how Selenium uses HTTP commands to automate a browser

To understand how Selenium uses HTTP commands to launch a browser, we'll delve into how the WebDriver protocol works, specifically focusing on how Selenium WebDriver interacts with browser drivers like ChromeDriver through HTTP requests.

WebDriver Protocol

The WebDriver protocol is a set of RESTful HTTP endpoints used by Selenium to communicate with the browser driver. When you write a Selenium script, it sends HTTP requests to the browser driver, which then executes commands in the browser and returns the results.

Here’s a simplified step-by-step explanation of how Selenium launches a browser using HTTP commands:

1. Create a New Session

The process starts by sending a POST request to the browser driver to create a new session. This request contains desired capabilities, which are settings that configure the browser instance.

Example: Launching Chrome

Below is a step-by-step example showing the HTTP requests involved in launching a Chrome browser using Selenium WebDriver.

Step 1: Initialize the WebDriver Session

The client sends a POST request to the ChromeDriver to create a new session.

HTTP Request:

POST /session HTTP/1.1
Host: localhost:9515
Content-Type: application/json

{
  "capabilities": {
    "alwaysMatch": {
      "browserName": "chrome"
    }
  }
}

HTTP Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "value": {
    "sessionId": "1234567890abcdef",
    "capabilities": {
      "browserName": "chrome",
      "browserVersion": "91.0.4472.77",
      ...
    }
  }
}

This response contains the session ID, which will be used for subsequent requests.

Step 2: Navigate to a URL

To navigate to a URL, the client sends a POST request with the session ID to the /url endpoint.

HTTP Request:

POST /session/1234567890abcdef/url HTTP/1.1
Host: localhost:9515
Content-Type: application/json

{
  "url": "http://www.example.com"
}

HTTP Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "value": null
}

Step 3: Perform Actions (e.g., Finding an Element and Clicking It)

To find an element, the client sends a POST request with the session ID to the /element endpoint.

HTTP Request:

POST /session/1234567890abcdef/element HTTP/1.1
Host: localhost:9515
Content-Type: application/json

{
  "using": "css selector",
  "value": "#myButton"
}

HTTP Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "value": {
    "element-6066-11e4-a52e-4f735466cecf": "abcdef1234567890"
  }
}

To click the element, the client sends a POST request with the session ID and the element ID to the /element/{elementId}/click endpoint.

HTTP Request:

POST /session/1234567890abcdef/element/abcdef1234567890/click HTTP/1.1
Host: localhost:9515
Content-Type: application/json

{}

HTTP Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "value": null
}

4. Close the Browser

To close the browser, the client sends a DELETE request with the session ID to the /session/{sessionId} endpoint.

HTTP Request:

DELETE /session/1234567890abcdef HTTP/1.1
Host: localhost:9515

HTTP Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "value": null
}