HTTP protocol

what is HTTP?¶

• HTTP stands for HyperText Transfer Protocol.
• The HTTP protocol can be used to transfer the data in the form of plain text, hypertext, audio, video, etc on the internet.

features of HTTP¶

• HTTP is connectionless
  • The HTTP client, i.e., a browser initiates an HTTP request and after a request is made, the client waits for the response.
  • Server processes the request and returns the response.
  • Once response is recieved then HTTP client disconnects the connection.
• HTTP is media independent
  • The client has to specify the media type in the request
  • Then server will understand the media request and processes it.
• HTTP is stateless
  • The server and client are aware of each other only during a current request. Afterwards, both of them forget about each other.

HTTP Request¶

• It has two parts HTTP request headers and HTTP request body

HTTP request headers¶

• The request looks something like below

http://127.0.0.1:8000/login/
POST /login/ HTTP/1.1

Host: 127.0.0.1
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/20100101 Firefox/18.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Referer: http://127.0.0.1:8000/login/
Cookie: passx=87e8af376bc9d9bfec2c7c0193e6af70; PHPSESSID=l9hk7mfh0ppqecg8gialak6gt5
Connection: keep-alive
Content-Type: multipart/form-data

HTTP request body¶

• HTTP Message Body is the data bytes transmitted in an HTTP transaction message immediately following the headers if there are any.

HTTP response:¶

• It also has two parts HTTP response headers and HTTP response body

HTTP response headers¶

200 OK
Access-Control-Allow-Origin: *
Connection: Keep-Alive
Content-Encoding: gzip
Content-Type: text/html; charset=utf-8
Date: Mon, 18 Jul 2016 16:06:00 GMT
Etag: "c561c68d0ba92bbeb8b0f612a9199f722e3a621a"
Keep-Alive: timeout=5, max=997
Last-Modified: Mon, 18 Jul 2016 02:36:04 GMT

HTTP response body¶

• The last part of a response is the body. Not all responses have one: responses with a status code that sufficiently answers the request without the need for corresponding payload (like 201 Created or 204 No Content) usually don't.

HTTP status codes¶

• Informational responses (100 – 199)
• Successful responses (200 – 299)
• Redirection messages (300 – 399)
• Client error responses (400 – 499)
• Server error responses (500 – 599)

References:¶

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers
• https://developer.mozilla.org/en-US/docs/Web/HTTP/Status