skydoves/sandwich

Why Sandwich?

Sandwich was conceived to streamline the creation of standardized interfaces to model responses from Retrofit, Ktor, and whatever. This library empowers you to handle body data, errors, and exceptional cases more succinctly, utilizing functional operators within a multi-layer architecture. With Sandwich, the need to create wrapper classes like Resource or Result is eliminated, allowing you to concentrate on your core business logic. Sandwich boasts features such as global response handling, Mapper, Operator, and exceptional compatibility, including ApiResponse With Coroutines.

Download

Sandwich has achieved an impressive milestone, being downloaded in over 1,200,000 across Android and backend projects worldwide!

Gradle

Add the dependency below into your module's build.gradle file:

dependencies {
    implementation("com.github.skydoves:sandwich:2.3.0")
    implementation("com.github.skydoves:sandwich-retrofit:2.3.0") // For Retrofit (Android)
    testImplementation("com.github.skydoves:sandwich-test:2.3.0") // For Testing
}

For Kotlin Multiplatform, add the dependency below to your module's build.gradle.kts file:

sourceSets {
    val commonMain by getting {
        dependencies {
            implementation("com.github.skydoves:sandwich:$version")
            implementation("com.github.skydoves:sandwich-ktor:$version")
            implementation("com.github.skydoves:sandwich-ktorfit:$version")
        }
    }
    val commonTest by getting {
        dependencies {
            implementation("com.github.skydoves:sandwich-test:$version")
        }
    }
}

R8 / ProGuard

The specific rules are already bundled into the JAR which can be interpreted by R8 automatically.

Documentation

For comprehensive details about Sandwich, please refer to the complete documentation available here.

Use Cases

You can also check out nice use cases of this library in the repositories below:

• Pokedex: 🗡️ Android Pokedex using Hilt, Motion, Coroutines, Flow, Jetpack (Room, ViewModel, LiveData) based on MVVM architecture.
• ChatGPT Android: 📲 ChatGPT Android demonstrates OpenAI's ChatGPT on Android with Stream Chat SDK for Compose.
• DisneyMotions: 🦁 A Disney app using transformation motions based on MVVM (ViewModel, Coroutines, LiveData, Room, Repository, Koin) architecture.
• MarvelHeroes: ❤️ A sample Marvel heroes application based on MVVM (ViewModel, Coroutines, LiveData, Room, Repository, Koin) architecture.
• Neko: Free, open source, unofficial MangaDex reader for Android.
• TheMovies2: 🎬 A demo project using The Movie DB based on Kotlin MVVM architecture and material design & animations.

Usage

For comprehensive details about Sandwich, please refer to the complete documentation available here.

• Retrofit Integration
• Ktor Integration
• Ktorfit Integration
• Testing

ApiResponse

ApiResponse serves as an interface designed to create consistent responses from API or I/O calls, such as network, database, or whatever. It offers convenient extensions to manage your payloads, encompassing both body data and exceptional scenarios. ApiResponse encompasses three distinct types: Success, Failure.Error, and Failure.Exception.

ApiResponse.Success

This represents a successful response from API or I/O tasks. You can create an instance of [ApiResponse.Success] by giving the generic type and data.

val apiResponse = ApiResponse.Success(data = myData)
val data = apiResponse.data

Depending on your model designs, you can also utilize tag property. The tag is an additional value that can be held to distinguish the origin of the data or to facilitate post-processing of successful data.

val apiResponse = ApiResponse.Success(data = myData, tag = myTag)
val tag = apiResponse.tag

ApiResponse.Failure.Exception

This signals a failed tasks captured by unexpected exceptions during API request creation or response processing on the client side, such as a network connection failure. You can obtain exception details from the ApiResponse.Failure.Exception.

val apiResponse = ApiResponse.Failure.Exception(exception = HttpTimeoutException())
val exception = apiResponse.exception
val message = apiResponse.message

ApiResponse.Failure.Error

This denotes a failed API or I/O request, typically due to bad requests or internal server errors. You can additionally put an error payload that can contain detailed error information.

val apiResponse = ApiResponse.Failure.Error(payload = errorBody)
val payload = apiResponse.payload

You can also define custom error responses that extend ApiResponse.Failure.Error or ApiResponse.Failure.Exception, as demonstrated in the example below:

data object LimitedRequest : ApiResponse.Failure.Error(
  payload = "your request is limited",
)

data object WrongArgument : ApiResponse.Failure.Error(
  payload = "wrong argument",
)

data object HttpException : ApiResponse.Failure.Exception(
  throwable = RuntimeException("http exception")
)

The custom error response is very useful when you want to explicitly define and handle error responses, especially when working with map extensions.

val apiResponse = service.fetchMovieList()
apiResponse.onSuccess {
    // ..
}.flatMap {
  // if the ApiResponse is Failure.Error and contains error body, then maps it to a custom error response.  
  if (this is ApiResponse.Failure.Error) {
    val errorBody = (payload as? Response)?.body?.string()
    if (errorBody != null) {
      val errorMessage: ErrorMessage = Json.decodeFromString(errorBody)
      when (errorMessage.code) {
        10000 -> LimitedRequest
        10001 -> WrongArgument
      }
    }
  }
  this
}

Then you can handle the errors based on your custom message in other layers:

val apiResponse = repository.fetchMovieList()
apiResponse.onError {
  when (this) {
    LimitedRequest -> // update your UI
    WrongArgument -> // update your UI
  }
}

You might not want to use the flatMap extension for all API requests. If you aim to standardize custom error types across all API requests, you can explore the Global Failure Mapper.

Creation of ApiResponse

Sandwich provides convenient ways to create an ApiResponse using functions such as ApiResponse.of or apiResponseOf, as shown below:

val apiResponse = ApiResponse.of { service.request() }
val apiResponse = apiResponseOf { service.request() }

If you need to run suspend functions inside the lambda, you can use ApiResponse.suspendOf or suspendApiResponseOf instead:

val apiResponse = ApiResponse.suspendOf { service.request() }
val apiResponse = suspendApiResponseOf { service.request() }

Note: If you intend to utilize the global operator or global ApiResponse mapper in Sandwich, you should create an ApiResponse using the ApiResponse.of or ApiResponse.suspendOf method to ensure the application of these global functions. If you're using ApiResponseFailureSuspendMapper or ApiResponseSuspendOperator (common with Ktor/Ktorfit), use ApiResponse.suspendOf to ensure suspend mappers and operators are properly awaited.

ApiResponse Extensions

You can effectively handle ApiResponse using the following extensions:

• onSuccess: Executes when the ApiResponse is of type ApiResponse.Success. Within this scope, you can directly access the body data.
• onError: Executes when the ApiResponse is of type ApiResponse.Failure.Error. You can access messageOrNull and payload here.
• onException: Executes when the ApiResponse is of type ApiResponse.Failure.Exception. You can access messageOrNull and exception here.
• onFailure: Executes when the ApiResponse is either ApiResponse.Failure.Error or ApiResponse.Failure.Exception. You can access messageOrNull here.

Each scope operates according to its corresponding ApiResponse type:

val response = disneyService.fetchDisneyPosterList()
response.onSuccess {
    // this scope will be executed if the request successful.
    // handle the success case
  }.onError {
    // this scope will be executed when the request failed with errors.
    // handle the error case
  }.onException {
   // this scope will be executed when the request failed with exceptions.
   // handle the exception case
  }

If you don't want to specify each failure case, you can simplify it by using the onFailure extension:

val response = disneyService.fetchDisneyPosterList()
response.onSuccess {
    // this scope will be executed if the request successful.
    // handle the success case
  }.onFailure {

  }

ApiResponse Extensions With Coroutines

With the ApiResponse type, you can leverage Coroutines extensions to handle responses seamlessly within coroutine scopes. These extensions provide a convenient way to process different response types. Here's how you can use them:

• suspendOnSuccess: This extension runs if the ApiResponse is of type ApiResponse.Success. You can access the body data directly within this scope.

• suspendOnError: This extension is executed if the ApiResponse is of type ApiResponse.Failure.Error. You can access the error message and the error body in this scope.

• suspendOnException: If the ApiResponse is of type ApiResponse.Failure.Exception, this extension is triggered. You can access the exception message in this scope.

• suspendOnFailure: This extension is executed if the ApiResponse is either ApiResponse.Failure.Error or ApiResponse.Failure.Exception. You can access the error message in this scope.

Each extension scope operates based on the corresponding ApiResponse type. By utilizing these extensions, you can handle responses effectively within different coroutine contexts.

flow {
  val response = disneyService.fetchDisneyPosterList()
  response.suspendOnSuccess {
    posterDao.insertPosterList(data) // insertPosterList(data) is a suspend function.
    emit(data)
  }.suspendOnError {
    // handles error cases
  }.suspendOnException {
    // handles exceptional cases
  }
}.flowOn(Dispatchers.IO)

Flow

Sandwich offers some useful extensions to transform your ApiResponse into a Flow by using the toFlow extension:

val flow = disneyService.fetchDisneyPosterList()
  .onError {
    // handles error cases when the API request gets an error response.
  }.onException {
    // handles exceptional cases when the API request gets an exception response.
  }.toFlow() // returns a coroutines flow
  .flowOn(Dispatchers.IO)

If you want to transform the original data and work with a Flow containing the transformed data, you can do so as shown in the examples below:

val response = pokedexClient.fetchPokemonList(page = page)
response.toFlow { pokemons ->
  pokemons.forEach { pokemon -> pokemon.page = page }
  pokemonDao.insertPokemonList(pokemons)
  pokemonDao.getAllPokemonList(page)
}.flowOn(Dispatchers.IO)

Functional Extensions

Sandwich provides a variety of functional extensions for transforming and composing ApiResponse:

• Recovery: recover, recoverWith - Transform failures back into successes with fallback data
• Validation: validate, requireNotNull - Validate success data and convert it to failure if invalid
• Filter: filter, filterNot - Filter items in list data within a successful response
• Zip/Combine: zip, zip3 - Combine multiple ApiResponse instances into one
• Peek/Tap: peek, peekSuccess, peekFailure, peekError, peekException - Observe responses without modifying them

val response = disneyService.fetchDisneyPosterList()
  .validate({ it.isNotEmpty() }) { "List cannot be empty" }  // Validate data
  .filter { poster -> poster.isActive }                       // Filter list items
  .recover(emptyList()