assigning to an http request in a handler

[zilto karamazov]

Hello,

I'm wondering if it is ok to do this ?

////

package main

import (
        "context"
        "fmt"
        "log"
        "net/http"

        "github.com/gorilla/mux"
)

func main() {
        addr := "127.0.0.1:8080"
        r := mux.NewRouter()

        r.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
                newReq := r.WithContext(context.WithValue(r.Context(), 0, "bla"))
                *r = *newReq
                // set context
        })

        r.Use(func(next http.Handler) http.Handler {
                return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
                        next.ServeHTTP(w, r)

                        ctx := r.Context()
                        v, ok := ctx.Value(0).(string)
                        if !ok {
                                fmt.Println("could not find context value")
                        } else {
                                fmt.Println(v)
                        }
                })
        })

        s := &http.Server{
                Addr:    addr,
                Handler: r,
        }

        if err := s.ListenAndServe(); err != nil && err != http.ErrServerClosed {
                log.Fatalf("could not listen on %s : %v", addr, err)
        }
}
////

[Uli Kunitz]

I don't think this is a good idea.

I would do something like this.

type mykey struct{}

var key mykey

r.Use(func(next http.Handler) http.Handler {
                return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {

                        var s string

                        r = r.WithContext(context.WithValue(r.Context(), &key, &s))

                        next.ServeHTTP(w, r)

                        if s != "" {

                                    fmt.Fprint("string %s\n", s)

                        }                      

                })
        })

In the handler itself you must of course get the value by assuming that key will always have string pointer. You can then assign a string to the pointer, which will be output if its non-nil. Wonder whether you want to store a map or a io.Writer as value instead of a single string.

[Uli Kunitz]

It should be 

r = r.WithContext(context.WithValue(r.Context(), key, &s))

Using the address of a key was a typo.

[Amit Saha]

What is the goal you are trying to accomplish here?