Top HTTP Interview Questions and Answers

What is HTTP?

HTTP (Hypertext Transfer Protocol) is the foundation of data communication on the World Wide Web. It's a set of rules governing how web browsers (clients) and web servers exchange information. HTTP is used to transfer various types of data, including HTML, CSS, JavaScript, images, videos, and more. While highly versatile, basic HTTP lacks built-in security features.

HTTP Request Messages

An HTTP request message is sent from a client (like a web browser) to a server to initiate an action. It consists of:

  • Request Line: Contains the HTTP method (GET, POST, etc.), the requested resource (URI), and the HTTP version.
  • Request Headers: Provide additional information about the request (e.g., user agent, accepted content types).
  • Request Body (optional): Contains data being sent to the server (e.g., form data).

HTTP Request Methods

HTTP defines various methods to specify the type of action to be performed:

  • GET: Retrieves data.
  • HEAD: Retrieves headers only (like GET but without the body).
  • POST: Sends data to the server (often form data).
  • PUT: Replaces all current representations of a resource.
  • DELETE: Deletes a resource.
  • CONNECT: Establishes a tunnel to a server.

HTTP Status Codes

HTTP status codes are three-digit numbers that indicate the result of a client's request. The first digit categorizes the response:

  • 1xx: Informational
  • 2xx: Success
  • 3xx: Redirection
  • 4xx: Client error
  • 5xx: Server error

Persistent Connections (Keep-Alive)

Persistent connections (introduced in HTTP/1.1) reuse the same TCP connection for multiple requests and responses, improving efficiency compared to HTTP/1.0 where a new connection was required for each request.

Session State in HTTP

HTTP is stateless; each request is treated independently. Session management techniques (like cookies or session IDs) are used to maintain state across multiple requests from a client.

HTTP Messages

HTTP uses request and response messages for communication between clients and servers. These messages follow a specific format, including headers and a body.

HTTP cURL

cURL is a command-line tool for transferring data using various protocols, including HTTP. It's useful for testing APIs and other network tasks.

HTTP Responses

An HTTP response message is sent from a server to a client, providing the requested resource or information about the request's outcome. It includes:

  • Status Line: Indicates the success or failure of the request (status code and reason phrase).
  • Headers: Provide additional information about the response (content type, length, etc.).
  • Body (optional): Contains the requested data.

HTTP Security

Basic HTTP is not secure; sensitive data should be transmitted using HTTPS (HTTP Secure), which utilizes TLS (Transport Layer Security) for encryption.

HTTP Status Codes: Examples

  • 200 OK: Request was successful.
  • 201 Created: A new resource was created.
  • 300 Multiple Choices: Multiple options for the requested resource.
  • 400 Bad Request: The request was malformed.
  • 401 Unauthorized: Authentication is required.
  • 405 Method Not Allowed: The specified method is not allowed.
  • 408 Request Timeout: The server timed out waiting for the request.
  • 500 Internal Server Error: An error occurred on the server.

100 Continue Status Code

The 100 Continue status code is an informational response indicating that the server has received the initial part of a request and that the client should continue sending the rest of the request.

IP and OSI Layers

IP (Internet Protocol) belongs to the Network Layer (Layer 3) of the OSI (Open Systems Interconnection) model.

Roles of HTTP

HTTP's primary role is to transfer hypertext (HTML) documents. It has evolved to support various content types and is fundamental to web communication.

HTTPS

HTTPS (HTTP Secure) uses TLS (Transport Layer Security) to encrypt communication between clients and servers, protecting data confidentiality and integrity.

Content Negotiation in HTTP

Content negotiation is the process of selecting the best representation of a resource for a given client request. This involves considering factors like the client's accepted content types and language preferences.

Types of Content Negotiation

  • Server-driven: The server determines the best representation.
  • Agent-driven: The client (user agent) determines the best representation.
  • Transparent: A combination of server-driven and agent-driven negotiation.

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