HTTP

Hypertext Transfer Protocol

    Resumo/Informações HTTP - Hypertext Transfer Protocol
    • Identifying Resources on the Web
      • Based on the Request/Response protocol.
      1) Cliente abre uma conexão com o servidor.
      2) Cliente envia HTTP request sobre um recurso.
      3) O servidor envia uma resposta HTTP para o cliente (com o recurso).
      4) O cliente fecha a conexão com o servidor.
      5) Caso o recurso não é encontrado um erro ocorre.

    • URN: Uniform Resource Name
      •   * Uniquely identifies resourse or name of resource.
        * Does not tell us how to get the resourse.
        Ex: HTML/CSS/javascript/Web Developers/Yaakov/Chaikin seria um link único utilizado pelo Coursera para identificar esse curso dentro do site.

    • URI: Uniform Resource Identifier
      •   * Uniquely identifies resource or location of resource.
        * Does not necessarily tell us how to get the resource.
        Ex: /official_web_site/index.html - this url alone doesn't say where you can find this.

    • URL: Uniform Resource Locator
      •  * Form of URI that provides info on how to get resource.
       Ex: http://mysite.co.uk/index.html

       * URN & URI: uniforms a resource identification, but does not provides its location.
       * URL: provides a identification that directly sends you to the location of the resource.

        Resumo:
        1. Client connects with the server of mysite.co.uk.
        2. The HTTP gets in action, being the comunication language between the client and server.

      HTTP Methods
    • Request Stucture
      • GET:
        * Retrieves the resource.
        * Data is passed to server as part of the URI. Passa a data para o server como parte da URL.
      Ex: GET / index.html?firstName=Diego HTTP/1.1
      Get: method
      index.html: URI String
      ?firstName=Diego: Query String (name/value pairs separeted by & examble: ?first=Diego&last=M.)
      HTTP/1.1: HTTP Version

      POST:
        * Sends data to server to be processed.
        * Data is sent in the message body. Envia dados como parte da mensagem no body.
      Ex: POST / index.html HTTP/1.1
      Host: coursera.org       \ Request
      Accept-Charset: utf-8 / Headers
      firstName=Diego...      - Message body starts here
      ...

    • Response Stucture
      • HTTP/1.1 - HTTP Version
      200 - Response status code
      OK - English phrase describing status code
      Content-Type: text/html
      HTML content here - Aqui pode ser jSon, entre outros.
      ...
      ...

    • Examples: Response Status Codes - STATUS
      • * 200 OK - OK, here is the content you requested. :)
      * 404 NOT FOUND - Server can't find the resource requested.
      * 403 FORBIDDEN - Unauthenticated client tried to access a secure resource.
      * 500 INTERNAL SERVER ERROR - Some unhandled error was raised on the server.

      Onreadystatechange: allows an event to happen at every state change. Permite disparar um evento a cada mudança de status (abaixo).

      readyState - STATES
      0 - UNSENT - Object not initiated, open() method still wasn't called.
      1 - OPENED - Loading data, send() method still wasn't called.
      2 - HEADERS_RECEIVED - Data loaded, send() method still wasn't called but the head responses were recieved.
      3 - LOADING - Modo interativo, the response is being recieved.
      4 - DONE - Operation completed. What was requested already got it's answer