How to customize logging in F# Saturn framework? - f#

Question

I created a default SAFE app as described here.
Removing redundant stuff, the server is this:
open Giraffe
open Saturn
let webApp = scope {
get "/api/init" (fun next ctx ->
task {
let number = 42
let! counter = task { return number }
return! Successful.OK counter next ctx
})
}
let app = application {
url ("http://0.0.0.0:8085/")
router webApp
memory_cache
use_static "../Client/public"
use_gzip
}
run app
Now, when running app, I see some logging in the console, basically incoming requests:
info: Microsoft.AspNetCore.Hosting.Internal.WebHost[1]
Request starting HTTP/1.1 GET http://localhost:8085/api/init
How do I customize the logging? The docs are as scarce as possible, no examples. I need something simple, like logging "going to return 42...".
Or at least some links with cases.

Answer 1

You can pull the fully blown ILogger object from the context, ctx.
Open Microsoft.Extensions.Logging module and then you can do things like this:
let webApp = scope {
get "/api/init" (fun next ctx ->
task {
let logger = ctx.GetLogger();
let number = 42
logger.Log(LogLevel.Information, "Going to return " + number.ToString())
let! counter = task { return number }
return! Successful.OK counter next ctx
})
}
This will bring to your console:
info: object[0]
Going to return 42
I do not have any proper references. I found a similar thing at the Github of Giraffe server for which Saturn is basically a set of abstractions.

Answer 2

Logging configuration is built into v0.9 at least. I used the case below for myself to suppress most of the logging.
open Microsoft.Extensions.Logging
let app = application {
url ("http://0.0.0.0:8085/")
use_router webApp
logging (fun logger -> logger.SetMinimumLevel LogLevel.Critical |> ignore)
}