HTTP

The Hypertext Transfer Protocol (HTTP) is a foundational protocol of the World Wide Web, enabling communication between clients (such as web browsers) and servers. It is an application-layer protocol designed for transmitting hypermedia documents, such as HTML, images, and videos. HTTP follows a request-response model, where clients send requests, and servers return responses.

HTTP is stateless, meaning that each request from a client to a server is processed independently, with no memory of previous interactions unless explicitly managed using mechanisms like cookies or session storage.

HTTP versions

Here are the different HTTP versions with their release dates:

  • HTTP/0.9 (1991): The first version, focused on transferring raw HTML content. Supported only GET requests and lacked headers or metadata.
  • HTTP/1.0 (1996): Introduced metadata (headers), support for POST and HEAD methods, and status codes. Each request required a separate TCP connection.
  • HTTP/1.1 (1997): Introduced persistent connections (keep-alive), chunked transfer encoding, and pipelining. Became the most widely used version for decades.
  • HTTP/2 (2015): Focused on performance improvements, such as multiplexing (sending multiple requests over a single connection), header compression, and prioritization.
  • HTTP/3 (2020): Builds upon HTTP/2 but replaces TCP with QUIC, a protocol based on UDP, to reduce latency and improve connection resilience.

How HTTP Works

HTTP operates on a client-server model:

  • Client: Initiates the communication by sending an HTTP request. Examples: Web browsers (e.g., Chrome, Firefox), mobile apps, or API clients.
  • Server: Processes the request and sends back an HTTP response containing the requested resource or an error message.

Key Components of an HTTP Request

An HTTP request consists of:

  • Request Line: Specifies the HTTP method, target resource (URL), and protocol version (e.g., GET /index.html HTTP/1.1).
  • Headers: Metadata about the request (e.g., User-Agent, Host, Accept).
  • Body: (Optional) Contains data sent with the request, such as form submissions or JSON payloads.

Key Components of an HTTP Response

An HTTP response consists of:

  • Status Line: Indicates the protocol version, status code, and status message (e.g., HTTP/1.1 200 OK).
  • Headers: Metadata about the response (e.g., Content-Type, Content-Length, Server).
  • Body: The content being returned (e.g., HTML, JSON, or images).

HTTP Methods

HTTP defines several methods for different types of actions:

  • GET: Retrieves data from a server.
  • POST: Submits data to a server for processing (e.g., form data).
  • PUT: Updates or replaces a resource on the server.
  • DELETE: Deletes a resource on the server.
  • HEAD: Similar to GET but retrieves only headers, not the body.
  • OPTIONS: Describes the communication options for the target resource.
  • PATCH: Partially updates a resource on the server.
  • TRACE: Echoes the received request for diagnostic purposes.
  • CONNECT: Establishes a tunnel for communication, often used with HTTPS.

HTTP Status Codes

HTTP uses standardized status codes to indicate the outcome of a request:

  • 1xx: Informational

    • 100 Continue: Request received, continue to send.
    • 101 Switching Protocols: Server is switching to a new protocol.

  • 2xx: Success

    • 200 OK: Request succeeded.
    • 201 Created: Resource successfully created.
    • 204 No Content: Request succeeded, no content returned.

  • 3xx: Redirection

    • 301 Moved Permanently: Resource has a new permanent URL.
    • 302 Found: Temporary redirection.
    • 304 Not Modified: Resource not modified since last requested.

  • 4xx: Client Errors

    • 400 Bad Request: Invalid request syntax.
    • 401 Unauthorized: Authentication required.
    • 403 Forbidden: Access to the resource is denied.
    • 404 Not Found: Resource not found.

  • 5xx: Server Errors

    • 500 Internal Server Error: Server encountered an error.
    • 502 Bad Gateway: Invalid response from an upstream server.
    • 503 Service Unavailable: Server is temporarily unavailable.

Features of HTTP

Here are the main features and "charcteristics" of HTTP:

  • Statelessness: HTTP does not retain session information, simplifying protocol design. However, this requires mechanisms like cookies or tokens for session management.
  • Flexible Content Handling: HTTP supports various content types (e.g., HTML, JSON, XML, images, videos) via the Content-Type header.
  • Extensibility: Custom headers and methods can be added to support new functionalities.
  • Security (HTTPS): HTTPS is the secure version of HTTP that uses SSL/TLS to encrypt communication, ensuring confidentiality, integrity, and authentication.

HTTP in everyday use

As aleady said, the HTTP protocol is widely used on the web. Here are some examples of usage:

  • Web Browsing: Browsers use HTTP to fetch and render web pages.
  • APIs: RESTful APIs rely on HTTP for communication between clients and servers. This will be particularly explored in the cloud trainings.
  • File Downloads: Many file transfer services use HTTP as the underlying protocol.
  • IoT Devices: Internet-connected devices often use HTTP to send and receive data. This will be particularly explored in the trainings.
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