[ASP.NET] Web Application Components

Web applications consist of several components: servers, browsers, and communication protocols. You can decide different technologies and products for servers and browsers. But you need to use HTTP as a basic communication protocol.

ASP.NET is a server technology. Most works are done in a server and the result HTML will send to a client’s browser. ASP.NET server controls do their best to show the result similar across all browsers.

This post is not specific to ASP.NET. All web programming models share the common components.  

1. Web Servers

The web server is responsible for accepting requests for a resource and sending the appropriate response.

  • Stateless: process GET request, send response, and close server connection
  • State: process GET request, execute server-side code, store session data, and send response

2.  Web Browsers

The web browser is responsible for displaying data to a user, collecting data from a user, and sending data to the web server.

  • Add-on Technologies: JavaScript, AJAX, MS Silverlight, and plug-ins

3. HTTP

HTTP (Hypertext Transfer Protocol) is a text-based communication protocol that is used to communicate between web browsers and web servers using port 80. “Secure HTTP (HTTPS)” uses port 443.

Each HTTP command contains a method (also called a verb) that indicates the desired action.

  • GET: used to obtain a web resource, usually in a read only fashion
  • POST: used to send data to a web server
  • HEAD: equivalent to GET except that it only returns meta-information of the resource
  • OPTIONS: lists which of the seven methods can be executed against a target resource
  • TRACE: is for debugging purposes and reflects a client request back from the server to the client to check how it might have changed en route
  • PUT: places a resource at the URL that is the target of the HTTP request
  • DELETE: removes the resource from the URL

HTTP methods can be grouped:

  • Safe methods: GET, OPTIONS, HEAD, and TRACE
  • Unsafe methods: PUT, DELETE, and POST

The idempotent method means that if you execute them more than once, the result is the same as executing them only once. POST is the only one that is NOT considered “idempotent.”

4. DAV

Distributed Authoring and Versioning (DAV) is a set of extensions to HTTP/1.1 that simplifies Web development when working in a team scenario.

  • DAV provides more methods such as LOCK/UNLOCK files
  • DAV directly built on HTTP, so no other protocols required

5. HTTP Status Code

  • 1xx:  Informational
  • 2xx: Success
  • 3xx: Redirect
  • 4xx: Client Error
  • 5xx: Server Error
(examples) 
100: Continue

200: OK 
201: Created

300: Multiple Choices
301: Moved Permanently

400: Bad Request
401: Unauthorized
403: Forbidden
404: Not Foundbr
407: Proxy Authentication Required
408: Request Time-out

500: Internal Server Error
501: Not Implemented

6. Postback

Sending data back to the same page in the server from the browser is referred to as a Postback. It is the basic method to send data to a server in ASP.NET.

<form id="form1" runat="server">
    Enter Customer ID: <input type=”text” id=”Id” runat="server" />
    <input type=”submit” runat="server" value=”Get Customer” />
</form>

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