkResponse<out S, out E> {
+
+    public sealed interface Success<S> : NetworkResponse<S, Nothing> {
+        public val body: S
+        public val response: Response<*>
+    }
+
     /**
      * The result of a successful network request.
      *
@@ -35,10 +41,43 @@ public sealed interface NetworkResponse<S, E> {
      * @param body The parsed body of the successful response.
      * @param response The original [Response] from Retrofit
      */
-    public data class Success<S, E>(
-        public val body: S,
-        public val response: Response<*>
-    ) : NetworkResponse<S, E> {
+    public data class OK<S>(
+        public override val body: S,
+        public override val response: Response<*>
+    ) : Success<S> {
+        /**
+         * The status code returned by the server.
+         *
+         * Alias for [Response.code] of the original response
+         */
+        public val code: Int
+            get() = response.code()
+
+        /**
+         * The headers returned by the server.
+         *
+         * Alias for [Response.headers] of the original response
+         */
+        public val headers: Headers
+            get() = response.headers()
+    }
+
+    /**
+     * The result of a successful network request.
+     *
+     * If you expect your server response to not contain a body, set the success body type ([S]) to [Unit].
+     * If you expect your server response to sometimes not contain a body (e.g. for response code 204), set
+     * [S] to [Unit] and deserialize the raw [response] manually when needed.
+     *
+     * @param response The original [Response] from Retrofit
+     */
+    public data class NoContent(
+        public override val response: Response<*>
+    ) : Success<Nothing> {
+
+        override val body: Nothing
+            get() = throw UnsupportedOperationException("Attempted to obtain body from no content response.")
+
         /**
          * The status code returned by the server.
          *
@@ -63,7 +102,7 @@ public sealed interface NetworkResponse<S, E> {
      * body ([ServerError]), or due to a connectivity error ([NetworkError]), or due to an unknown
      * error ([UnknownError]).
      */
-    public sealed interface Error<S, E> : NetworkResponse<S, E> {
+    public sealed interface Error<out E> : NetworkResponse<Nothing, E> {
         /**
          * The body of the failed network request, if available.
          */
@@ -81,10 +120,10 @@ public sealed interface NetworkResponse<S, E> {
      * This result may or may not contain a [body], depending on the body
      * supplied by the server.
      */
-    public data class ServerError<S, E>(
+    public data class ServerError<E>(
         public override val body: E?,
         public val response: Response<*>?,
-    ) : Error<S, E> {
+    ) : Error<E> {
         /**
          * The status code returned by the server.
          *
@@ -108,28 +147,29 @@ public sealed interface NetworkResponse<S, E> {
     /**
      * The result of a network connectivity error
      */
-    public data class NetworkError<S, E>(
+    public data class NetworkError(
         public override val error: IOException,
-    ) : Error<S, E> {
+    ) : Error<Nothing> {
 
         /**
          * Always `null` for a [NetworkError]
          */
-        override val body: E? = null
+        override val body: Nothing? = null
     }
 
     /**
      * Result of an unknown error during a network request
      * (e.g. Serialization errors)
      */
-    public data class UnknownError<S, E>(
+    public data class UnknownError(
         public override val error: Throwable,
         public val response: Response<*>?
-    ) : Error<S, E> {
+    ) : Error<Nothing> {
+
         /**
          * Always `null` for an [UnknownError]
          */
-        override val body: E? = null
+        override val body: Nothing? = null
 
         /**
          * The status code returned by the server.
@@ -152,4 +192,4 @@ public sealed interface NetworkResponse<S, E> {
  *
  * Useful for specifying return types of API calls that do not return a useful value.
  */
-public typealias CompletableResponse<E> = NetworkResponse<Unit, E>
+public typealias CompletableResponse<E> = NetworkResponse<Nothing, E>

src/main/kotlin/com/haroldadmin/cnradapter/ResponseParser.kt

@@ -21,7 +21,7 @@ internal fun <S, E> Response<S>.asNetworkResponse(
     return if (!isSuccessful) {
         parseUnsuccessfulResponse(this, errorConverter)
     } else {
-        parseSuccessfulResponse(this, successType)
+        parseSuccessfulResponse(this)
     }
 }
 
@@ -41,8 +41,9 @@ internal fun <S, E> Response<S>.asNetworkResponse(
 private fun <S, E> parseUnsuccessfulResponse(
     response: Response<S>,
     errorConverter: Converter<ResponseBody, E>
-): NetworkResponse.Error<S, E> {
-    val errorBody: ResponseBody = response.errorBody() ?: return NetworkResponse.ServerError(null, response)
+): NetworkResponse.Error<E> {
+    val errorBody: ResponseBody =
+        response.errorBody() ?: return NetworkResponse.ServerError(null, response)
 
     return try {
         val convertedBody = errorConverter.convert(errorBody)
@@ -62,18 +63,14 @@ private fun <S, E> parseUnsuccessfulResponse(
  *      - Else return a [NetworkResponse.ServerError] with a null body
  * - If response body is not null, return [NetworkResponse.Success] with the parsed body
  */
-private fun <S, E> parseSuccessfulResponse(response: Response<S>, successType: Type): NetworkResponse<S, E> {
-    val responseBody: S? = response.body()
-    if (responseBody == null) {
-        if (successType === Unit::class.java) {
-            @Suppress("UNCHECKED_CAST")
-            return NetworkResponse.Success<Unit, E>(Unit, response) as NetworkResponse<S, E>
+private fun <S, E> parseSuccessfulResponse(response: Response<S>): NetworkResponse<S, E> {
+    return when (val responseBody: S? = response.body()) {
+        null -> when (response.code()) {
+            204 -> NetworkResponse.NoContent(response)
+            else -> NetworkResponse.ServerError(null, response)
         }
-
-        return NetworkResponse.ServerError(null, response)
+        else -> NetworkResponse.OK(responseBody, response)
     }
-
-    return NetworkResponse.Success(responseBody, response)
 }
 
 /**

src/test/kotlin/com/haroldadmin/cnradapter/DeferredNetworkResponseAdapterTest.kt

@@ -13,12 +13,13 @@ import okhttp3.OkHttpClient
 import okhttp3.mockwebserver.MockResponse
 import okhttp3.mockwebserver.MockWebServer
 import okhttp3.mockwebserver.SocketPolicy
-import retrofit2.*
+import retrofit2.CallAdapter
+import retrofit2.Retrofit
 import retrofit2.http.GET
 import java.io.IOException
 import java.time.Duration
 
-class DeferredNetworkResponseAdapterTest : DescribeSpec({
+public class DeferredNetworkResponseAdapterTest : DescribeSpec({
     describe(DeferredNetworkResponseAdapter::class.java.simpleName) {
         it("should return success type correctly") {
             val converterFactory = StringConverterFactory()
@@ -90,7 +91,7 @@ class DeferredNetworkResponseAdapterTest : DescribeSpec({
             )
 
             val response = service.getTextAsync().await()
-            response.shouldBeInstanceOf<NetworkResponse.Success<String, String>>()
+            response.shouldBeInstanceOf<NetworkResponse.Success<String>>()
             response.body shouldBe "Test Message"
         }
 
@@ -103,20 +104,19 @@ class DeferredNetworkResponseAdapterTest : DescribeSpec({
             )
 
             val response = service.getTextAsync().await()
-            response.shouldBeInstanceOf<NetworkResponse.ServerError<String, String>>()
+            response.shouldBeInstanceOf<NetworkResponse.ServerError<String>>()
             response.body shouldBe "Not Found"
         }
 
         it("should handle 200 (with body) and 204 (no body) responses correctly") {
             server.enqueue(MockResponse().setBody("Test Message").setResponseCode(200))
             val response = service.getTextAsync().await()
-            response.shouldBeInstanceOf<NetworkResponse.Success<String, String>>()
+            response.shouldBeInstanceOf<NetworkResponse.OK<String>>()
             response.body shouldBe "Test Message"
 
             server.enqueue(MockResponse().setResponseCode(204))
             val noBodyResponse = service.getTextAsync().await()
-            noBodyResponse.shouldBeInstanceOf<NetworkResponse.ServerError<String, String>>()
-            noBodyResponse.body shouldBe null
+            noBodyResponse.shouldBeInstanceOf<NetworkResponse.NoContent>()
         }
 
         it("should return network error response as NetworkResponse.NetworkError") {
@@ -125,7 +125,7 @@ class DeferredNetworkResponseAdapterTest : DescribeSpec({
             )
 
             val response = service.getTextAsync().await()
-            response.shouldBeInstanceOf<NetworkResponse.NetworkError<String, String>>()
+            response.shouldBeInstanceOf<NetworkResponse.NetworkError>()
             response.error.shouldBeInstanceOf<IOException>()
         }
     }

src/test/kotlin/com/haroldadmin/cnradapter/ExtensionsTest.kt

@@ -15,28 +15,28 @@ import retrofit2.http.GET
 import java.io.IOException
 import java.time.Duration
 
-class ExtensionsTest : DescribeSpec({
+public class ExtensionsTest : DescribeSpec({
     context("Overloaded Invoke Operator") {
         it("should return the underlying body for NetworkResponse.Success") {
-            val response = NetworkResponse.Success<String, String>("Test Message", Response.success("Test Message"))
+            val response = NetworkResponse.OK("Test Message", Response.success("Test Message"))
             val body = response()
             body shouldBe "Test Message"
         }
 
         it("should return null for NetworkResponse.ServerError") {
-            val response = NetworkResponse.ServerError<String, String>(null, null)
+            val response = NetworkResponse.ServerError(null, null)
             val body = response()
             body shouldBe null
         }
 
         it("should return null for NetworkResponse.NetworkError") {
-            val response = NetworkResponse.NetworkError<String, String>(IOException())
+            val response = NetworkResponse.NetworkError(IOException())
             val body = response()
             body shouldBe null
         }
 
         it("should return null for NetworkResponse.UnknownError") {
-            val response = NetworkResponse.UnknownError<String, String>(Exception(), null)
+            val response = NetworkResponse.UnknownError(Exception(), null)
             val body = response()
             body shouldBe null
         }
@@ -77,7 +77,7 @@ class ExtensionsTest : DescribeSpec({
                 service.getTextAsync().await()
             }
 
-            response.shouldBeInstanceOf<NetworkResponse.Success<String, String>>()
+            response.shouldBeInstanceOf<NetworkResponse.Success<String>>()
             response.body shouldBe "Hi!"
         }
 
@@ -92,7 +92,7 @@ class ExtensionsTest : DescribeSpec({
                 service.getText()
             }
 
-            response.shouldBeInstanceOf<NetworkResponse.Success<String, String>>()
+            response.shouldBeInstanceOf<NetworkResponse.Success<String>>()
             response.body shouldBe "Hi!"
         }
     }