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HTTP-BASIC

this section is talking about structure of http application

Table of Contents

HTTP

HTTP ( Hyper Text Transfer Protocol ) is a protocol to request and response between client / server

e.g., a browser requests the web page then the server returns it

http

From the application's point of view :

HTTP request contains fields of METHOD, URL, HEADER, BODY

HTTP response contains fields of STATUS, HEADER, BODY

HTTP Examples

Open the Google Chrome then access http://httpbin.org/get. You may see the following attributes from browser network inspector ( F12 )

  • General
    • Remote Address : 54.175.219.8:80
    • Request Url : http://httpbin.org/get
    • Request Method : GET
    • Status Code : 200 OK
  • Request Headers
    • Accept : text/html
    • Accept-Language : zh-TW
    • Host : httpbin.org
    • User-Agent : Chrome/46.0.2490.86
  • Response Headers
    • Content-Length : 620
    • Content-Type : application/json
    • Server : nginx

URL

URL ( Uniform Resource Locator ) is an unique address of a resource on the Internet

URL Examples

  • http://httpbin.org/get
  • https://github.com/
  • http://forum.gamer.com.tw/A.php?bsn=60084
  • http://192.168.0.1/login.htm

URL Parts

For example : http://zh.wikipedia.org:80/w/index.php?title=HelloWorld&printable=yes#paragraph1

field required description example
scheme O transfer protocol http
host O host domain name or ip zh.wikipedia.org
port X host port 80
path X path to the resource /w/index.php
query X additional key-value pairs ?title=HelloWorld&printable=yes
fragment X additional identifier #paragraph1

URL Domain Resolving

How does the zh.wikipedia.org be resolved ?

How does the agent know where its real address is ?

The answer is DNS ( Domain Name Server )

DNS stores key-value pairs of domain name and ip so that agent can ask DNS to get the real ip address of that host. DNS address would be set in OS network configuration by user or DHCP

Method

Client must specify an action when request a resource. This action indicates the purpose of this request.

http-method http-method

Method Examples

  • POST http://example.com/resources : create a new resource with body
  • GET http://example.com/resources/1 : get the resource #1
  • PUT http://example.com/resources/1 : update the resource #1 with body
  • DELETE http://example.com/resources/1 : delete the resource #1

Method List

method idempotent description
GET O read
POST X create
PUT O create or update
PATCH X update
DELETE O delete
HEAD O read header only

idempotent : if an operation returns same result even been executed for multiple times, then this is called idempotent

Method in Browser

User doesn't see the http method when using browser is that the browser use GET when user click link or request any resource by default. The other methods can be triggered by javascript.

Header

Header contains the extra information of the sender by sender's own. It is just a key-value pair so that custom header can be used.

http-header http-header

Header Examples

  • Client Request
    • Accept : text/html
    • Accept-Language : zh-TW
    • Host : httpbin.org
    • User-Agent : Chrome/46.0.2490.86
  • Server Response
    • Content-Length : 620
    • Content-Type : application/json
    • Server : nginx

Some Wellknown Headers

header type description example
Host req domain name of server en.wikipedia.org
User-Agent req user agent string Chrome/46.0.2490.86
Accept req acceptable content types of response text/html
Accept-Charset req acceptable charset of response utf-8
Accept-Language req acceptable human language of response en-US
Cache-Control req, res cache strategy no-cache
Content-Type req, res body MIME type application/json
Content-Length req, res body length in bytes 348
Server res name of server Apache/2.4.1 (Unix)
Expires res response expire date Thu, 01 Dec 1994 16:00:00 GMT
Last-Modified res last modified date of the request target Tue, 15 Nov 1994 12:45:26 GMT

Body

Body is an optional message associated with the request or response

http-body http-body

Body Examples

  • plain

    HelloWorld

  • html

    <html>
  <head>
    <title>Hi there</title>
  </head>
  <body>
    This is a page
  </body>
</html>

  • xml

    <response>
  <id>101502549</id>
  <name>Jason Chiu</name>
</response>

  • json

    {
  "response" : {
    "id" : "101502549",
    "name" : "Jason Chiu"
  }
}

Status

Status is a simple code representing the status of the request after processing

http-status http-status

Status Examples

  • 200 ( OK )
  • 403 ( Forbidden )
  • 404 ( Not Found )
  • 500 ( Internal Server Error )

Some Wellknown Statuses

Statuses can be divided into 5 categories :

  • 1xx : request continuing process
  • 2xx : request success
  • 3xx : request will be redirected
  • 4xx : client error
  • 5xx : server error

2xx

status text description
200 ok request success
201 created request success and a new resource is created
204 no content request success but returns no content

3xx

status text description
302 found requested resource is moved temporarily and server should response that temporary address
304 not modified requested resource is not modified after the specific date if client give that date

4xx

status text description
400 bad request invalid request data
401 unauthorized authentication is required and has failed or has not yet been provided
403 forbidden server is refusing to respond to it
404 not found current required resource could not be found
405 method not allowed request method not supported by that resource

5xx

status text description
500 internal server error generic server error
502 bad gateway server was acting as a gateway or proxy and received an invalid response from the upstream server
503 service unavailable server is currently unavailable

Examples

Open Google Chrome, click F12 then access http://httpbin.org/ip

You can see the following information in ip document in Network inspector

  • Request

    • Method : GET
    • URL : http://httpbin.org/ip
    • Headers
      • Accept : text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
      • Accept-Encoding : gzip, deflate, sdch
      • Accept-Language : zh-TW,zh;q=0.8,en-US;q=0.6,en;q=0.4,ja;q=0.2,zh-CN;q=0.2
      • Connection : keep-alive
      • Host : httpbin.org
      • User-Agent : Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2490.86 Safari/537.36

  • Response

    • Status : 200 ( OK )

    • Headers

      • Access-Control-Allow-Credentials : true
      • Access-Control-Allow-Origin : *
      • Connection : keep-alive
      • Content-Length : 34
      • Content-Type : application/json
      • Server : nginx

    • Body

      {
  "origin": "[ your ip address ]"
}

References