This is where I got the implementation from.

What's the relationship between this and formParam(s) ?

If the only difference is which form encoding they can handle, we might want to extend the current functions rather than introducing a new one.

formData could be rewritten in terms of formParams, Form and fromForm.

Which shows that yes, it is basically just support for a new encoding.

I initially added this because it was mentioned in #321 but I don't personally think that this is important functionality...

Does body preserve the request body across calls to next? see #308

I'm not 100% sure what the desired behavior is, I assumed this was "right" because of the way jsonData is written :)

Should I add a test here?

Internally, both formParams and formData use getBodyAction which I believe leads to consistent behavior unless I'm missing something.

Correct! (beautiful diagram btw, how did you make it?)

Basically this "lazier" parsing of request bodies (underneath the implementation of files, formParams etc.) is what I introduced in #369 and I think it would make sense for form parameters too.

The diagram is made using plant UML, basically a text-based UML tool. Getting the call graph from Haskell isn't automatic tho, I did that by hand. Below is the source code for it.

@startuml
skinparam dpi 300

hide members
hide circle

package "Web.Scotty.Action" {
    formParams -down-> "Web.Scotty.Internal.Types.formParamsAndFilesWith"
    formData -down-> body
    body -down-> "Web.Scotty.Internal.Types.envBody"
}

package "Web.Scotty.Internal.Types" {
    formParamsAndFilesWith -left-> envFormDataAction
    envFormDataAction -down-> "Web.Scotty.Body.getFormParamsAndFilesAction"
    envBody -down-> Web.Scotty.Body.getBodyAction
}

note top of Web.Scotty.Internal.Types.envFormDataAction
Initialized by mkEnv
end note

note top of Web.Scotty.Internal.Types.envBody
Initialized by mkEnv
end note

package "Web.Scotty.Body" {
    getFormParamsAndFilesAction -down-> getBodyAction
    getFormParamsAndFilesAction -right-> parseRequestBodyExBS
    parseRequestBodyExBS -down-> "Network.Wai.Parse.sinkRequestBodyEx"
}

package "Network.Wai.Parse" {
    sinkRequestBodyEx -down-> conduitRequestBodyEx
    conduitRequestBodyEx -down-> "Network.HTTP.Types.parseSimpleQuery"
}

package Network.HTTP.Types {
    parseSimpleQuery -right-> parseQuery
    parseQuery -right-> urlDecode
}
@enduml