From 499ffaf940a172990385f67f54d62c08d7ee3a0f Mon Sep 17 00:00:00 2001
From: Sergei Zimmerman <sergei@zimmerman.foo>
Date: Fri, 6 Feb 2026 20:55:04 +0300
Subject: [PATCH] NarIndexer: Implement skip

This improves the performance of parseNarListing, which is used by commands
like `nix nar ls` when the underlying source allows cheap seeks (like StringSource
or FdSource that does lseek).

For `nix nar ls` of a NAR for linux source tarball this cuts down the runtime almost
in half (from 300ms -> 175ms).
---
 src/libutil/nar-listing.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/libutil/nar-listing.cc b/src/libutil/nar-listing.cc
index 1483c7a0c..2a9011d70 100644
--- a/src/libutil/nar-listing.cc
+++ b/src/libutil/nar-listing.cc
@@ -112,6 +112,12 @@ NarListing parseNarListing(Source & source)
             pos += n;
             return n;
         }
+
+        void skip(size_t len) override
+        {
+            source.skip(len);
+            pos += len;
+        }
     };
 
     NarIndexer indexer(source);