add support for fs.FS, embed.FS (in addition of string and http.FileSystem) for i18n locales and view engine's templates

context/context_fs.go

@@ -5,17 +5,102 @@ import (
 	"fmt"
 	"io/fs"
 	"net/http"
+	"os"
 	"path"
+	"path/filepath"
 )
 
 // ResolveFS accepts a single input argument of any type
-// and tries to cast it to http.FileSystem.
+// and tries to cast it to fs.FS.
 //
-// It affects the view engine filesystem resolver
-// and the Application's API Builder's `HandleDir` method.
+// It affects the view engine's filesystem resolver.
 //
 // This package-level variable can be modified on initialization.
-var ResolveFS = func(fsOrDir interface{}) http.FileSystem {
+var ResolveFS = func(fsOrDir interface{}) fs.FS {
+	if fsOrDir == nil {
+		return noOpFS{}
+	}
+
+	switch v := fsOrDir.(type) {
+	case string:
+		if v == "" {
+			return noOpFS{}
+		}
+		return os.DirFS(v)
+	case fs.FS:
+		return v
+	case http.FileSystem: // handles go-bindata.
+		return &httpFS{v}
+	default:
+		panic(fmt.Errorf(`unexpected "fsOrDir" argument type of %T (string or fs.FS or embed.FS or http.FileSystem)`, v))
+	}
+}
+
+type noOpFS struct{}
+
+func (fileSystem noOpFS) Open(name string) (fs.File, error) { return nil, nil }
+
+// IsNoOpFS reports whether the given "fileSystem" is a no operation fs.
+func IsNoOpFS(fileSystem fs.FS) bool {
+	_, ok := fileSystem.(noOpFS)
+	return ok
+}
+
+type httpFS struct {
+	fs http.FileSystem
+}
+
+func (f *httpFS) Open(name string) (fs.File, error) {
+	if name == "." {
+		name = "/"
+	}
+
+	return f.fs.Open(filepath.ToSlash(name))
+}
+
+func (f *httpFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	name = filepath.ToSlash(name)
+	if name == "." {
+		name = "/"
+	}
+
+	file, err := f.fs.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	infos, err := file.Readdir(-1)
+	if err != nil {
+		return nil, err
+	}
+
+	entries := make([]fs.DirEntry, 0, len(infos))
+	for _, info := range infos {
+		if info.IsDir() { // http file's does not return the whole tree, so read it.
+			sub, err := f.ReadDir(info.Name())
+			if err != nil {
+				return nil, err
+			}
+
+			entries = append(entries, sub...)
+			continue
+		}
+
+		entry := fs.FileInfoToDirEntry(info)
+		entries = append(entries, entry)
+	}
+
+	return entries, nil
+}
+
+// ResolveHTTPFS accepts a single input argument of any type
+// and tries to cast it to http.FileSystem.
+//
+// It affects the Application's API Builder's `HandleDir` method.
+//
+// This package-level variable can be modified on initialization.
+var ResolveHTTPFS = func(fsOrDir interface{}) http.FileSystem {
 	var fileSystem http.FileSystem
 	switch v := fsOrDir.(type) {
 	case string: