What are request headers?

Request Headers are additional information sent by the client (browser or other application) to the server as part of an HTTP request. They contain metadata about the request, client, and the resource being requested.

Main functions of request headers:

• Sending client information: Browser type, operating system, supported languages (User-Agent, Accept-Language).
• Cache control: Indicating conditions for obtaining an updated resource (If-None-Match, If-Modified-Since).
• Authentication: Sending user credentials (Authorization).
• Content negotiation: Indicating preferred response formats (Accept, Accept-Encoding).
• Request body size and type: Information about data sent in the request body (Content-Type, Content-Length).
• Security: Indicating the request source to prevent attacks (Origin, Referer).

Examples of common request headers:

• Host: The domain name of the server to which the request is directed.
• User-Agent: Identifies the client software.
• Accept: Specifies media types the client is willing to accept in response.
• Content-Type: Indicates the media type of the request body.
• Authorization: Contains credentials for authentication (e.g., Bearer token).
• Cookie: Contains HTTP cookies sent by the client to the server.

Example of an HTTP request structure with headers:

GET /index.html HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Connection: keep-alive

In QA context, checking request headers is important for:

• Validating the correctness of sent data.
• Security testing (e.g., checking for necessary headers for authorization).
• Debugging caching issues and content type support.
• Traffic analysis to understand client behavior.