Less specific 404 takes precendence over more specific 405 when serveDirectory is used

[sol]

Given the following API

type MyAPI = "run" :> Post '[JSON] () :<|> Raw

server :: Server MyAPI
server = liftIO runJob :<|> serveDirectory "static"

doing a GET request to /run will result in a 404 instead of the desired 405.

I assume this is because we try handlers in order until we get something different from 4xx. I'm also not sure what's the right way to fix this, so I'm mainly leaving this here to get more input.

[sol]

One way to fix this could be to have some ordering (from less specific to more specific) over 4xx errors, and then always return the most specific error. 404 would then be at the beginning of the list.

[fizruk]

@sol I don't think it is a good idea to run multiple endpoints that match the same path.
Note that it is possible that 4xx error is thrown halfway through the application logic.

In my opinion a better approach would be to isolate Raw in a subpath, e.g. "static" :> Raw.

In any case, in master there already exists an ordering of 4xx error.
But it only happens when routing is being done, that is when servant combinators are being processed. But since Raw handles routing in the application code, servant can't put it into routing.

It might be possible, however, to create a new StaticDir combinator, which would separate routing part of serveDirectory and allow for better error fallbacks.

[jkarni]

Yeah, Raw is the problem. We could perhaps make an exception type that Raw could throw to indicate routing status, but even then most Applications wouldn't work out of the box.

[jkarni]

While the situation isn't great, I don't think there's anything we can really do about it. Can I close this?

[kosmikus]

@jkarni There should be an open issue that we need to move away from Raw for serving static files if possible. Is there already?

[3noch]

This is related: #350

[jkarni]

Closing in favour of #507