bug: fixed --base-path option to be respected with using embedded file system to serve static files (#367)

* bug: fixed `--base-path` option to be respected with using embedded file system to serve static files

* fix issues pointed out by gemini-code-assist

Author: kyasbal

pkg/server/embedfs.go

@@ -0,0 +1,53 @@
+// Copyright 2025 Google LLC
+//
+// 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 server
+
+import (
+	"embed"
+	"io/fs"
+	"log/slog"
+	"net/http"
+	"strings"
+
+	"github.com/gin-contrib/static"
+)
+
+// embedFileSystem is a gin middleware to serve static files from embedded file system.
+// The original implementation in gin-contrib/static somehow didn't consider the prefix thus this implementation just ported them here with replacing the prefix handling.
+type embedFileSystem struct {
+	http.FileSystem
+}
+
+func (e embedFileSystem) Exists(prefix string, path string) bool {
+	if !strings.HasPrefix(path, prefix) {
+		return false
+	}
+	_, err := e.Open(strings.TrimPrefix(path, prefix))
+	return err == nil
+}
+
+func embedFolder(fsEmbed embed.FS, targetPath string) static.ServeFileSystem {
+	fsys, err := fs.Sub(fsEmbed, targetPath)
+	if err != nil {
+		slog.Error("Failed to embed folder",
+			"targetPath", targetPath,
+			"error", err,
+		)
+		return nil
+	}
+	return embedFileSystem{
+		FileSystem: http.FS(fsys),
+	}
+}

pkg/server/embedfs_test.go

@@ -0,0 +1,62 @@
+// Copyright 2025 Google LLC
+//
+// 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 server
+
+import (
+	"embed"
+	"testing"
+)
+
+//go:embed dist
+var embeddedStaticFolderTest embed.FS
+
+func TestEmbedFolder_Exists(t *testing.T) {
+	testCases := []struct {
+		desc   string
+		prefix string
+		path   string
+		want   bool
+	}{
+		{
+			desc:   "file exists at root",
+			prefix: "/",
+			path:   "/index.html",
+			want:   true,
+		},
+		{
+			desc:   "file exists at root with prefix",
+			prefix: "/proxy/foo",
+			path:   "/proxy/foo/index.html",
+			want:   true,
+		},
+		{
+			desc:   "file doesn't exists at root with prefix",
+			prefix: "/proxy/foo",
+			path:   "index.html",
+			want:   false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			fs := embedFolder(embeddedStaticFolderTest, "dist")
+
+			got := fs.Exists(tc.prefix, tc.path)
+			if got != tc.want {
+				t.Errorf("Exists(%q, %q) = %v, want %v", tc.prefix, tc.path, got, tc.want)
+			}
+		})
+	}
+}

pkg/server/server.go

@@ -68,7 +68,7 @@ func CreateKHIServer(engine *gin.Engine, inspectionServer *coreinspection.Inspec
 
 	// By default, use the embedded web files. If the static folder path is set, use the local file system.
 	appHtmlPath := path.Join(embeddedStaticFolderPath, "/index.html")
-	webFS := static.EmbedFolder(embeddedStaticFolder, embeddedStaticFolderPath)
+	webFS := embedFolder(embeddedStaticFolder, embeddedStaticFolderPath)
 	webFSDebugMessage := "Using embedded static web files."
 	fileReaderFunc := embeddedStaticFolder.ReadFile
 	if serverConfig.StaticFolderPath != "" {