diff --git a/.envrc b/.envrc
index 3550a30f..4359d1f6 100644
--- a/.envrc
+++ b/.envrc
@@ -1 +1 @@
-use flake
+use flake .#clang
diff --git a/src/hydra-queue-runner/nar-extractor.cc b/src/hydra-queue-runner/nar-extractor.cc
index b3350193..31c0db65 100644
--- a/src/hydra-queue-runner/nar-extractor.cc
+++ b/src/hydra-queue-runner/nar-extractor.cc
@@ -7,8 +7,38 @@
 
 using namespace nix;
 
-struct Extractor : ParseSink
+struct Extractor : NARParseVisitor
 {
+    class MyFileHandle : public FileHandle
+    {
+        NarMemberData * memberData;
+        uint64_t expectedSize;
+        std::unique_ptr<HashSink> hashSink;
+
+        public:
+            MyFileHandle(NarMemberData * memberData, uint64_t size) : memberData(memberData)
+            {
+                expectedSize = size;
+                hashSink = std::make_unique<HashSink>(HashType::SHA256);
+            }
+
+            void receiveContents(std::string_view data) override
+            {
+                *memberData->fileSize += data.size();
+                (*hashSink)(data);
+                if (memberData->contents) {
+                    memberData->contents->append(data);
+                }
+                assert(memberData->fileSize <= expectedSize);
+                if (memberData->fileSize == expectedSize) {
+                    auto [hash, len] = hashSink->finish();
+                    assert(memberData->fileSize == len);
+                    memberData->sha256 = hash;
+                    hashSink.reset();
+                }
+            }
+    };
+
     std::unordered_set<Path> filesToKeep {
         "/nix-support/hydra-build-products",
         "/nix-support/hydra-release-name",
@@ -16,7 +46,6 @@ struct Extractor : ParseSink
     };
 
     NarMemberDatas & members;
-    NarMemberData * curMember = nullptr;
     Path prefix;
 
     Extractor(NarMemberDatas & members, Path  prefix)
@@ -28,41 +57,15 @@ struct Extractor : ParseSink
         members.insert_or_assign(prefix + path, NarMemberData { .type = FSAccessor::Type::tDirectory });
     }
 
-    void createRegularFile(const Path & path) override
+    std::unique_ptr<FileHandle> createRegularFile(const Path & path, uint64_t size, bool executable) override
     {
-        curMember = &members.insert_or_assign(prefix + path, NarMemberData {
+        auto memberData = &members.insert_or_assign(prefix + path, NarMemberData {
             .type = FSAccessor::Type::tRegular,
             .fileSize = 0,
             .contents = filesToKeep.count(path) ? std::optional("") : std::nullopt,
         }).first->second;
-    }
 
-    std::optional<uint64_t> expectedSize;
-    std::unique_ptr<HashSink> hashSink;
-
-    void preallocateContents(uint64_t size) override
-    {
-        expectedSize = size;
-        hashSink = std::make_unique<HashSink>(HashType::SHA256);
-    }
-
-    void receiveContents(std::string_view data) override
-    {
-        assert(expectedSize);
-        assert(curMember);
-        assert(hashSink);
-        *curMember->fileSize += data.size();
-        (*hashSink)(data);
-        if (curMember->contents) {
-            curMember->contents->append(data);
-        }
-        assert(curMember->fileSize <= expectedSize);
-        if (curMember->fileSize == expectedSize) {
-            auto [hash, len] = hashSink->finish();
-            assert(curMember->fileSize == len);
-            curMember->sha256 = hash;
-            hashSink.reset();
-        }
+        return std::unique_ptr<MyFileHandle>(new MyFileHandle{memberData, size});
     }
 
     void createSymlink(const Path & path, const std::string & target) override