From 7d934f7880d460cba1ab908fd35b3d43e97a4749 Mon Sep 17 00:00:00 2001
From: pennae <github@quasiparticle.net>
Date: Fri, 19 Aug 2022 11:26:26 +0200
Subject: [PATCH] don't read outputs into memory for output rewriting

RewritingSink can handle being fed input where a reference crosses a
chunk boundary. we don't need to load the whole source into memory, and
in fact *not* loading the whole source lets nix build FODs that do not
fit into memory (eg fetchurl'ing data files larger than system memory).
---
 src/libstore/build/local-derivation-goal.cc | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 6843173a7..18b682e13 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -2374,10 +2374,8 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
             if (*scratchPath != finalPath) {
                 // Also rewrite the output path
                 auto source = sinkToSource([&](Sink & nextSink) {
-                    StringSink sink;
-                    dumpPath(actualPath, sink);
                     RewritingSink rsink2(oldHashPart, std::string(finalPath.hashPart()), nextSink);
-                    rsink2(sink.s);
+                    dumpPath(actualPath, rsink2);
                     rsink2.flush();
                 });
                 Path tmpPath = actualPath + ".tmp";