context_middleware_chain.go

package gocontext

import (
	"context"
	"net/http"
)

type SomeMiddleware interface {
	HandleHTTPC(ctx context.Context, rw http.ResponseWriter, req *http.Request, next http.Handler)
}

var functionA SomeMiddleware = nil
var functionB SomeMiddleware = nil

func addUserID(rw http.ResponseWriter, req *http.Request, next http.Handler) {
	ctx := context.WithValue(req.Context(), "userid", req.Header.Get("userid"))
	req = req.WithContext(ctx)
	next.ServeHTTP(rw, req)
}

func useUserID(rw http.ResponseWriter, req *http.Request, next http.Handler) {
	uid := req.Context().Value("userid")
	rw.Write([]byte(uid))
}

func makeChain(chain ...SomeMiddleware) http.Handler {return nil}

type Server struct {}

func (s *Server) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
	req = req.WithContext(context.Background())
	chain := makeChain(addUserID, functionA, functionB, useUserID)
	chain.ServeHTTP(rw, req)
}