Brief about HTTP Transaction? | ASP.Net Web API Interview Question | ASP.Net Web API Programmer Guide


HTTP is an application layer protocol based on a reliable transport layer protocol (read TCP). The two endpoints of the communication based on HTTP are a server and a client. The client sends a request to the server; the server processes the request and sends a response back to the client that includes a status code denoting if the processing is successful or not. These steps constitute an HTTP transaction. The client typically is a web browser such as Internet Explorer, and the server is a web server such as IIS. A web server services multiple clients simultaneously. The HTTP client initiates an HTTP request by connecting to a port (typically 80) on the web server.
Web servers host resources that are uniquely identified through an identifier called the Uniform Resource Identifier (URI). The Uniform Resource Locator (URL) is a URI—it identifies a resource but it also specifies how a representation of a resource can be obtained. For example, is a URL that includes three parts.
  1.  Scheme, which is http://. The scheme denotes the protocol used (HTTP).
  2. Server, which is The server is the server that hosts the resource.
  3. Resource path, which is /home.html. The resource path is the path of the resource on the server.

A client requests the server to take an action on a resource. There is a noun and a verb associated with the request. The noun is the resource identified by the URI. The verb is the action or the HTTP method. In the above figure, the client requests GET on /home.html. The server responds with a 200 OK status code and sends the text/html representation of the resource. The server specifies the representation (text/html) in the Content-Type response header. The content type is also called the media type.