Appium architecture (How Appium works internally)

Appium Architecture 

Appium is a cross-platform automation tool, API of it supports both OS (Android and iOS) test scripts.It is tested on simulators (iOS,), emulators (Android), and real devices (iOS, Android)  

Appium is an HTTP server written in Node.js that creates and handles WebDriver sessions.The Appium web server follows the same approach as the Selenium WebDriver, which receives HTTP requests from client libraries through JSON and then handles those requests in different ways

 JSON wire protocol

The JSON wire protocol (JSONWP) is a transport mechanism created by WebDriver developers. This wire protocol is a specific set of predefined, standardized endpoints exposed via a RESTful API.  

Appium implements the Mobile JSONWP, the extension to the Selenium JSONWP, and it controls the different mobile device behaviors, such as installing/uninstalling apps over the session

Let’s have a look at some of the endpoints from the API which are used to interact with mobile applications:

• l /session/:sessionId
• l /session/:sessionId/element
• l /session/:sessionId/element 
• l /session/:sessionId/element/:id/click

 Appium provides client libraries similar to WebDriver that act as an interface to the REST API. These libraries have functions similar to the following method:

AppiumDriver.getPageSource();

Appium on Android

On an Android device, Appium uses the UIAutomator framework to automate the apps. UIAutomator is a framework that is developed by the Android developers to test the Android user interface.

1. Appium client (C# or Java or python .etc) connects with Appium Server and communicate via JSON Wire Protocol

2. Appium Server then creates a automation session for the client and also checks the desired capabilities of client and connects with respective vendor-provided frameworks like UIAutomator.

3. UIAutomator will then communicate with bootstrap.jar which is running in Emulator/Real device for performing client operations

4. Here, bootstrap.jar plays the role of a TCP server, which we can use to send the test command in order to perform the action on the Android device using UIAutomator.

After the execution of the command, the client sends back the message to the Appium server with the log details of the executed command.

Appium on iOS

On an iOS device, Appium uses Apple’s UIAutomation API to interact with the UI elements. UIAutomation is a JavaScript library provided by Apple to write test scripts; Appium utilizes these same libraries to automate iOS apps.

1.Appium client (Java or Python) connects with Appium Server and communicate via JSON Wire Protocol.

2.Appium Server then creates a automation session for the client and also checks the desired capabilities of client and connects with respective vendor-provided framework like UIAutomation

3.UIAutomation will then communicate with bootstrap.js which is running in Simulator/Real device for performing client operations

4.Bootstrap.js will perform action on our AUT (Application Under Test)

After the execution of the command, the client sends back the message to the Appium server with the log details of the executed command.