The easiest HTTP networking library for Kotlin/Android

Fuel

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
RxJava 2.x support out of the box
Google Components LiveData support
Built-in object serialization module (Gson, Jackson, Moshi, Forge) sparkles
Support Kotlin's Coroutines module
API Routing

Installation

Dependency - fuel

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

Dependency - fuel-android

Android SDK - Android SDK

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-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

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
}

Sample

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

Quick Glance Usage

Async mode

Kotlin

//an extension over string (support GET, PUT, POST, DELETE with httpGet(), httpPut(), httpPost(), httpDelete())
"http://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 = "http://httpbin.org"
"/get".httpGet().responseString { request, response, result ->
    //make a GET to http://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("http://httpbin.org/get").responseString { request, response, result ->
	//do something with response
	result.fold({ d ->
	    //do something with data
	}, { err ->
	    //do something with error
	})
}

Java

//get
Fuel.get("http://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) = "http://httpbin.org/get".httpGet().responseString() // result is Result<String, FuelError>

Java

try {
    Triple<Request, Response, String> data = Fuel.get("http://www.google.com").responseString();
    Request request = data.getFirst();
    Response response = data.getSecond();
    Result<String,FuelError> text = data.getThird();
} catch (Exception networkError) {

}

Detail Usage

GET

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

//if you have body to post it manually
Fuel.post("http://httpbin.org/post").jsonBody("{ \"foo\" : \"bar\" }").response { request, response, result ->
}

PUT

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

DELETE

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

HEAD

Fuel.head("http://httpbin.org/get").response { request, response, result ->
   // request body should be empty.
}

PATCH

The default client is HttpClient which is a thin wrapper over java.net.HttpUrlConnnection. java.net.HttpUrlConnnection does not support a PATCH 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("http://httpbin.org/patch").response { request, response, result ->
   // request body should be empty.
}

Debug Logging

Use toString() method to Log (request|response)

Log.d("log", request.toString())

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

//response
<-- 200 (http://httpbin.org/get?key=value)

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

Log.d("cUrl log", request.cUrlString())

//print
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" "http://httpbin.org/post"

Parameter Support

URL encoded style for GET & DELETE request

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

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

Array support for GET requests

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

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

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

Fuel.put("http://httpbin.org/put", listOf("foo" to "foo", "bar" to "bar")).response { request, response, result ->
    //http body includes 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

val timeout = 5000 // 5000 milliseconds = 5 seconds.
val timeoutRead = 60000 // 60000 milliseconds = 1 minute.

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

Java

int timeout = 5000 // 5000 milliseconds = 5 seconds.
int timeoutRead = 60000 // 60000 milliseconds = 1 minute.
Fuel.get("http://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("http://httpbin.org/bytes/32768").destination { response, url ->
    File.createTempFile("temp", ".tmp")
}.response { req, res, result ->

}

Fuel.download("http://httpbin.org/bytes/32768").destination { response, url ->
    File.createTempFile("temp", ".tmp")
}.progress { readBytes, totalBytes ->
    val progress = readBytes.toFloat() / totalBytes.toFloat()
}.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 ->
    // calls to http://example.com/api/put with PUT

}

//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 "mail@example.com", "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("http://httpbin.org/basic-auth/$user/$password").authenticate(username, password).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("http://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("http://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


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

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

}

//Use httpGet extension
"http://www.example.com/user/1".httpGet().responseObject(User.Deserializer()) { req, res, result ->
    //result is of type Result<User, Exception>
    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 module in your dependency block.


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

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

public fun deserialize(bytes: ByteArray): T?

public fun deserialize(inputStream: InputStream): T?

public fun deserialize(reader: Reader): T?

public 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"

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>>.

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

Headers can be add to a request via the methods fun header(pairs: Map<String, Any>?): Request
or fun header(vararg pairs: Pair<String, Any>?).
The latter method does support multiple values for the same key however as
fun header(pairs: Map<String, Any>?): Request takes a map this method can not support multiple
values for the same key as per the definition of the map.

Fuel.get("/get").response { request, response, result ->
    //make request to https://httpbin.org/get with global device header (Device : Android)
}

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

FuelManager.instance.baseParams = listOf("api_key" to "1234567890")

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.HttpUrlConnnection. 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, "http://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.

"http://www.example.com/photos/1".httpGet().rx_object(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.rx_response(): Single<Pair<Response, Result<ByteArray, FuelError>>>
fun Request.rx_responseString(charset: Charset): Single<Pair<Response, Result<String, FuelError>>>
fun <T : Any> Request.rx_responseObject(deserializable: Deserializable<T>): Single<Pair<Response, Result<T, FuelError>>>

fun Request.rx_data(): Single<Result<ByteArray, FuelError>>
fun Request.rx_string(charset: Charset): Single<Result<String, FuelError>>
fun <T : Any> Request.rx_object(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: List<Pair<String, Any?>>?
        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")
        }
    }
}