I'm learning how to design a RESTful API and I've come across a quandary.
Say I have a POST endpoint to perform an action. The action has a certain cost associated with it. The cost depends on what the action is, particularly, on the body of the POST. For example, given these two requests:
POST /flooblinate
{"intensity": 50, "colorful": true, "blargs": [{"norg": 43}]}
POST /flooblinate
{"intensity": 100, "colorful": false, "blargs": []}
Say the first one costs 500 and the second one costs 740.
I want to create a method which will tell me what the cost of posting the action will be. Since I am not creating or updating anything, it seems that GET is the most appropriate verb. However, a request body with GET should not have any meaning. This means that I'd have to put the data in the query string, say by URL encoding the request body to be passed to the POST:
GET /flooblinate/getCost?body=%7B%22intensity%22%3A+50%2C+%22colorful%22%3A+true%2C+%22blargs%22%3A+%5B%7B%22norg%22%3A+43%7D%5D%7D
This seems less than ideal since it's two data formats for the same thing. But the following:
POST /flooblinate/getCost
{"intensity": 50, "colorful": true, "blargs": [{"norg": 43}]}
This also seems less than ideal since it's abusing the POST verb to query information, instead of to create or update something.
What's the correct choice to make, here? Is there any third alternative? Is there a way to rethink this design fundamentally which will obviate the need to make this choice?