A Retrofit inspired WebSocket client for Kotlin, Java, and Android

Scarlet

A Retrofit inspired WebSocket client for Kotlin, Java, and Android.

Update

We are working on a new version of Scarlet that supports other persistent connection protocols: ServerSentEvent, Socket IO, STOMP, and MQTT. It can be found on the 0.2.x branch.

Tutorial

• Taming WebSocket with Scarlet
• A talk at Conference for Kotliners

Usage

In this example, we read the realtime Bitcoin price from Gdax WebSocket Feed. For more information, please check out the demo app.

Declare a WebSocket client using an interface:

interface GdaxService {
	@Receive
	fun observeWebSocketEvent(): Flowable<WebSocket.Event>
	@Send
	fun sendSubscribe(subscribe: Subscribe)
	@Receive
 	fun observeTicker(): Flowable<Ticker>
}

Use Scarlet to create an implementation:

val scarletInstance = Scarlet.Builder()
    .webSocketFactory(okHttpClient.newWebSocketFactory("wss://ws-feed.gdax.com"))
    .addMessageAdapterFactory(MoshiMessageAdapter.Factory())
    .addStreamAdapterFactory(RxJava2StreamAdapterFactory())
    .build()

val gdaxService = scarletInstance.create<GdaxService>()

Send a Subscribe message upon connection open and the server will start streaming tickers which contain the latest price.

val BITCOIN_TICKER_SUBSCRIBE_MESSAGE = Subscribe(
    productIds = listOf("BTC-USD"),
    channels = listOf("ticker")
)

gdaxService.observeWebSocketEvent()
    .filter { it is WebSocket.Event.OnConnectionOpened<*> }
    .subscribe({
        gdaxService.sendSubscribe(BITCOIN_TICKER_SUBSCRIBE_MESSAGE)
    })

gdaxService.observeTicker()
    .subscribe({ ticker ->
        Log.d("Bitcoin price is ${ticker.price} at ${ticker.time}")
    })

Android

Scarlet is driven by a StateMachine.

TODO

Download

Scarlet is available via Maven Central.

Snapshots of the development version are available in Sonatype’s snapshots repository.

Maven:

<dependency>
    <groupId>com.tinder.scarlet</groupId>
    <artifactId>scarlet</artifactId>
    <version>0.1.9</version>
</dependency>

Gradle:

implementation 'com.tinder.scarlet:scarlet:0.1.9'

Plug-in Roadmap

WebSocket.Factory

• OkHttpClient
• MockHttpServer

MessageAdapter.Factory

• moshi
• gson
• protobuf
• jackson
• simple-xml

StreamAdapter.Factory

• RxJava2
• RxJava1
• Kotlin Coroutine

Lifecycle

• AndroidLifecycle

BackoffStrategy

• Linear
• Exponential
• ExponentialWithJitter

Copyright

Copyright (c) 2018, Match Group, LLC
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
    * Neither the name of Match Group, LLC nor the names of its contributors
      may be used to endorse or promote products derived from this software
      without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL MATCH GROUP, LLC BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.