HTTP Request and HTTP Response and response code

Hello Friends,

Before starting the API Testing a tester must know what is HTTP Request and HTTP response, so this article mainly cover :
HTTP Request
HTTP Response

The HTTP Protocol :

HTTP : Hypertext Transfer Protocol

The HTTP is an application layer protocol(OSI Model) that allows web-based applications to communicate and exchange data.

OSI Layers are as below:
Application
Presentation Session
Transport
Network
Data Link
Physical

OSI model in detailed view :

What is HTTP?

The HTTP is the messenger of the web
It is a TCP/IP based protocol
It is used to deliver content for example images, videos, audios, documents etc.
The computer that communicate via the HTTP must speak the http protocol

Three Important things about HTTP

1). HTTP is connectionless means after making the request, the client disconnect from the server, then when the response is ready the server re-establish the connection again and deliver the response.
2). The HTTP can deliver any sort of data, as long as the two computers are able to read it.
3). The HTTP is a stateless means the client and server know about each other just during the current request, it is closes and the two computers want to connect again, they need to provide information to each other anew, and the connection is handled as the very first one.

Key points :

1).The HTTP is a TCP/IP based application layer protocol that allows web based applications to communicate and exchange data.
2).The computers that communicate via the HTTP must speak the http protocol.
3). The http is stateless, connectionless and can deliver any data.
4).We use the http protocol bacause it is a convenient way to quickly and reliably move data on the web.
5). The request response cycle works on the web via http messages.
6). A http message contains three sections the start line, the header and the body.
7).The http request message differs from the http response messages.


Cycle of HTTP Request & Response

HTTP Request :

An HTTP client sends an HTTP request to a server and basically this request is a packet of information.
This packet ave binary data sent by the client to the server.

HTTP Request contains following three things :

1). Request Line
2). zero or more header (General|Request|Entity) fields followed by CRLF
and an empty line(i.e. a line with nothing preceding the CRLF)
indicating the end of header fieds
3). Message body of request (Optionally)

Two HTTP Request Methods:

GET and POST

Two commonly used methods for a request-response between a client and server are: GET and POST.
GET - Requests data from a specified resource
POST - Submits data to be processed to a specified resource

Request line have Request Method, Request URI, HTTP Protocol

Request Header : In the request section, whatever follows Request Line till before Request Body everything is a Header.
Headers are used to pass additional information about the request to the server.

Request Body is the part of the HTTP Request where additional content can be sent to the server.
For example, a file type of JSON or XML.

Let's better understand by below Image :

HTTP Response :

After successfully receiving and interpreting a request message, server responds with a HTTP response message.
This response is the packet of information sent by server to the client.
As like HTTP Request, HTTP Response also have three things :

1).A status Line
2).Zero or more header (Genreal|Response|Entity) fields followed by CRLF
An empty line (i.e. a line with nothing preceding the CRLF)
indicating the end of the header fields
3). Message Body (optionally)

Status line has , HTTP Protocol version, Status code like 200, and Status message as OK,
Response header, Response Header also contains zero or more Header lines. However, it is very uncommon to have zero Headers in the response. Lines just after the Status Line and before the Response Body are all Response Headers lines.
Response Body , Response Body contains the resource data that was requested by the client.
Note: Response Body contains text in JSON format, as one of the Response headers suggested.
can better understood by below image :

HTTP Staus code :

1xx Informational response :
100 Continue
101 Switching Protocol
102 Processing
103 Early Hints

2xx Success :
200 OK
201 Created
202 Accepted
203 Non-Autoritative Information
204 No Content
205 Reset Content
206 Partial Content
207 Multi-Status
208 Already Reorted
226 IM Used

3xx Redirection :
300 Multiple choices
301 Moved Permanently
302 Found
303 see other
304 Not Modified
305 Use Proxy
306 Switch Proxy
307 Temporary Redirect
308 Permanent Redirect

4xx Client errors :
400 Bad Request
401 Unauthorized
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout
409 Conflict
410 Gone
411 Length Required
412 Precondition Failed
413 Payload Too Large
414 URI Too Long
415 Unsupported Media Type
416 Range Not Satisfiable
417 Expectation Failed
418 I'm a teapot
421 Misdirected Request
422 Unprocessable Entity
423 Locked
424 Failed Dependency
426 Upgrade Required
428 Precondition Required
429 Too Many Requests
431 Request Header Fields Too Large
451 Unavailable For Legal Reasons

5xx Server errors :
500 Internal Server Error
501 Not Implemented
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
505 HTTP Version Not Supported
506 Variant Also Negotiates
507 Insufficient Storage
508 Loop Detected
510 Not Extended
511 Network Authentication Required

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