HTTP 405 Method Not Allowed about httprouter

[julienschmidt]

Originally each leaf in the radix tree contained a map mapping the request methods to handler functions. This would have allowed to easily return all allowed methods and was actually a planned feature: https://github.com/julienschmidt/httprouter/blob/v1/tree.go#L327

But it is usually a lot more efficient and especially a lot more memory efficient to manage distinct trees per request methods. In the current version the router contains a map mapping request methods to the respective radix tree. So we do the map lookup first and then walk the tree to find the handler function.
This has the disadvantage that the allowed methods can not easily be returned. We had to walk every single tree first and check if a handler is registered. Alternatively we could maintain another structure to check this with a single lookup.

This is definitely a feature I would like to implement someday, but currently there is no plan when or how this should happen.