Question

I’m designing an API to go over HTTP and I am wondering if using the HTTP POST command, but with URL query parameters only and no request body, is a good way to go.

Considerations:

• "Good Web design" requires non-idempotent actions to be sent via POST. This is a non-idempotent action.
• It is easier to develop and debug this app when the request parameters are present in the URL.
• The API is not intended for widespread use.
• It seems like making a POST request with no body will take a bit more work, e.g. a Content-Length: 0 header must be explicitly added.
• It also seems to me that a POST with no body is a bit counter to most developer’s and HTTP frameworks’ expectations.

Are there any more pitfalls or advantages to sending parameters on a POST request via the URL query rather than the request body?

Edit: The reason this is under consideration is that the operations are not idempotent and have side effects other than retrieval. See the HTTP spec:

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.

…

Methods can also have the property of "idempotence" in that (aside from error or expiration issues) the side-effects of N > 0 identical requests is the same as for a single request. The methods GET, HEAD, PUT and DELETE share this property. Also, the methods OPTIONS and TRACE SHOULD NOT have side effects, and so are inherently idempotent.

Answer 1

If your action is not idempotent, then you MUST use POST. If you don’t, you’re just asking for trouble down the line. GET, PUT and DELETE methods are required to be idempotent. Imagine what would happen in your application if the client was pre-fetching every possible GET request for your service – if this would cause side effects visible to the client, then something’s wrong.

I agree that sending a POST with a query string but without a body seems odd, but I think it can be appropriate in some situations.

Think of the query part of a URL as a command to the resource to limit the scope of the current request. Typically, query strings are used to sort or filter a GET request (like ?page=1&sort=title) but I suppose it makes sense on a POST to also limit the scope (perhaps like ?action=delete&id=5).