add a content-type filter to apiserver filters to autoset nosniff

staging/src/k8s.io/apiserver/pkg/server/filters/BUILD

@@ -10,6 +10,7 @@ go_test(
     name = "go_default_test",
     srcs = [
         "compression_test.go",
+        "content_type_test.go",
         "cors_test.go",
         "maxinflight_test.go",
         "timeout_test.go",
@@ -32,6 +33,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "compression.go",
+        "content_type.go",
         "cors.go",
         "doc.go",
         "longrunning.go",

staging/src/k8s.io/apiserver/pkg/server/filters/content_type.go

+/*
+Copyright 2019 The Kubernetes 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 filters
+
+import "net/http"
+
+// WithContentType sets both the Content-Type and the X-Content-Type-Options (nosniff) header
+func WithContentType(handler http.Handler, contentType string) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", contentType)
+		w.Header().Set("X-Content-Type-Options", "nosniff")
+		handler.ServeHTTP(w, r)
+	})
+}

staging/src/k8s.io/apiserver/pkg/server/filters/content_type_test.go

+/*
+Copyright 2019 The Kubernetes 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 filters
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func noopHandler() http.HandlerFunc {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// noop
+	})
+}
+
+func TestWithContentType(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.Handle("/text", WithContentType(noopHandler(), "text/plain"))
+	mux.Handle("/json", WithContentType(noopHandler(), "application/json"))
+	tests := []struct {
+		description      string
+		path             string
+		expectedMimeType string
+	}{
+		{"/text should return a plain text response", "/text", "text/plain"},
+		{"/json should return a json response", "/json", "application/json"},
+	}
+	for _, test := range tests {
+		path := "http://example.com" + test.path
+		t.Run(path, func(t *testing.T) {
+			req, err := http.NewRequest("GET", path, nil)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			w := httptest.NewRecorder()
+			mux.ServeHTTP(w, req)
+			if nosniffHeader := w.Header().Get("X-Content-Type-Options"); nosniffHeader != "nosniff" {
+				t.Errorf("expected nosniff header to be set, got %v", nosniffHeader)
+			}
+			if mimeTypeHeader := w.Header().Get("Content-Type"); mimeTypeHeader != test.expectedMimeType {
+				t.Errorf("expected %v, got %v", test.expectedMimeType, mimeTypeHeader)
+			}
+		})
+	}
+}