Add http.NoListFS

Signed-off-by: Knut Ahlers <knut@ahlers.me>

http/nolistfs.go

@@ -0,0 +1,42 @@
+package http
+
+import (
+	"net/http"
+	"os"
+
+	"github.com/pkg/errors"
+)
+
+type (
+	// NoListFS wraps an http.FileSystem and ensures no directory
+	// listings are printed out in order not to expose the contents
+	// of the directory in a listing.
+	NoListFS struct{ Next http.FileSystem }
+)
+
+var _ http.FileSystem = NoListFS{}
+
+// Open wraps the Open of the inner http.FileSystem and returns an
+// os.ErrNotExist in case a directory should be opened. This will
+// result in a HTTP 404 when trying to open a directory causing the
+// contents to be conceiled in an effective manner (zero exposure
+// of known paths)
+func (n NoListFS) Open(name string) (http.File, error) {
+	f, err := n.Next.Open(name)
+	if err != nil {
+		return f, errors.Wrap(err, "opening file from inner fs")
+	}
+
+	info, err := f.Stat()
+	if err != nil {
+		f.Close()
+		return nil, errors.Wrap(err, "getting stat from opened file")
+	}
+
+	if info.IsDir() {
+		f.Close()
+		return nil, errors.Wrap(os.ErrNotExist, "refusing to open a directory")
+	}
+
+	return f, nil
+}