As we known, standard httprouter func has 3 parameters like below:

func ViewIndex(w http.ResponseWriter, r *http.Request, ps httprouter.Params){}

Sometimes, we need pass additional arguments to httprouter handle func, like:

func ViewIndex(w http.ResponseWriter, r *http.Request, ps httprouter.Params, settings map[string]string){}

There are two ways to achive this target:

1. Use a wrapper

   func getIndexWithSettings2(s Settings) httprouter.Handle {
   return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
       // Settings is in the scope and ps httprouter.params
       fmt.Println(s.Path)
   }
   }

2. Use a middleware

   func settingsMiddleware(h http.Handler) http.Handler {
   return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
       // Take the context out from the request
       ctx := r.Context()
   
       // Get the settings
       s := somewhere()
   
       // Get new context with key-value "settings"
       ctx = context.WithValue(ctx, "params", s)
   
       // Get new http.Request with the new context
       r = r.WithContext(ctx)
   
       // Call your original http.Handler
       h.ServeHTTP(w, r)
   })
   }

Full example

package main

import (
    "context"
    "fmt"
    "net/http"
    "github.com/julienschmidt/httprouter"
)

func main() {
    r := httprouter.New()
    index := settingsMiddleware(http.HandlerFunc(getIndex))
    r.GET("/index", wrapHandler(index))
    http.ListenAndServe(":8080", r)
}

func wrapHandler(h http.Handler) httprouter.Handle {
    return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
        // Take the context out from the request
        ctx := r.Context()
        ctx = context.WithValue(ctx, "params", ps)
        r = r.WithContext(ctx)
        h.ServeHTTP(w, r)
    }
}

func settingsMiddleware(h http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        var s = "/var/bin"

        ctx := r.Context()
        ctx = context.WithValue(ctx, "settings", s)
        r = r.WithContext(ctx)
        h.ServeHTTP(w, r)
    })
}

func getIndex(w http.ResponseWriter, r *http.Request) {
    s, ok := r.Context().Value("settings").(string)

    if !ok {
        fmt.Println("s is not type string")
    }

    fmt.Println(s) // "/var/bin"
}