HTTP

Hypertext Transfer Protocol (HTTP) is used for fetching HTML documents and other web-based resources. It follows a model where a client (most commonly a browser) requests content stored on a server.

HTTPS

Instead of HTTP, a more secure version, HTTPS, should be used in order to encrypt information sent between the client and server. This encryption is done with Transport Layer Security (or TLS, formerly SSL). Some benefits of HTTPS include:

  • Financial data, like credit card information or bank account numbers, are protected from interception.
  • Domain-ownership can be better verified by users.
  • A growing standard of trust around sites that use HTTPS.

Websites can be certified with HTTPS so that browsers “know” the official site for a person, business, etc. These certifications are approved and signed by a trusted certificate authority (CA).

Requests

HTTP requests are stateless, meaning that all requests are independent and have no knowledge of one another. Requests contain the following parts:

  • The HTTP method being used (more information shortly).
  • The requested URL along with any queries or parameters.
  • The HTTP version, such as 1.1 or 2.0.
  • Any header information such as:
    • The referer that tells the URL where the request came from.
    • Any user agent information about the requesting client.
    • A unique host name that is ideal for many pages on one server.
    • Cookie data about the request.
  • A response-like body that contains the resource to be sent (common with the POST method).

An HTTP client requests information specific URLs using four primary methods:

Method Description
GET Requests data, content, or other resources from the server.
POST Sends data, content, or other resources to the server.
PUT Sends updates for existing content on the server.
DELETE Deletes specific content from the server.

Responses

If the server is able to connect with the client and fulfill its request, it will send back a response that includes the following parts:

  • The version of HTTP being used.
  • Headers similar to the ones used for HTTP requests.
  • A body that contains the successfully requested resource.
  • A status code with a message explaining why the request succeeded or failed.

A breakdown of response status codes is shown below.

Informational

Status Code Name Description
100 Continue The request should continue or be ignored if finished.
102 Processing The server is currently processing the request; no response yet.

Successful

Status Code Name Description
200 OK The request is successful and a response was sent.
202 Accepted Processing not yet finished but request was accepted.

Redirection

Status Code Name Description
301 Moved Permanently The resource URL was changed and the new one was sent in the response.
304 Not Modified Used by caches for serving the same, unmodified content.

Client Errors

Status Code Name Description
400 Bad Request Invalid request based on client-side error (invalid syntax, URL, etc.).
401 Unauthorized Invalid client credentials, such as an API key.
404 Not Found Server couldn’t find resource (e.g. invalid URL).
408 Request Timeout The request is taking too long to finish.

Server Errors

Status Code Name Description
500 Internal Server Error Error occurred on the server-side.
502 Bad Gateway Invalid response from a gateway or proxy server.

Caches and Proxies

HTTP can be used for improving web performance with caches and proxy servers.

Client browsers can use caches for serving content instead of making repeated requests for the same content. Examples of caches include:

  • CDNs that retain copies of web content and serve from close network connections.
  • Proxy browser caches, like ones used in progressive web apps that allow a single user to cache and access content offline.
  • Shared proxy caches that store resources for multiple users (internet service provider, company staff network, etc.).

Proxies are used to mask a client’s IP address by assigning one to a proxy server and have requests sent from there.

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