1 files changed, 12 insertions, 0 deletions
diff --git a/src/libstore/nar-accessor.hh b/src/libstore/nar-accessor.hh
index ed8fe15cad23..2871199de16e 100644
--- a/src/libstore/nar-accessor.hh
+++ b/src/libstore/nar-accessor.hh
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <functional>
+
 #include "fs-accessor.hh"
 
 namespace nix {
@@ -8,6 +10,16 @@ namespace nix {
    file. */
 ref<FSAccessor> makeNarAccessor(ref<const std::string> nar);
 
+/* Create a NAR accessor from a NAR listing (in the format produced by
+   listNar()). The callback getNarBytes(offset, length) is used by the
+   readFile() method of the accessor to get the contents of files
+   inside the NAR. */
+typedef std::function<std::string(uint64_t, uint64_t)> GetNarBytes;
+
+ref<FSAccessor> makeLazyNarAccessor(
+    const std::string & listing,
+    GetNarBytes getNarBytes);
+
 class JSONPlaceholder;
 
 /* Write a JSON representation of the contents of a NAR (except file