v1.x.y

The easiest HTTP networking library for Kotlin/Android.

Features

• Support basic HTTP GET/POST/PUT/DELETE/HEAD/PATCH in a fluent style interface

• Support both asynchronous and blocking requests

• Download file

• Upload file (multipart/form-data)

• Cancel in-flight request

• Request timeout

• Configuration manager by using FuelManager

• Debug log / cUrl log

• Support response deserialization into plain old object (both Kotlin & Java)

• Automatically invoke handler on Android Main Thread when using Android Module

• Special test mode for easier testing

• Support for reactive programming via RxJava 2.x and Project Reactor 3.x

• Google Components LiveData support

• Built-in object serialization module (kotlinx-serialization, Gson, Jackson, Moshi, Forge) :sparkles:

• Support Kotlin's Coroutines module

• API Routing

Installation

There are 2 versions of Fuel build against different Kotlin Versions

• Kotlin - 1.2.71

• Coroutine - 0.23.3

• Kotlin - 1.3.0-rc-146

• Coroutine - 0.30.1-eap13

Dependency - fuel

• Result - The modelling for success/failure of operations in Kotlin

Dependency - fuel-android

• Android SDK - Android SDK

• Min SDK: 19

Dependency - fuel-livedata

• Live Data - Android Architecture Components - LiveData

Dependency - fuel-rxjava

• RxJava - RxJava – Reactive Extensions for the JVM

Dependency - fuel-coroutines

• Coroutines - Kotlin Coroutines - Library support for Kotlin coroutines

Dependency - fuel-kotlinx-serialization

• Kotlinx Serialization - Kotlinx Serialization - Kotlin cross-platform / multi-format serialization

Dependency - fuel-gson

• Gson - Gson - A Java serialization/deserialization library to convert Java Objects into JSON and back

Dependency - fuel-jackson

• Jackson - Jackson - The JSON library for Java

Dependency - fuel-moshi

• Moshi - Moshi - A modern JSON library for Android and Java

Dependency - fuel-forge

• Forge - Forge - Functional style JSON parsing written in Kotlin

Dependency - fuel-reactor

• Project Reactor - Project Reactor - Implementation of Reactive Streams standard

Gradle

repositories {
    jcenter()
}

dependencies {
    compile 'com.github.kittinunf.fuel:fuel:<latest-version>' //for JVM
    compile 'com.github.kittinunf.fuel:fuel-android:<latest-version>' //for Android
    compile 'com.github.kittinunf.fuel:fuel-livedata:<latest-version>' //for LiveData support
    compile 'com.github.kittinunf.fuel:fuel-rxjava:<latest-version>' //for RxJava support
    compile 'com.github.kittinunf.fuel:fuel-coroutines:<latest-version>' //for Kotlin Coroutines support
    compile 'com.github.kittinunf.fuel:fuel-gson:<latest-version>' //for Gson support
    compile 'com.github.kittinunf.fuel:fuel-jackson:<latest-version>' //for Jackson support
    compile 'com.github.kittinunf.fuel:fuel-moshi:<latest-version>' //for Moshi support
    compile 'com.github.kittinunf.fuel:fuel-forge:<latest-version>' //for Forge support
    compile 'com.github.kittinunf.fuel:fuel-reactor:<latest-version>' //for Reactor support
}

Sample

• There are two samples, one is in Kotlin and another one in Java.

Quick Glance Usage

Async mode

• Kotlin

  ```kotlin

  //an extension over string (support GET, PUT, POST, DELETE with httpGet(), httpPut(), httpPost(), httpDelete())

  "https://httpbin.org/get".httpGet().responseString { request, response, result ->

  //do something with response

  when (result) {

  is Result.Failure -> {

  val ex = result.getException()

  }

  is Result.Success -> {

  val data = result.get()

  }

  }

  }

//if we set baseURL beforehand, simply use relativePath FuelManager.instance.basePath = "https://httpbin.org" "/get".httpGet().responseString { request, response, result -> //make a GET to https://httpbin.org/get and do something with response val (data, error) = result if (error == null) { //do something when success } else { //error handling } }

//if you prefer this a little longer way, you can always do //get Fuel.get("https://httpbin.org/get").responseString { request, response, result -> //do something with response result.fold({ d -> //do something with data }, { err -> //do something with error }) }

* Java
```java
//get
Fuel.get("https://httpbin.org/get", params).responseString(new Handler<String>() {
    @Override
    public void failure(Request request, Response response, FuelError error) {
        //do something when it is failure
    }

    @Override
    public void success(Request request, Response response, String data) {
        //do something when it is successful
    }
});

Blocking mode

You can also wait for the response. It returns the same parameters as the async version, but it blocks the thread. It supports all the features of the async version.

• Kotlin

  val (request, response, result) = "https://httpbin.org/get".httpGet().responseString() // result is Result<String, FuelError>

• Java

  ```java try { Triple data = Fuel.get("https://www.google.com").responseString(); Request request = data.getFirst(); Response response = data.getSecond(); Result text = data.getThird(); } catch (Exception networkError) {

}

## Detail Usage

### GET

```kotlin
Fuel.get("https://httpbin.org/get").response { request, response, result ->
    println(request)
    println(response)
    val (bytes, error) = result
    if (bytes != null) {
        println(bytes)
    }
}

Response Handling

Result

• Result is a functional style data structure that represents data that contains result of Success or Failure but not both. It represents the result of an action that can be success (with result) or error.

• Working with result is easy. You could fold, destructure as because it is just a data class or do a simple when checking whether it is Success or Failure.

Response

fun response(handler: (Request, Response, Result<ByteArray, FuelError>) -> Unit)

Response in String

fun responseString(handler: (Request, Response, Result<String, FuelError>) -> Unit)

Response in Json

requires the android extension

fun responseJson(handler: (Request, Response, Result<Json, FuelError>) -> Unit)

val jsonObject = json.obj() //JSONObject
val jsonArray = json.array() //JSONArray

Response in T (object)

fun <T> responseObject(deserializer: ResponseDeserializable<T>, handler: (Request, Response, Result<T, FuelError>) -> Unit)

POST

Fuel.post("https://httpbin.org/post").response { request, response, result ->
}

// JSON body from string (automatically sets application/json as Content-Type)
Fuel.post("https://httpbin.org/post")
    .jsonBody("{ \"foo\" : \"bar\" }")
    .response { request, response, result -> }

// Body from a generic string
Fuel.post("https://httpbin.org/post")
    .header(Headers.CONTENT_TYPE, "text/plain")
    .body("my body is plain")
    .response { request, response, result -> }

// Body from a file
Fuel.post("https://httpbin.org/post")
    .header(Headers.CONTENT_TYPE, "text/plain")
    .body(File("lipsum.txt"))
    .response { request, response, result -> }

// Body from a generic stream
val stream = ByteArrayInputStream("source-string-from-string".toByteArray())
Fuel.post("https://httpbin.org/post")
    .header(Headers.CONTENT_TYPE, "text/plain")
    .body(stream)
    .response { request, response, result -> }

PUT

Fuel.put("https://httpbin.org/put")
    .response { request, response, result -> }

// Supports all the body methods, like POST requests

DELETE

Fuel.delete("https://httpbin.org/delete")
    .response { request, response, result -> }

// Supports all the body methods, like POST requests

HEAD

Fuel.head("https://httpbin.org/get")
    .response { request, response, result -> /* request body is empty */ }

PATCH

• The default client is HttpClient which is a thin wrapper over java.net.HttpUrlConnection. java.net.HttpUrlConnection does not support a [PATCH](https://download.java.net/jdk7/archive/b123/docs/api/java/net/HttpURLConnection.html#setRequestMethod(java.lang.String)) method. HttpClient converts PATCH requests to a POST request and adds a X-HTTP-Method-Override: PATCH header. While this is a semi-standard industry practice not all APIs are configured to accept this header by default.

Fuel.patch("https://httpbin.org/patch").response { request, response, result -> }

// Supports all the body methods, like POST requests

CONNECT

Connect is not supported by the Java JVM via the regular HTTP clients, and is therefore not supported.

OPTIONS

There are no convenience methods for making an OPTIONS request, but you can still make one directly:

Fuel.request(Method.OPTIONS, "https://httpbin.org/anything")
    .response { request, response, result -> }

TRACE

There are no convenience methods for making an TRACE request, but you can still make one directly:

Fuel.request(Method.TRACE, "https://httpbin.org/anything")
    .response { request, response, result -> }

Debug Logging

• Use toString() method to inspect requests

val request = Fuel.get("https://httpbin.org/get", parameters = listOf("key" to "value"))
println(request)

// --> GET (https://httpbin.org/get?key=value)
//    Body : (empty)
//    Headers : (2)
//    Accept-Encoding : compress;q=0.5, gzip;q=1.0
//    Device : Android

• Use toString() method to inspect responses

val (_, response, _) = Fuel.get("https://httpbin.org/get", parameters = listOf("key" to "value")).response()
println(response)
// <-- 200 (https://httpbin.org/get?key=value)
//    Body : (empty)

• Also support cUrl string to Log request, make it very easy to cUrl on command line

val request = Fuel.post("https://httpbin.org/post", parameters = listOf("foo" to "foo", "bar" to "bar", "key" to "value"))
println(request.cUrlString())

curl -i -X POST -d "foo=foo&bar=bar&key=value" -H "Accept-Encoding:compress;q=0.5, gzip;q=1.0" -H "Device:Android" -H "Content-Type:application/x-www-form-urlencoded" "https://httpbin.org/post"

Parameter Support

• URL encoded style for GET & DELETE request

Fuel.get("https://httpbin.org/get", listOf("foo" to "foo", "bar" to "bar"))
    .response { request, response, result -> }
// resolve to https://httpbin.org/get?foo=foo&bar=bar

Fuel.delete("https://httpbin.org/delete", listOf("foo" to "foo", "bar" to "bar"))
    .response { request, response, result -> }
// resolve to https://httpbin.org/delete?foo=foo&bar=bar

• Array support for GET requests

Fuel.get("https://httpbin.org/get", listOf("foo" to "foo", "dwarf" to  arrayOf("grumpy","happy","sleepy","dopey")))
    .response { request, response, result -> }
// resolve to  https://httpbin.org/get?foo=foo&dwarf[]=grumpy&dwarf[]=happy&dwarf[]=sleepy&dwarf[]=dopey

• Support x-www-form-urlencoded for PUT & POST

Fuel.post("https://httpbin.org/post", listOf("foo" to "foo", "bar" to "bar"))
    .response { request, response, result -> }
// Body : "foo=foo&bar=bar"

Fuel.put("https://httpbin.org/put", listOf("foo" to "foo", "bar" to "bar"))
    .response { request, response, result -> }
// Body : "foo=foo&bar=bar"

Set request's timeout and read timeout

Default timeout for a request is 15000 milliseconds. Default read timeout for a request is 15000 milliseconds.

• Kotlin

  ```kotlin

  val timeout = 5000 // 5000 milliseconds = 5 seconds.

  val timeoutRead = 60000 // 60000 milliseconds = 1 minute.

Fuel.get("https://httpbin.org/get") .timeout(timeout) .timeoutRead(timeoutRead) .responseString { request, response, result -> }

* Java
```java
int timeout = 5000 // 5000 milliseconds = 5 seconds.
int timeoutRead = 60000 // 60000 milliseconds = 1 minute.
Fuel.get("https://httpbin.org/get", params).timeout(timeout).timeoutRead(timeoutRead).responseString(new Handler<String>() {
    @Override
    public void failure(Request request, Response response, FuelError error) {
        //do something when it is failure
    }

    @Override
    public void success(Request request, Response response, String data) {
        //do something when it is successful
    }
});

Download with or without progress handler

Fuel.download("https://httpbin.org/bytes/32768")
    .destination { response, url -> File.createTempFile("temp", ".tmp") }
    .response { req, res, result -> }

Fuel.download("https://httpbin.org/bytes/32768")
    .destination { response, url -> File.createTempFile("temp", ".tmp") }
    .progress { readBytes, totalBytes ->
        val progress = readBytes.toFloat() / totalBytes.toFloat() * 100
        println("Bytes downloaded $readBytes / $totalBytes ($progress %)")
    }
    .response { req, res, result -> }

Upload with or without progress handler

Fuel.upload("/post")
    .source { request, url -> File.createTempFile("temp", ".tmp") }
    .responseString { request, response, result -> }

// By default upload use Method.POST, unless it is specified as something else
Fuel.upload("/put", Method.PUT)
    .source { request, url -> File.createTempFile("temp", ".tmp") }
    .responseString { request, response, result -> }

// Upload with multiple files
Fuel.upload("/post")
    .sources { request, url ->
        listOf(
            File.createTempFile("temp1", ".tmp"),
            File.createTempFile("temp2", ".tmp")
        )
    }
    .name { "temp" }
    .responseString { request, response, result -> }

Specify custom field names for files

Fuel.upload("/post")
    .dataParts { request, url -> 
        listOf( 
            //DataPart takes a file, and you can specify the name and/or type
            DataPart(File.createTempFile("temp1", ".tmp"), "image/jpeg"), 
            DataPart(File.createTempFile("temp2", ".tmp"), "file2"), 
            DataPart(File.createTempFile("temp3", ".tmp"), "third-file", "image/jpeg") 
        ) 
    }
    .responseString { request, response, result -> /* ... */ }

Upload a multipart form without a file

val formData = listOf("Email" to "[e-mail]", "Name" to "Joe Smith" )
Fuel.upload("/post", param = formData)
    // Upload normally requires a file, but we can give it an empty list of `DataPart`
    .dataParts { request, url -> listOf<DataPart>() } 
    .responseString { request, response, result -> /* ... */ }

Upload from an InputStream

Fuel.upload("/post")
    .blob { request, url -> Blob("filename.png", someObject.length) { someObject.getInputStream() } }

Authentication

• Support Basic Authentication right off the box

    val username = "username"
    val password = "abcd1234"
  
    Fuel.get("https://httpbin.org/basic-auth/$user/$password")
        .basicAuthentication(username, password)
        .response { request, response, result -> }

• Support Bearer Authentication

    val token = "mytoken"
  
    Fuel.get("https://httpbin.org/bearer")
        .bearerAuthentication(token)
        .response { request, response, result -> }

• Support Any authentication by header

    Fuel.get("https://httpbin.org/anything")
        .header(Headers.AUTHORIZATION, "Custom secret")
        .response { request, response, result -> }

Validation

• By default, the valid range for HTTP status code will be (200..299).

Cancel

• If one wants to cancel on-going request, one could call cancel on the request object

    val request = Fuel.get("https://httpbin.org/get")
      .response { request, response, result ->
        // if request is cancelled successfully, response callback will not be called. 
        // Interrupt callback (if provided) will be called instead
      }
  
    //later
    request.cancel() //this will cancel on-going request

• Also, interrupt request can be further processed with interrupt callback

    val request = Fuel.get("https://httpbin.org/get")
      .interrupt { request -> println("${request.url} was interrupted and cancelled") }
      .response { request, response, result ->
        // if request is cancelled successfully, response callback will not be called.
        // Interrupt callback (if provided) will be called instead
      }
  
    request.cancel()

Advanced Configuration

Response Deserialization

• Fuel provides built-in support for response deserialization. Here is how one might want to use Fuel together with Gson

  ```kotlin //User Model data class User(val firstName: String = "", val lastName: String = "") {

  //User Deserializer class Deserializer : ResponseDeserializable { override fun deserialize(content: String) = Gson().fromJson(content, User::class.java) }

}

//Use httpGet extension "https://www.example.com/user/1".httpGet().responseObject(User.Deserializer()) { req, res, result -> //result is of type Result val (user, err) = result

println(user.firstName)
println(user.lastName)

}

### Gson Deserialization

* Fuel also provides a built in support for Gson Deserialization. This is possible by including the [Gson](https://github.com/kittinunf/Fuel/tree/master/fuel-gson) module in your dependency block.

```kotlin
data class HttpBinUserAgentModel(var userAgent: String = "")
Fuel.get("/user-agent")
    .responseObject<HttpBinUserAgentModel> { _, _, result -> }

Deserialization using kotlinx.serialzationn

requires the kotlinx-serialization extension requires kotlinx.serialization

@Serializable
data class HttpBinUserAgentModel(var userAgent: String = "")

Fuel.get("/user-agent")
    .responseObject<HttpBinUserAgentModel> { _, _, result -> }

This is by default strict and will reject unknown keys, for that you can pass a custom JSOn instance

JSON(nonstrict = true)

@Serializable
data class HttpBinUserAgentModel(var userAgent: String = "")

Fuel.get("/user-agent")
    .responseObject<HttpBinUserAgentModel>(json = JSON(nonstrict = true)) { _, _, result -> }

kotlinx.serialization can not always guess the correct serialzer to use, when generics are involved for example

@Serializable
data class HttpBinUserAgentModel(var userAgent: String = "")

Fuel.get("/list/user-agent")
    .responseObject<HttpBinUserAgentModel>(loader = HttpBinUserAgentModel.serilaizer().list) { _, _, result -> }

It can be used with coroutines by using kotlinxDeserilaizerOf() it takes the same json and loader as parameters

@Serializable
data class HttpBinUserAgentModel(var userAgent: String = "")

Fuel.get("/user-agent")
    .awaitResponseObject<HttpBinUserAgentModel>(kotlinxDeserializerOf()) { _, _, result -> }

• There are 4 methods to support response deserialization depending on your needs (also depending on JSON parsing library of your choice), and you are required to implement only one of them.

    fun deserialize(bytes: ByteArray): T?
  
    fun deserialize(inputStream: InputStream): T?
  
    fun deserialize(reader: Reader): T?
  
    fun deserialize(content: String): T?

• Another example may be parsing a website that is not UTF-8. By default, Fuel serializes text as UTF-8, we need to define our deserializer as such

    object Windows1255StringDeserializer : ResponseDeserializable<String> {
        override fun deserialize(bytes: ByteArray): String {
            return String(bytes, "windows-1255")
        }
    }

Configuration

• Use singleton FuelManager.instance to manage global configurations.

• basePath is used to manage common root path. Great usage is for your static API endpoint.

    FuelManager.instance.basePath = "https://httpbin.org"
  
    // Later
    Fuel.get("/get").response { request, response, result ->
        //make request to https://httpbin.org/get because Fuel.{get|post|put|delete} use FuelManager.instance to make HTTP request
    }

• baseHeaders is to manage common HTTP header pairs in format of Map<String, String>.

  • The base headers are only applied if the request does not have those headers set.

    FuelManager.instance.baseHeaders = mapOf("Device" to "Android")

• Headers can be added to a request via various methods including

  • fun header(name: String, value: Any): Request: request.header("foo", "a")

  • fun header(pairs: Map<String, Any>): Request: request.header(mapOf("foo" to "a"))

  • fun header(vararg pairs: Pair<String, Any>): Request: request.header("foo" to "a")

  • operator fun set(header: String, value: Collection<Any>): Request: request["foo"] = listOf("a", "b")

  • operator fun set(header: String, value: Any): Request: request["foo"] = "a"

• By default, all subsequent calls overwrite earlier calls, but you may use the appendHeader variant to append values to existing values.

  • In earlier versions a mapOf overwrote, and varargs pair did not, but this was confusing.

• Some of the HTTP headers are defined under Headers.Companion and can be used instead of literal strings.

    Fuel.post("/my-post-path")
        .header(Headers.ACCEPT, "text/html, */*; q=0.1")
        .header(Headers.CONTENT_TYPE, "image/png")
        .header(Headers.COOKIE to "basic=very")
        .appendHeader(Headers.COOKIE to "value_1=foo", Headers.COOKIE to "value_2=bar", Headers.ACCEPT to "application/json")
        .appendHeader("MyFoo" to "bar", "MyFoo" to "baz")
        .response { /*...*/ }
  
     // => request with:
     //    Headers:
     //      Accept: "text/html, */*; q=0.1, application/json"
     //      Content-Type: "image/png"
     //      Cookie: "basic=very; value_1=foo; value_2=bar"
     //      MyFoo: "bar, baz"

• baseParams is used to manage common key=value query param, which will be automatically included in all of your subsequent requests in format of Parameters (Any is converted to String by toString() method)

    FuelManager.instance.baseParams = listOf("api_key" to "1234567890")
  
    // Later
    Fuel.get("/get").response { request, response, result ->
        //make request to https://httpbin.org/get?api_key=1234567890
    }

• client is a raw HTTP client driver. Generally, it is responsible to make Request into Response. Default is HttpClient which is a thin wrapper over java.net.HttpUrlConnection. You could use any httpClient of your choice by conforming to client protocol, and set back to FuelManager.instance to kick off the effect.

• keyStore is configurable by user. By default it is null.

• socketFactory can be supplied by user. If keyStore is not null, socketFactory will be derived from it.

• hostnameVerifier is configurable by user. By default, it uses HttpsURLConnection.getDefaultHostnameVerifier().

• requestInterceptors responseInterceptors is a side-effect to add to Request and/or Response objects.

  • For example, one might wanna print cUrlString style for every request that hits server in DEBUG mode.

      val manager = FuelManager()
      if (BUILD_DEBUG) {
          manager.addRequestInterceptor(cUrlLoggingRequestInterceptor())
      }
      val (request, response, result) = manager.request(Method.GET, "https://httpbin.org/get").response() //it will print curl -i -H "Accept-Encoding:compress;q=0.5, gzip;q=1.0" "https://httpbin.org/get"

  • Another example is that you might wanna add data into your Database, you can achieve that with providing responseInterceptors such as

      inline fun <reified T> DbResponseInterceptor() =
          { next: (Request, Response) -> Response ->
              { req: Request, res: Response ->
                  val db = DB.getInstance()
                  val instance = Parser.getInstance().parse(res.data, T::class)
                  db.transaction {
                      it.copyToDB(instance)
                  }
                  next(req, res)
              }
          }
    
      manager.addResponseInterceptor(DBResponseInterceptor<Dog>)
      manager.request(Method.GET, "https://www.example.com/api/dog/1").response() // Db interceptor will be called to intercept data and save into Database of your choice

Test mode

Testing asynchronized calls can be somehow hard without special care. That's why Fuel has a special test mode with make all the requests blocking, for tests.

Fuel.testMode {
    timeout = 15000 // Optional feature, set all requests' timeout to this value.
}

In order to disable test mode, just call Fuel.regularMode()

RxJava Support

• Fuel supports RxJava right off the box.

    "https://www.example.com/photos/1".httpGet()
      .toRxObject(Photo.Deserializer())
      .subscribe { /* do something */ }

• There are 6 extensions over Request that provide RxJava 2.x Single<Result<T, FuelError>> as return type.

    fun Request.toRxResponse(): Single<Pair<Response, Result<ByteArray, FuelError>>>
    fun Request.toRxResponseString(charset: Charset): Single<Pair<Response, Result<String, FuelError>>>
    fun <T : Any> Request.toRxResponseObject(deserializable: Deserializable<T>): Single<Pair<Response, Result<T, FuelError>>>
  
    fun Request.toRxData(): Single<Result<ByteArray, FuelError>>
    fun Request.toRxString(charset: Charset): Single<Result<String, FuelError>>
    fun <T : Any> Request.toRxObject(deserializable: Deserializable<T>): Single<Result<T, FuelError>>

LiveData Support

• Fuel supports LiveData

  Fuel.get("www.example.com/get")
    .liveDataResponse()
    .observe(this) { /* do something */ }

Routing Support

In order to organize better your network stack FuelRouting interface allows you to easily setup a Router design pattern.

sealed class WeatherApi: FuelRouting {

    override val basePath = "https://www.metaweather.com"

    class weatherFor(val location: String): WeatherApi() {}

    override val method: Method
        get() {
            when(this) {
                is weatherFor -> return Method.GET
            }
        }

    override val path: String
        get() {
            return when(this) {
                is weatherFor -> "/api/location/search/"
            }
        }

    override val params: Parameters?
        get() {
            return when(this) {
                is weatherFor -> listOf("query" to this.location)
            }
        }

    override val headers: Map<String, String>?
        get() {
            return null
        }

}


// Usage
Fuel.request(WeatherApi.weatherFor("london"))
    .responseJson { request, response, result ->
        result.fold(success = { json ->
            Log.d("qdp success", json.array().toString())
        }, failure = { error ->
            Log.e("qdp error", error.toString())
        })
    }

Coroutines Support

Coroutines module provides extension functions to wrap a response inside a coroutine and handle its result. The coroutines-based API provides equivalent methods to the standard API (e.g: responseString() in coroutines is awaitStringResponse()).

runBlocking {
    val (request, response, result) = Fuel.get("https://httpbin.org/ip").awaitStringResponse()

    result.fold(
        { data -> println(data) /* "{"origin":"127.0.0.1"}" */ }, 
        { error -> println("An error of type ${error.exception} happened: ${error.message}") }
    )
}

There are functions to handle Result object directly too.

runBlocking {
    Fuel.get("https://httpbin.org/ip")
        .awaitStringResult()
        .fold(
            { data -> println(data) /* "{"origin":"127.0.0.1"}" */ }, 
            { error -> println("An error of type ${error.exception} happened: ${error.message}") }
        )
}

It also provides useful methods to retrieve the ByteArray,String or Object directly. The difference with these implementations is that they throw exception instead of returning it wrapped a FuelError instance.

runBlocking {
    try {
        println(Fuel.get("https://httpbin.org/ip").awaitString()) // "{"origin":"127.0.0.1"}"
    } catch(exception: Exception) {
        println("A network request exception was thrown: ${exception.message}")
    }
}

Handling objects other than String (awaitStringResponse()) or ByteArray (awaitByteArrayResponse()) can be done using awaitObject, awaitObjectResult or awaitObjectResponse.

data class Ip(val origin: String)

object IpDeserializer : ResponseDeserializable<Ip> {
    override fun deserialize(content: String) =
        jacksonObjectMapper().readValue<Ip>(content)
}

runBlocking {
    Fuel.get("https://httpbin.org/ip")
        .awaitObjectResult(IpDeserializer)
        .fold(
            { data -> println(data.origin) /* 127.0.0.1 */ }, 
            { error -> println("An error of type ${error.exception} happened: ${error.message}") }
        )
}

runBlocking {
    try {
        val data = Fuel.get("https://httpbin.org/ip").awaitObject(IpDeserializer)
        println(data.origin) // 127.0.0.1
    } catch (exception: Exception) {
        when (exception){
            is HttpException -> println("A network request exception was thrown: ${exception.message}")
            is JsonMappingException -> println("A serialization/deserialization exception was thrown: ${exception.message}")
            else -> println("An exception [${exception.javaClass.simpleName}\"] was thrown")
        }
    }
}

Project Reactor

The Reactor module API provides functions starting with the prefix mono to handle instances of Response, Result<T, FuelError> and values directly (String, ByteArray, Any). All functions expose exceptions as FuelError instance.

Data handling example

Fuel.get("https://icanhazdadjoke.com")
    .header(Headers.ACCEPT to "text/plain")
    .monoString()
    .subscribe(::println)

Error handling example

data class Guest(val name: String)

object GuestMapper : ResponseDeserializable<Guest> {
    override fun deserialize(content: String) =
        jacksonObjectMapper().readValue<Guest>(content)
}

Fuel.get("/guestName").monoResultObject(GuestMapper)
    .map(Result<Guest, FuelError>::get)
    .map { (name) -> "Welcome to the party, $name!" }
    .onErrorReturn("I'm sorry, your name is not on the list.")
    .subscribe(::println)

Response handling example

FuelManager.instance.basePath = "https://httpbin.org"

Fuel.get("/status/404").monoResponse()
    .filter(Response::isSuccessful)
    .switchIfEmpty(Fuel.get("/status/200").monoResponse())
    .map(Response::statusCode)
    .subscribe(::println)

Other libraries

If you like Fuel, you might also like other libraries of mine;

• Result - The modelling for success/failure of operations in Kotlin

• Fuse - A simple generic LRU memory/disk cache for Android written in Kotlin

• Forge - Functional style JSON parsing written in Kotlin

• ReactiveAndroid - Reactive events and properties with RxJava for Android SDK

Credits

Fuel is brought to you by contributors.

Licenses

Fuel is released under the MIT license.