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HyperText Transfer Protocol

Concepts

  • HTTP is a technique of transmitting data in a particular format between a server (destination) and a client (source).
  • Considered stateless i.e. once a request and response has completed, the server doesn't retain any data about the request.
  • Capable of transmitting hypermedia documents as well as hypertext documents.
  • Composed of two parts:
    • Request
      • created by a client
      • contains the request method, the target URL, the HTTP version, optional information (headers), and a body (for some methods)
    • Response
      • created by a server
      • contains the HTTP version, a status code and message the reflects the request outcome, optional information (headers), and a body (for some methods)
  • In a URL, using a fragment identifier #text is like a bookmark on the page or resource allowing the browser to scroll or navigate to that specific location on a page; It's never sent to the server with the request.
  • Semantic URLs use human-readable words.

HTTP Methods

GET

  • Used to retrieve data at a specified resource.
  • Considered a safe and idempotent method.

POST

  • Used to send data to a server to create or update a resource.
  • Non-idempotent.

PUT

  • Used to send data to the API to update or create a resource.
  • Idempotent i.e. unlike POST, calling the same PUT request multiple times will always produce the same result.

PATCH

  • Similar to POST & PUT
  • Only partial modifications are applied to the resource.
  • Non-idempotent.

DELETE

  • Used to delete the resource at the specified URL.

HEAD

  • Almost identical to GET, but without the response body.
  • Useful to check what a GET request will return before actually making a GET request.

OPTIONS

  • Returns data describing what other methods and operations the server supports at the given URL.
  • Good candidate to test for fatal API errors.

TRACE

  • Used to echo the received request back to the client, allowing the client to see what changes or additions have been made by intermediate servers.
  • Used primarily for diagnostic purposes and is not commonly used in regular web development.

Status Codes

  • Help identify the cause of the problem when a web page doesn't load properly.

  • A status consists of a numeric status code and an HTTP reason phrase.

    • e.g. 500: Internal Server Error

  • 100 – 199

    • Informational responses

  • 200 – 299

    • Successful responses

  • 300 – 399

    • Redirection messages

  • 400 – 499

    • Client error responses

  • 500 – 599

    • Server error responses

Ports

  • HTTP - 80
  • HTTPS - 443

Further

Learn 🧠

Videos 🎥

HTTP Status Codes Explained In 5 Minutes (YouTube)