Question

In ASP.NET MVC it seems to be common practice not to use GET requests for calls to a controller that modify the model. For example, deleting a customer should not be possible by clicking a simple HTML link.

The only reason for this rule I am aware of is not safeguard against web-crawlers which might indavertently alter the database. GET requests are commonly regarded as safe, whereas POST requests are not.

Does this mean that this rule does not apply to non-public portions of a website (Example: Your password-protected user administration area)? Or is there any other reason not to use destructive GET requests?

Answer 1

This is generally part of HTTP. From the HTTP 1.1 RFC 2616

Implementors should be aware that the software represents the user in their interactions over the Internet, and should be careful to allow the user to be aware of any actions they might take which may have an unexpected significance to themselves or others.

In particular, the convention has been established that the GET and HEAD methods SHOULD NOT have the significance of taking an action other than retrieval. These methods ought to be considered ‘safe’. This allows user agents to represent other methods, such as POST, PUT and DELETE, in a special way, so that the user is made aware of the fact that a possibly unsafe action is being requested.

Naturally, it is not possible to ensure that the server does not generate side-effects as a result of performing a GET request; in fact, some dynamic resources consider that a feature. The important distinction here is that the user did not request the side-effects, so therefore cannot be held accountable for them.

In other words, it’s not enforced, but it’s really bad form for a GET request to have side-effects. Imagine if a user bookmarks a URL which does updates something, for example – they probably wouldn’t expect that to happen.