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2017-07-14 Http

Introduction To Http

HTTP#

Hyper-text transfer protocol

  • Rules about how to communicate - conventions
  • Standards for device communication
  • plaintext protocol

Request#

Request line#
    [verb] [uri] HTTP/[version]

    GET /xml HTTP/1.1
Headers#
    [Header Name]: [Header Value]

    Host: httpbin.org
    User-Agent: telnet
    Accept-Language: en-US
Blank Line#
Request Body#
    data (optional)

Response#

Status Line#
    HTTP/[version] [status code] [status message]

    HTTP/1.1 200 OK
Headers#
    [Header Name]: [Header Value]

    Server: nginx
    Date: ...
    Content-Type: application/xml
Blank line#
Response body / Payload#
    html, json etc..

Stateless#

  • No record of previous interaction
  • Can’t remember previous requests

Cookies and sessions is part of application that uses HTTP, not part of http itself

Querystring#

Only works in a GET request Can add data in uri with ?firstname=Stephen&language=English

Helps server give accurate response, should not change any resource

A POST is used to make a change on the server

Content-Length#

If there is data in a response body the Content-Length will give response in bytes

User Agent#

Identifier for client making the request

Content-Type#

Communicates the way form data has been encoded

application/x-www-form-urlencode communicates that has used url encoded characters

HTML - HyperText Markup Lanugage#

URI vs URL#

URI: /xml URL: http://httpbin.org/xml

URL contains the protocol and the hostname Adds how and where a resource can be found

A URL can be relative <a href="/html"> is relative to current site

HTML Form#

  • method: GET, POST (default is GET)
  • action: relative or absolute url
  • inputs: Named input parameters. Must use the name attribute.

Post form submission: Content-Type and Content-Length is requered

URL Encoded#

Form data is encoded as a query string, that make a querystring ok to send over http