HTTP Tutorial

Introduction to HTTP

HTTP (HyperText Transfer Protocol) is an application-layer protocol used for distributed, collaborative, hypermedia information systems. It is the foundation of data communication for the World Wide Web (WWW) and is designed to ensure communication between clients and servers. HTTP is one of the most commonly used protocols on the internet.

HTTP Tutorial0

How HTTP Works

HTTP operates over the TCP/IP protocol to transmit data (HTML files, images, query results, etc.). Its initial design aimed to provide a method for publishing and receiving HTML pages, with resources requested via HTTP or HTTPS identified by Uniform Resource Identifiers (URIs).

HTTP Request-Response Cycle

HTTP functions on a request-response model where the client (usually a web browser) sends a request to the server, which then returns the requested resource. These resources can be web pages, images, audio files, videos, etc.

HTTP uses a client-server model:

Client: Sends the request
Server: Returns the response


The typical steps of an HTTP request-response cycle are:

  • Establishing a Connection: The client and server establish a connection, traditionally over TCP/IP. HTTP/2 and HTTP/3 use more advanced transport protocols, such as the binary protocol based on TCP (HTTP/2) or the QUIC protocol based on UDP (HTTP/3).
  • Sending a Request: The client sends a request, including the URL, request method (GET, POST, PUT, DELETE, etc.), request headers (e.g., Accept, User-Agent), and an optional request body (for POST or PUT requests).
  • Processing the Request: The server processes the request, retrieves the relevant resource, performs necessary operations, which might involve database retrieval, generating dynamic content, or returning static files.
  • Sending a Response: The server sends back the response, which includes a status code (indicating success or failure), response headers (e.g., Content-Type, Content-Length), and an optional response body (e.g., an HTML page, image data).
  • Closing the Connection: After completing the request-response cycle, the connection can be closed unless a persistent connection (like keep-alive in HTTP/1.1) is used.


HTTP Methods

HTTP methods specify the actions the client can perform on the server's resources. The main HTTP methods are:

  • GET: Retrieve a specified resource from the server.
  • POST: Submit data to the server, typically used for form submissions.
  • PUT: Replace all current representations of the target resource with the request payload.
  • DELETE: Remove the specified resource.
  • HEAD: Similar to GET, but only fetches the headers, not the resource content.


HTTP Status Codes

HTTP status codes are the server's responses to the client's requests, categorized as:

  • 1xx (Informational): Request received, continuing process.
  • 2xx (Success): Request successfully received, understood, and accepted.
  • 3xx (Redirection): Further action needs to be taken to complete the request.
  • 4xx (Client Error): Request contains bad syntax or cannot be fulfilled.
  • 5xx (Server Error): Server failed to fulfill a valid request.


HTTP Versions

Several versions of HTTP are widely used:

  • HTTP/1.1: Supports persistent connections, allowing multiple requests/responses over a single TCP connection.
  • HTTP/2: Uses binary framing and multiplexing, enabling multiple streams within a single connection.
  • HTTP/3: Based on the QUIC protocol, designed to reduce latency and improve speed and security.


Security

HTTP itself is not secure as the transmitted data is not encrypted, making it susceptible to eavesdropping or tampering. HTTPS addresses this by adding SSL/TLS protocols for encryption and authentication.