What is the difference between Protocol and Json Wire Protocol

Question

Protocol: A standard to define a method of exchanging data over a network. If a browser wants to communicate with a server, it has to create an HTTP request and send that HTTP request to the server to convey its request of resources and options. The server receives the request and process it and do the needful and create an HTTP response to send to the browser. The browser has to follow the HTTP specification in creating the HTTP request. The server also has to follow the HTTP specification in creating the HTTP response. This is how the communication between the browser and the server happens in a standard way to avoid conflicts by following the HTTP protocol.

Json Wire Protocol: A client has an object that has to be sent to a server. The client converts this object into a JSON object and sends it to the server. The server parses the JSON object and converts it back to object for use. The server converts the response object into a JSON object and sends it back to the client. The client then converts the JSON object to object for use.

Why the later is called as Json Wire Protocol?

Answer 1

You are pretty correct both about Protocol and JsonWireProtocol. At this point it is worth to mention that, earlier all implementations of WebDriver that communicated with the browser, or a RemoteWebDriver server shall use a common wire protocol. This wire protocol defines a RESTful web service using JSON over HTTP.

JSON Wire Protocol is an abstract specification of how automation behavior like clicking or typing or whatever you actually want to do with your automation script is mapped to selenium or appium or HTTP requests and response. The protocol will assume that the WebDriver API has been "flattened", but there is an expectation that client implementations will take a more Object-Oriented approach, as demonstrated in the existing Java API. The wire protocol is implemented in request/response pairs of "commands" and "responses".

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What is JSON Wire protocol?

JSON (JavaScript Object Notation) is a lightweight format for data exchange between client and server. Applications use JSON objects to send and receive data between each other in the web world. JSON data structure is industry standard and can be used for sending and receiving data as Key & Value pair. Some people say its a very nice alternative for XML. We can save JSON files as .json extension.

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How JSON looks like?

A simple json file looks like below and there are many online editors which can be used to edit and verify JSON structure.

{
 "Student":{
   "FirstName":"Pawan",
   "LastName":"Garia",
   "IdNumber":"12345",
   "City" : "New Delhi",
   "EmailID" : "[email protected]" }
}

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Why JSON Wire Protocol was used in first place?

To implement a client-server architecture which can give us the following benefits.

• You write test in any programming language.
• You can perform or run test on cloud services like SauceLabs, BrowserStack or Selenium Grid setup.
• You are not bound to run test only on the local machine.
• Different Drivers(FirefoxDriver, ChromeDriver) can be crated for browsers and separate implementation by using the same standards.

So client-server implementation requires a standard set of the specification beforehand so that Server and Client should be in sync with each other in term of what is coming and going on request and response. It’s something like a language of communication with each other. So we need some common specification to solve this kind of requirement and the solution was HTTP.

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Why HTTP is the solution?

HTTP is a standard for web and can be a good base for the specification. Every programming language has a good HTTP libraries which can be used for creating client and server for request and response calls.

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How JSON Wire protocol worked with HTTP?

HTTP request and response are generally made of GET and POST requests which is out of scope for this discussion.

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Current status

From Selenium perspective, JSON Wire Protocol is obsolete now and the WebDriver W3C Living Document is the new implementation.

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WebDriver Communication

The WebDriver protocol is organised into commands. Each HTTP request with a method and template defined in the specification represents a single command and hence each command produces a single HTTP response. In response to a command, the remote end will run a series of actions known as remote end steps. These provide the sequences of actions that a remote end takes when it receives a particular command.

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Command Processing

The remote end is an HTTP server reading requests from the client and writing responses typically over a TCP socket. In the specification the communication is modeled as the data transmission between a particular local end and remote end with a connection to which the remote end may write bytes and read bytes. The exact details of how this connection works and how it is established is a bigger topic and out of scope for this question. After a connection has been established, the remote end must read bytes from the connection until a complete HTTP request can be constructed from the data. If it is not possible to construct a complete HTTP request, the remote end must either close the connection, return an HTTP response with status code 500, or return an error with error code unknown error.

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Outro

Difference between JsonWireProtocol mechanisms and the new standards in W3C Living Document when using Selenium