HTTP Protocol

HTTP Features

  • Persistent Connection (HTTP/1.1): TCP connection is maintained without explicit disconnection
    • Both server and client must support it
    • Uses keep-alive header
  • Pipelining: When multiple requests are needed, send all requests before receiving responses (useful for loading scripts and images in HTML documents)
  • Range Request: Partial download for resume functionality
  • Content Negotiation
    • Server-driven negotiation
    • Agent-driven negotiation (user decides)
    • Transparent negotiation (mix of both)

HTTP Request

HTTP Methods

  • GET: Retrieve resource
  • POST: Send entity
  • PUT: Transfer file
  • HEAD: Get message headers only
  • DELETE: Delete file
  • OPTIONS: Query available methods
  • TRACE: Trace route
  • CONNECT: Request tunneling from proxy

Request Message Structure

Components: Method, URI, Protocol Version, Request Headers, Entity

POST /form/entry HTTP/1.1
Host: hackr.jp
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 16

name=ueno&age=37

GET /index.html HTTP/1.1
Host: www.hackr.jp

POST Method Content Types (MIME types)

multipart/form-data

  • Use when you have binary (non-alphanumeric) data or a significantly sized payload
  • Has overhead for short alphanumeric values

application/x-www-form-urlencoded

  • Use for regular form data
  • Not suitable for byte values
  • Reserved and non-alphanumeric characters are replaced by %HH (percent sign and two hexadecimal digits representing the ASCII code)
  • This can triple the size for binary data

HTTP Response

Response Message Structure

Components: Protocol Version, Status Code, Status Description, Response Headers, Body

HTTP/1.1 200 OK
Date: Tue, 10 Jul 2012 06:50:15 GMT
Content-Length: 362
Content-Type: text/html

<html>
...

Common Status Codes

  • 200 OK: Request succeeded
  • 400 Bad Request: Invalid request

Curl - API Testing Tool

Basic Usage

curl http://localhost:9091/messagePattern

Options

  • -G: GET request
  • -v: Verbose output
  • --data-urlencode: Encode query parameters

Examples

Basic Authentication

curl --user daniel:secret http://example.com/

URL Encoding

curl -G -v http://localhost:3000/ --data-urlencode "query=word"
# Results in: http://localhost:3000/?query=word