Giraffe.SerilogExtensions

Dead simple library to integrate Serilog within Giraffe or Saturn apps: implemented as a composable HttpHandler and has native destructuring of F# types. No need to involve the dependency injection mechanism to get the logger up and running.

Install

dotnet add package Giraffe.SerilogExtensions

Usage

Wrap an existing HttpHandler with SerilogAdapter.Enable and you are done!

open Giraffe
open Giraffe.SerilogExtensions
open Serilog 

// your application
let webApp = GET >=> route "/" >=> text "Home"

// Enable logging on an exisiting HttpHandler 
let webAppWithLogging = SerilogAdapter.Enable(webApp)

// Configure Serilog: sinks and enrichers go here
Log.Logger <- 
  LoggerConfiguration()
    // add native destructuring
    .Destructure.FSharpTypes()
    // from Serilog.Sinks.Console
    .WriteTo.Console() 
    .CreateLogger() 

(* configure Giraffe to run here... *)

Now dotnet run and curl http://localhost:8080 to get the following logs:

[20:35:42 INF] GET Request at /
[20:35:42 INF] GET Response (StatusCode 200) at / took 121 ms

These request and response log events contain many properties that are extracted from the HttpContext, enable a detailed console sink with JsonFormatter to see what properties are extracted from the http context:

open Serilog.Formatting.Json
(*
  ...
*)
Log.Logger <- 
  LoggerConfiguration()
    .Destructure.FSharpTypes()
    .WriteTo.Console() // from Serilog.Sinks.Console
    .WriteTo.Console(JsonFormatter())
    .CreateLogger() 

Now there logs become as follows, since there are two sinks, one is normal console log and the other is detailed LogEvent in JSON format, you can tell from the headers that I am using Postman for testing.

[19:43:12 INF] GET Request at /index
{"Timestamp":"2018-12-22T19:43:12.5837113+01:00","Level":"Information","MessageTemplate":"{Method} Request at {Path}","Properties":{"RequestId":"2b47246b-ba4f-4b24-9d12-fe1827fcfa87","Type":"Request","Path":"/index","Method":"GET","Host":"localhost","Port":5000,"Query":{},"RequestHeaders":{"Accept":"*/*","Accept-Encoding":"gzip, deflate","Cache-Control":"no-cache","Connection":"keep-alive","Host":"localhost:5000","Postman-Token":"61f5470e-27ad-4a98-b074-c7e41bceb1f7","User-Agent":"PostmanRuntime/7.4.0"},"UserAgent":"PostmanRuntime/7.4.0","Body":"","ContentType":""}}

[19:43:12 INF] GET Response (StatusCode 200) at /index took 163 ms
{"Timestamp":"2018-12-22T19:43:12.7419652+01:00","Level":"Information","MessageTemplate":"{Method} Response (StatusCode {StatusCode}) at {Path} took {Duration} ms","Properties":{"Duration":163,"Path":"/index","RequestId":"2b47246b-ba4f-4b24-9d12-fe1827fcfa87","Type":"Response","Method":"GET","StatusCode":200,"ContentType":"text/plain; charset=utf-8"}}

Logs from the same roundtrip will include a RequestId property that is the same for these logs to trace them back using your favorite log server.

Use the logger from inside the HttpHandler

You can get a reference for a logger with the RequestId attached to it from inside a HttpHandler:

let webApp = 
  choose [ GET >=> route "/" >=> text "Home"
           GET >=> route "/index" 
               >=> context (fun ctx ->
                     // get the contextual logger
                     let logger = ctx.Logger() 
                     logger.Information("Read my {RequestId}")
                     text "Some response") ]

the Logger() method is an extension method to HttpContext. The context combinator is another handy extension from this library that allows access to the current HttpContext from which you create a new HttpHandler.

Ignore log fields

As you can see, there many fields being logged from the request and response. You can configure the logger to ignore some fields:

let serilogConfig = 
  { SerilogConfig.defaults with
      IgnoredRequestFields = 
        Ignore.fromRequest
        |> Field.host
        |> Field.queryString
      IgnoredResponseFields = 
        Ignore.fromResponse
        |> Field.contentType }

let webAppWithLogging = SerilogAdapter.Enable(webApp, serilogConfig)

Error Handling

Error handling within the Serilog HttpHandler is also handled by Serilog and not Giraffes's internal logger. The error handler is of type: Exception -> HttpContext -> HttpHandler with the default handler returning a generic error message from the server:

let errorHandler ex httpContext = 
    setStatusCode 500 
    >=> text "Internal Server Error" 

You can override this error handler from the config:

let serilogConfig = 
 { SerilogConfig.defaults with 
    ErrorHandler = 
      fun ex httpContext -> 
        // NancyFx-style apologetic message :D
        setStatusCode 500 
        >=> text "Sorry, something went terribly wrong!" }

let webAppWithLogging = SerilogAdapter.Enable(webApp, serilogConfig)

Builds

Building

Make sure the following requirements are installed in your system:

• dotnet SDK 6.0 or higher

cd ./build
dotnet run

Run Tests

cd ./build
dotnet run -- test