Extract request utilities into its own package

The RemoteAddr and RemoteIP functions operate on *http.Request values,
not contexts. They have very low cohesion with the rest of the package.

Signed-off-by: Cory Snider <csnider@mirantis.com>

internal/dcontext/http.go

@@ -3,15 +3,14 @@ package dcontext
 import (
 	"context"
 	"errors"
-	"net"
 	"net/http"
 	"strings"
 	"sync"
 	"time"
 
+	"github.com/distribution/distribution/v3/internal/requestutil"
 	"github.com/google/uuid"
 	"github.com/gorilla/mux"
-	log "github.com/sirupsen/logrus"
 )
 
 // Common errors used with this package.
@@ -20,48 +19,6 @@ var (
 	ErrNoResponseWriterContext = errors.New("no http response in context")
 )
 
-func parseIP(ipStr string) net.IP {
-	ip := net.ParseIP(ipStr)
-	if ip == nil {
-		log.Warnf("invalid remote IP address: %q", ipStr)
-	}
-	return ip
-}
-
-// RemoteAddr extracts the remote address of the request, taking into
-// account proxy headers.
-func RemoteAddr(r *http.Request) string {
-	if prior := r.Header.Get("X-Forwarded-For"); prior != "" {
-		remoteAddr, _, _ := strings.Cut(prior, ",")
-		remoteAddr = strings.Trim(remoteAddr, " ")
-		if parseIP(remoteAddr) != nil {
-			return remoteAddr
-		}
-	}
-	// X-Real-Ip is less supported, but worth checking in the
-	// absence of X-Forwarded-For
-	if realIP := r.Header.Get("X-Real-Ip"); realIP != "" {
-		if parseIP(realIP) != nil {
-			return realIP
-		}
-	}
-
-	return r.RemoteAddr
-}
-
-// RemoteIP extracts the remote IP of the request, taking into
-// account proxy headers.
-func RemoteIP(r *http.Request) string {
-	addr := RemoteAddr(r)
-
-	// Try parsing it as "IP:port"
-	if ip, _, err := net.SplitHostPort(addr); err == nil {
-		return ip
-	}
-
-	return addr
-}
-
 // WithRequest places the request on the context. The context of the request
 // is assigned a unique id, available at "http.request.id". The request itself
 // is available at "http.request". Other common attributes are available under
@@ -193,7 +150,7 @@ func (ctx *httpRequestContext) Value(key interface{}) interface{} {
 		case "http.request.uri":
 			return ctx.r.RequestURI
 		case "http.request.remoteaddr":
-			return RemoteAddr(ctx.r)
+			return requestutil.RemoteAddr(ctx.r)
 		case "http.request.method":
 			return ctx.r.Method
 		case "http.request.host":