Allow access to URL path in a more manageable format

[KaneTW]

I'm currently writing an implementation of rate limiting for servant-client, and it'd be very useful to have access to the current URL path as e.g. a [PathPiece] where

data PathPiece
  = StaticPath Text
  | Capture String Text

so that I can properly group rate limiting bins by specific Captures.

Ideally, I'd be able to do something like

type RateLimitedAPI = "foo" :> "bar" :> Capture "id" Int :> Capture "minor" Int :> RateLimit (IgnoreCapture "minor") :> Post '[JSON] Foo

[phadej]

why you don't put RateLimit before "minor" capture and treat it as all api endpoints share this rate limiter?

EDIT which might be good idea, as I don't recall too many API with granular per-resource rate limiting.

[KaneTW]

I need /foo/bar/:id/:minor to be a distinct bin than /foo/bar/:id.

[phadej]

let me think a bit.

• I'm very hesitant to change PathPiece
• you'd rather want to know the bin at compile time, from what's before RateLimit
• and with #856 one could write Capture' '[RateLimiterIgnored] "minor" :> RateLimit :> ...
• but I don't know (yet) how to write instance for RateLimit in this setting

[phadej]

For now, I'd suggest to name the bins explicitly: RateLimit "/foo/bar/:id".

[KaneTW]

I'll probably go for something like

type RateLimitedAPI = "foo" :> "bar" :> Capture "id" Int :> RateLimit "minor" :> Capture "minor" Int :> Post '[JSON] Foo

and use the currently constructed Request path + the type-level symbol as a bin.

[KaneTW]

Humm. I need to query my MonadRateLimit whether a request can be performed or not, but

• I can't perform actions
• Request has no field for user data

I can use a custom header and populate it with the bin name, for now, but it's not particularly elegant.