feat: serve files using embed.FS (#4847)

rest/internal/fileserver/filehandler.go

@@ -2,6 +2,7 @@ package fileserver
 
 import (
 	"net/http"
+	pathpkg "path"
 	"strings"
 	"sync"
 )
@@ -29,6 +30,18 @@ func createFileChecker(fs http.FileSystem) func(string) bool {
 	fileChecker := make(map[string]bool)
 
 	return func(path string) bool {
+		// Emulate http.Dir.Open’s path normalization for embed.FS.Open.
+		// http.FileServer redirects any request ending in "/index.html"
+		// to the same path without the final "index.html".
+		// So the path here may be empty or end with a "/".
+		// http.Dir.Open uses this logic to clean the path,
+		// correctly handling those two cases.
+		// embed.FS doesn’t perform this normalization, so we apply the same logic here.
+		path = pathpkg.Clean("/" + path)[1:]
+		if path == "" {
+			path = "."
+		}
+
 		lock.RLock()
 		exist, ok := fileChecker[path]
 		lock.RUnlock()