It is important to remember that an HTTP response completes the HTTP transaction. Many people new to Web development have a difficult time distinguishing between server-side code (code that executes on the server) and client-side code (code that executes on the client). Scripting languages such as PHP, ColdFusion, and JSP are executed on the server, and their output is included in the HTTP response. In fact, their output is the content of the HTTP response, and most modern Web scripting languages also allow for some manipulation of the HTTP as well, such as altering or adding headers, changing status codes, and so on. Once the Web client receives the HTTP response, the transaction is complete. The Web client will then render the page, execute client-side scripts such as JavaScript, load images (by issuing separate GET requests), and so on.

With HTTP/1.1, persistent connections are the default behavior. This means that the Web server will not close the connection after sending the HTTP response unless the client intends to close the connection after receiving it. In this case, the client will include the following header in the HTTP request:

Connection: close 

Alternatively, the server can close the connection upon sending the HTTP response, although it should be polite and include the same header as shown previously so that the Web client expects this action.

An HTTP response is broken into the following three logical pieces:

• Status line

• HTTP headers

• Content

An example status line is as follows:

HTTP/1.1 200 OK 

The status line contains three elements:

• The version of HTTP being used, in the format HTTP/x.x

• The status code

• A short description of the status code

There are three types of HTTP headers allowed in a response:

• General headers

• Response headers

• Entity headers

Status codes are grouped into the following ranges:

• Informational (100-199)

• Successful (200-299)

• Redirection (300-399)

• Client error (400-499)

• Server error (500-599)

• 100 Continue
• 101 Switching Protocols
• 200 OK
• 400 Bad Request
• 401 Unauthorized
• 403 Forbidden
• 404 Not Found
• 500 Internal Server Error
• 502 Bad Gateway
• 503 Service Unavailable

Content-Disposition, combined with a proper Content-Type header, provides the developer absolute control over the interpretation of the resource's media type.