ITPE001 - APIs

Web Request and Response

Publish Date: Sep 29, 2023

What is HTTP?

HTTP or Hypertext Transfer Protocol is an application layer protocol that allows web-based applications to communicate and exchange data between each other.

Understanding the HTTP Request and Response Cycle

When a user search or access a website it starts a chain of events that allow various devices or software to communicate with each other. This is done by done by a user on a client device or software (a web browser for example) by creating a string or a URL.
The URL is then read by the software on the client’s device and then the browser will create a request for the URL that the user typed in the browser (https://mndrewdevlog.web.app/) The client will send an HTTP request to the server with the following information: HTTP Method, Requested Resource, Resource Headers.
The Server receives the HTTP request and processes it.
1. The server will check if the request is valid and will generate a response.
The Server sends an HTTP response to the client together with the following information:
- HTTP Status Code
- Response Headers
- Response Body
The client receives the HTTP response and processes it.
- If the request is successful, it will show the response body or the requested resource.
- However, if the response it is unsuccessful an error message will be displayed.
  - Example - Error 404: Page or Resource Not Found

Definition of Terms

Client
- a computer device or software that tries to access a resource from a server.
Server
- a computer or software that provides resources to other computers called clients.
Path
- A path is a part of the URL (Uniform Resource Locator)
- This specifies the location of a specific resource on the server.
Example
- Given URL: https://mndrewdevlog.web.app/blog/assessment/web-request-and-response/
- Domain Name: mndrewdevlog.web.app
- Path to a resource: /blog/assessment/web-request-and-response/
Verb
- In HTTP a verb pertains to an HTTP Method or HTTP Verb.
- A verb specifies what action is going to be performed on the resource
- List of HTTP Verbs
  - GET
  - PUT
  - POST
  - PUT
  - CONNECT
  - PATCH

What are the common HTTP verbs and what do they do?

Here are 5 common HTTP verbs with their respective operations or Function

Verb	Operations/Function
`GET`	This method requests a specific resource from the web server.
`POST`	This method submits data or information to a specific resource.
`DELETE`	This method deletes a specific resource
`PATCH`	This method updates a resource
`CONNECT`	This method allows a connection tunnel to the server to a specific resource.

Response Status Code Categories

As part of the HTTP Request and Response cycle status codes help indicate whether a request has been completed.

The status codes are categorized into 5 cases with each specific use case.

HTTP Status Code Range	Purpose or Category	Example
`100` - `199`	Informational Responses	`100` - Continue
`200` - `299`	Successful Responses	`200` - OK or Successful
`300` - `399`	Redirect Message	`302` - Redirected
`400` - `499`	Client Error Message	`404` - Not Found
`500` - `599`	Server Error Message	`502` - Bad Gateway

References

Cloudflare, What is HTTP? - https://www.cloudflare.com/learning/ddos/glossary/hypertext-transfer-protocol-http/
Jen Strong, The Request/Response Cycle of the Web - https://medium.com/@jen_strong/the-request-response-cycle-of-the-web-1b7e206e9047
HTTPWG.ORG, HTTP Semantics - https://httpwg.org/specs/rfc9110.html#overview.of.status.codes
MDN Web Docs:
- HTTP Messages - https://developer.mozilla.org/en-US/docs/Web/HTTP/Messages
- HTTP response status codes - https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

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