tour - touring some programming systems

package main

import (
	"context"
	"log"
	"net"
	"net/http"
	"strings"
)

// Attaches a request's IP address to the request's context.
// If getwtxt is behind a reverse proxy, get the last entry
// in the X-Forwarded-For or X-Real-IP HTTP header as the user IP.
func newCtxUserIP(ctx context.Context, r *http.Request) context.Context {

	base := strings.Split(r.RemoteAddr, ":")
	uip := base[0]

	if _, ok := r.Header["X-Forwarded-For"]; ok {
		proxied := r.Header["X-Forwarded-For"]
		base = strings.Split(proxied[len(proxied)-1], ":")
		uip = base[0]
	}

	xRealIP := http.CanonicalHeaderKey("X-Real-IP")
	if _, ok := r.Header[xRealIP]; ok {
		proxied := r.Header[xRealIP]
		base = strings.Split(proxied[len(proxied)-1], ":")
		uip = base[0]
	}

	return context.WithValue(ctx, ctxKey, uip)
}

// Retrieves a request's IP address from the request's context
func getIPFromCtx(ctx context.Context) net.IP {

	uip, ok := ctx.Value(ctxKey).(string)
	if !ok {
		log.Printf("Couldn't retrieve IP from request\n")
	}

	return net.ParseIP(uip)
}

// Shim function to modify/pass context value to a handler
func ipMiddleware(hop http.Handler) http.Handler {

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		ctx := newCtxUserIP(r.Context(), r)
		hop.ServeHTTP(w, r.WithContext(ctx))
	})
}

func log200(r *http.Request) {

	uip := getIPFromCtx(r.Context())
	log.Printf("*** %v :: 200 :: %v %v\n", uip, r.Method, r.URL)
}

func log400(w http.ResponseWriter, r *http.Request, err string) {
	uip := getIPFromCtx(r.Context())
	log.Printf("*** %v :: 400 :: %v %v :: %v\n", uip, r.Method, r.URL, err)
	http.Error(w, "400 Bad Request: "+err, http.StatusBadRequest)
}

func log404(w http.ResponseWriter, r *http.Request, err error) {

	uip := getIPFromCtx(r.Context())
	log.Printf("*** %v :: 404 :: %v %v :: %v\n", uip, r.Method, r.URL, err)
	http.Error(w, err.Error(), http.StatusNotFound)
}

func log500(w http.ResponseWriter, r *http.Request, err error) {

	uip := getIPFromCtx(r.Context())
	log.Printf("*** %v :: 500 :: %v %v :: %v\n", uip, r.Method, r.URL, err)
	http.Error(w, err.Error(), http.StatusInternalServerError)
}


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