feat: support file server in rest (#4244)

rest/internal/fileserver/filehandler.go

@@ -0,0 +1,39 @@
+package fileserver
+
+import (
+	"net/http"
+	"strings"
+)
+
+func Middleware(path, dir string) func(http.HandlerFunc) http.HandlerFunc {
+	fileServer := http.FileServer(http.Dir(dir))
+	pathWithTrailSlash := ensureTrailingSlash(path)
+	pathWithoutTrailSlash := ensureNoTrailingSlash(path)
+
+	return func(next http.HandlerFunc) http.HandlerFunc {
+		return func(w http.ResponseWriter, r *http.Request) {
+			if r.Method == http.MethodGet && strings.HasPrefix(r.URL.Path, pathWithTrailSlash) {
+				r.URL.Path = strings.TrimPrefix(r.URL.Path, pathWithoutTrailSlash)
+				fileServer.ServeHTTP(w, r)
+			} else {
+				next(w, r)
+			}
+		}
+	}
+}
+
+func ensureTrailingSlash(path string) string {
+	if strings.HasSuffix(path, "/") {
+		return path
+	}
+
+	return path + "/"
+}
+
+func ensureNoTrailingSlash(path string) string {
+	if strings.HasSuffix(path, "/") {
+		return path[:len(path)-1]
+	}
+
+	return path
+}