Add FSPrefix to ignore parent dir of assets

README.md

@@ -95,15 +95,13 @@ Files with extensions ".gz", ".br", ".gif", ".jpg", ".png", ".webp" are excluded
 
 ### Mounting a subdirectory
 
-It may be convenient to strip leading directory from an embedded file system, you can do that with `fs.Sub` and a type
-assertion.
+It may be convenient to strip leading directory from an embedded file system, you can do that with `statigz.FSPrefix`.
 
 ```go
 package main
 
 import (
 	"embed"
-	"io/fs"
 	"log"
 	"net/http"
 
@@ -117,14 +115,8 @@ import (
 var st embed.FS
 
 func main() {
-	// Retrieve sub directory.
-	sub, err := fs.Sub(st, "static")
-	if err != nil {
-		log.Fatal(err)
-	}
-
 	// Plug static assets handler to your server or router.
-	err = http.ListenAndServe(":80", statigz.FileServer(sub.(fs.ReadDirFS), brotli.AddEncoding))
+	err := http.ListenAndServe(":80", statigz.FileServer(st, brotli.AddEncoding, statigz.FSPrefix("static")))
 	if err != nil {
 		log.Fatal(err)
 	}

server.go

@@ -48,8 +48,16 @@ type Server struct {
 	// of large embeddings, use with caution.
 	EncodeOnInit bool
 
-	info map[string]fileInfo
-	fs   fs.ReadDirFS
+	// FSPrefix is a path prefix shat should be ignored.
+	// It is prepended to the incoming HTTP path.
+	// This can help to keep static assets in a subdirectory, e.g.
+	//   //go:embed static/*
+	// But access files from HTTP without "/static/" prefix in the path.
+	FSPrefix string
+
+	info     map[string]fileInfo
+	fs       fs.ReadDirFS
+	fsPrefix string
 }
 
 const (
@@ -89,6 +97,10 @@ func FileServer(fs fs.ReadDirFS, options ...func(server *Server)) *Server {
 		o(&s)
 	}
 
+	if s.FSPrefix != "" {
+		s.fsPrefix = strings.Trim(s.FSPrefix, "/") + "/"
+	}
+
 	// Reading from "." is not expected to fail.
 	if err := s.hashDir("."); err != nil {
 		panic(err)
@@ -319,7 +331,7 @@ func (s *Server) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		return
 	}
 
-	fn := strings.TrimPrefix(req.URL.Path, "/")
+	fn := s.fsPrefix + strings.TrimPrefix(req.URL.Path, "/")
 	ae := req.Header.Get("Accept-Encoding")
 
 	if s.info[fn].isDir {
@@ -375,7 +387,7 @@ func (s *Server) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 //
 // This can be useful for custom handling of requests to non-existent resources.
 func (s *Server) Found(req *http.Request) bool {
-	fn := strings.TrimPrefix(req.URL.Path, "/")
+	fn := s.fsPrefix + strings.TrimPrefix(req.URL.Path, "/")
 	ae := req.Header.Get("Accept-Encoding")
 
 	if s.info[fn].isDir {
@@ -486,6 +498,13 @@ func EncodeOnInit(server *Server) {
 	server.EncodeOnInit = true
 }
 
+// FSPrefix declares file system path prefix that should be ignored.
+func FSPrefix(prefix string) func(server *Server) {
+	return func(server *Server) {
+		server.FSPrefix = prefix
+	}
+}
+
 // localRedirect gives a Moved Permanently response.
 // It does not convert relative paths to absolute paths like Redirect does.
 //

server_test.go

@@ -86,6 +86,8 @@ func TestServer_ServeHTTP_found(t *testing.T) {
 		} else {
 			assert.Equal(t, http.StatusNotFound, rw.Code, u)
 		}
+
+		assert.Equal(t, found, s.Found(req))
 	}
 
 	for u, l := range map[string]string{
@@ -375,3 +377,31 @@ func ExampleServer_Found() {
 		log.Fatal(err)
 	}
 }
+
+func TestServer_ServeHTTP_FSPrefix(t *testing.T) {
+	s := statigz.FileServer(v, brotli.AddEncoding, statigz.EncodeOnInit, statigz.FSPrefix("testdata"))
+
+	for u, found := range map[string]bool{
+		"/favicon.png":         true,
+		"/nonexistent":         false,
+		"/swagger.json":        true,
+		"/deeper/swagger.json": true,
+		"/deeper/openapi.json": true,
+		"/":                    true,
+	} {
+		req, err := http.NewRequest(http.MethodGet, u, nil)
+		require.NoError(t, err)
+
+		rw := httptest.NewRecorder()
+		s.ServeHTTP(rw, req)
+
+		if found {
+			assert.Equal(t, "", rw.Header().Get("Content-Encoding"))
+			assert.Equal(t, http.StatusOK, rw.Code, u)
+		} else {
+			assert.Equal(t, http.StatusNotFound, rw.Code, u)
+		}
+
+		assert.Equal(t, found, s.Found(req))
+	}
+}