net/http: make use of maps.Copy

Change-Id: If8e02760fe1fb095ecebc306fd98662a51a1f66f
GitHub-Last-Rev: 7b8099f1fe
GitHub-Pull-Request: golang/go#69426
Reviewed-on: https://go-review.googlesource.com/c/go/+/612736
Reviewed-by: Tim King <taking@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/net/http/server.go

@@ -3683,9 +3683,7 @@ func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
 		tw.mu.Lock()
 		defer tw.mu.Unlock()
 		dst := w.Header()
-		for k, vv := range tw.h {
-			dst[k] = vv
-		}
+		maps.Copy(dst, tw.h)
 		if !tw.wroteHeader {
 			tw.code = StatusOK
 		}

src/net/http/transfer.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"internal/godebug"
 	"io"
+	"maps"
 	"net/http/httptrace"
 	"net/http/internal"
 	"net/http/internal/ascii"
@@ -954,9 +955,7 @@ func mergeSetHeader(dst *Header, src Header) {
 		*dst = src
 		return
 	}
-	for k, vv := range src {
-		(*dst)[k] = vv
-	}
+	maps.Copy(*dst, src)
 }
 
 // unreadDataSizeLocked returns the number of bytes of unread input.