fix race?

Signed-off-by: Lixia (Sylvia) Lei <lixlei@microsoft.com>

internal/maps/maps.go

@@ -0,0 +1,28 @@
+/*
+Copyright The ORAS Authors.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package maps
+
+// Copy copies all key/value pairs in src adding them to dst.
+// When a key in src is already present in dst,
+// the value in dst will be overwritten by the value associated
+// with the key in src.
+//
+// Reference: https://pkg.go.dev/maps@go1.21.1#Copy
+func Copy[M1 ~map[K]V, M2 ~map[K]V, K comparable, V any](dst M1, src M2) {
+	for k, v := range src {
+		dst[k] = v
+	}
+}

registry/remote/auth/scope.go

@@ -20,6 +20,7 @@ import (
 	"sort"
 	"strings"
 
+	"oras.land/oras-go/v2/internal/maps"
 	"oras.land/oras-go/v2/internal/slices"
 	"oras.land/oras-go/v2/registry"
 )
@@ -146,15 +147,16 @@ type scopesPerHostContextKey struct{}
 //
 // Reference: https://docs.docker.com/registry/spec/auth/scope/
 func WithScopesPerHost(ctx context.Context, host string, scopes ...string) context.Context {
-	var regMap map[string][]string
-	var ok bool
-	regMap, ok = ctx.Value(scopesPerHostContextKey{}).(map[string][]string)
-	if !ok {
-		regMap = make(map[string][]string)
+	var scopesByHost map[string][]string
+	if old, ok := ctx.Value(scopesPerHostContextKey{}).(map[string][]string); ok {
+		scopesByHost = make(map[string][]string, len(old))
+		maps.Copy(scopesByHost, old)
+	} else {
+		scopesByHost = make(map[string][]string, 1)
 	}
-	scopes = CleanScopes(scopes)
-	regMap[host] = scopes
-	return context.WithValue(ctx, scopesPerHostContextKey{}, regMap)
+
+	scopesByHost[host] = CleanScopes(scopes)
+	return context.WithValue(ctx, scopesPerHostContextKey{}, scopesByHost)
 }
 
 // AppendScopesPerHost appends additional scopes to the existing scopes
@@ -171,8 +173,8 @@ func AppendScopesPerHost(ctx context.Context, host string, scopes ...string) con
 
 // GetScopesPerHost returns the scopes in the context for the given host.
 func GetScopesPerHost(ctx context.Context, host string) []string {
-	if regMap, ok := ctx.Value(scopesPerHostContextKey{}).(map[string][]string); ok {
-		return slices.Clone(regMap[host])
+	if scopesByHost, ok := ctx.Value(scopesPerHostContextKey{}).(map[string][]string); ok {
+		return slices.Clone(scopesByHost[host])
 	}
 	return nil
 }