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BinaryCacheStore::narFromPath(): Fix unreachable code #14643

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Merged
edolstra merged 2 commits into from
Nov 26, 2025
Merged

BinaryCacheStore::narFromPath(): Fix unreachable code #14643

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d7b6afe
LambdaSink: Allow passing a destructor callback
edolstra Nov 25, 2025
7ba8443
BinaryCacheStore::narFromPath(): Fix unreachable code
edolstra Nov 25, 2025
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20 changes: 14 additions & 6 deletions src/libstore/binary-cache-store.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -418,10 +418,20 @@ void BinaryCacheStore::narFromPath(const StorePath & storePath, Sink & sink)
{
auto info = queryPathInfo(storePath).cast<const NarInfo>();

LengthSink narSize;
TeeSink tee{sink, narSize};
uint64_t narSize = 0;

auto decompressor = makeDecompressionSink(info->compression, tee);
LambdaSink uncompressedSink{
[&](std::string_view data) {
narSize += data.size();
sink(data);
},
[&]() {
stats.narRead++;
// stats.narReadCompressedBytes += nar->size(); // FIXME
stats.narReadBytes += narSize;
}};

auto decompressor = makeDecompressionSink(info->compression, uncompressedSink);

try {
getFile(info->url, *decompressor);
Expand All @@ -431,9 +441,7 @@ void BinaryCacheStore::narFromPath(const StorePath & storePath, Sink & sink)

decompressor->finish();

stats.narRead++;
// stats.narReadCompressedBytes += nar->size(); // FIXME
stats.narReadBytes += narSize.length;
// Note: don't do anything here because it's never reached if we're called as a coroutine.
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@xokdvium xokdvium Nov 25, 2025 •
edited
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But if this code doesn't run then how is the destructor (for LambdaSink) being run? Would be nice to add a unit test for the issue so it's more clear what's being fixed

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@edolstra edolstra Nov 26, 2025

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Boost unwinds the coroutine stack by throwing an exception of type boost::context::detail::forced_unwind. So destructors of stack variables do get executed.

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@xokdvium xokdvium Nov 27, 2025

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Thanks!

}

void BinaryCacheStore::queryPathInfoUncached(
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19 changes: 14 additions & 5 deletions src/libutil/include/nix/util/serialise.hh
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Expand Up @@ -447,18 +447,27 @@ struct LengthSource : Source
*/
struct LambdaSink : Sink
{
typedef std::function<void(std::string_view data)> lambda_t;
typedef std::function<void(std::string_view data)> data_t;
typedef std::function<void()> cleanup_t;

lambda_t lambda;
data_t dataFun;
cleanup_t cleanupFun;

LambdaSink(const lambda_t & lambda)
: lambda(lambda)
LambdaSink(
const data_t & dataFun, const cleanup_t & cleanupFun = []() {})
: dataFun(dataFun)
, cleanupFun(cleanupFun)
{
}

~LambdaSink()
{
cleanupFun();
}

void operator()(std::string_view data) override
{
lambda(data);
dataFun(data);
}
};

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