diff --git a/lix/legacy/nix-store.cc b/lix/legacy/nix-store.cc
index d5c3d8fda..20dfc7412 100644
--- a/lix/legacy/nix-store.cc
+++ b/lix/legacy/nix-store.cc
@@ -763,7 +763,7 @@ static void opVerifyPath(Strings opFlags, Strings opArgs)
         printMsg(lvlTalkative, "checking path '%s'...", store->printStorePath(path));
         auto info = store->queryPathInfo(path);
         HashSink sink(info->narHash.type);
-        sink << store->narFromPath(path);
+        store->narFromPath(path)->drainInto(sink);
         auto current = sink.finish();
         if (current.first != info->narHash) {
             printError("path '%s' was modified! expected hash '%s', got '%s'",
@@ -900,7 +900,7 @@ static void opServe(Strings opFlags, Strings opArgs)
             }
 
             case ServeProto::Command::DumpStorePath:
-                out << store->narFromPath(store->parseStorePath(readString(in)));
+                store->narFromPath(store->parseStorePath(readString(in)))->drainInto(out);
                 break;
 
             case ServeProto::Command::ImportPaths: {
diff --git a/lix/libstore/binary-cache-store.cc b/lix/libstore/binary-cache-store.cc
index 609dc962a..a9301df3c 100644
--- a/lix/libstore/binary-cache-store.cc
+++ b/lix/libstore/binary-cache-store.cc
@@ -317,13 +317,13 @@ std::optional<StorePath> BinaryCacheStore::queryPathFromHashPart(const std::stri
     }
 }
 
-WireFormatGenerator BinaryCacheStore::narFromPath(const StorePath & storePath)
+box_ptr<Source> BinaryCacheStore::narFromPath(const StorePath & storePath)
 {
     auto info = queryPathInfo(storePath).cast<const NarInfo>();
 
     try {
         auto file = getFile(info->url);
-        return [](auto info, auto file, auto & stats) -> WireFormatGenerator {
+        return make_box_ptr<GeneratorSource>([](auto info, auto file, auto & stats) -> WireFormatGenerator {
             constexpr size_t buflen = 65536;
             auto buf = std::make_unique<char []>(buflen);
             size_t total = 0;
@@ -340,7 +340,7 @@ WireFormatGenerator BinaryCacheStore::narFromPath(const StorePath & storePath)
             stats.narRead++;
             //stats.narReadCompressedBytes += nar->size(); // FIXME
             stats.narReadBytes += total;
-        }(std::move(info), std::move(file), stats);
+        }(std::move(info), std::move(file), stats));
     } catch (NoSuchBinaryCacheFile & e) {
         throw SubstituteGone(std::move(e.info()));
     }
diff --git a/lix/libstore/binary-cache-store.hh b/lix/libstore/binary-cache-store.hh
index a8a393133..c251ca108 100644
--- a/lix/libstore/binary-cache-store.hh
+++ b/lix/libstore/binary-cache-store.hh
@@ -138,7 +138,7 @@ public:
 
     std::shared_ptr<const Realisation> queryRealisationUncached(const DrvOutput &) override;
 
-    WireFormatGenerator narFromPath(const StorePath & path) override;
+    box_ptr<Source> narFromPath(const StorePath & path) override;
 
     ref<FSAccessor> getFSAccessor() override;
 
diff --git a/lix/libstore/build/local-derivation-goal.cc b/lix/libstore/build/local-derivation-goal.cc
index 060d4acca..ddf628077 100644
--- a/lix/libstore/build/local-derivation-goal.cc
+++ b/lix/libstore/build/local-derivation-goal.cc
@@ -1076,7 +1076,7 @@ struct RestrictedStore : public virtual IndirectRootStore, public virtual GcStor
         return path;
     }
 
-    WireFormatGenerator narFromPath(const StorePath & path) override
+    box_ptr<Source> narFromPath(const StorePath & path) override
     {
         if (!goal.isAllowed(path))
             throw InvalidPath("cannot dump unknown path '%s' in recursive Nix", printStorePath(path));
diff --git a/lix/libstore/dummy-store.cc b/lix/libstore/dummy-store.cc
index caf333d80..38da8110e 100644
--- a/lix/libstore/dummy-store.cc
+++ b/lix/libstore/dummy-store.cc
@@ -65,7 +65,7 @@ struct DummyStore final : public Store
         RepairFlag repair) override
     { unsupported("addTextToStore"); }
 
-    WireFormatGenerator narFromPath(const StorePath & path) override
+    box_ptr<Source> narFromPath(const StorePath & path) override
     { unsupported("narFromPath"); }
 
     std::shared_ptr<const Realisation> queryRealisationUncached(const DrvOutput &) override
diff --git a/lix/libstore/export-import.cc b/lix/libstore/export-import.cc
index a79c1300a..a0caeff2e 100644
--- a/lix/libstore/export-import.cc
+++ b/lix/libstore/export-import.cc
@@ -28,7 +28,7 @@ void Store::exportPath(const StorePath & path, Sink & sink)
     HashSink hashSink(HashType::SHA256);
     TeeSink teeSink(sink, hashSink);
 
-    teeSink << narFromPath(path);
+    narFromPath(path)->drainInto(teeSink);
 
     /* Refuse to export paths that have changed.  This prevents
        filesystem corruption from spreading to other machines.
diff --git a/lix/libstore/legacy-ssh-store.cc b/lix/libstore/legacy-ssh-store.cc
index 3c36fefe6..f6a79dbbd 100644
--- a/lix/libstore/legacy-ssh-store.cc
+++ b/lix/libstore/legacy-ssh-store.cc
@@ -241,15 +241,15 @@ struct LegacySSHStore final : public Store
             throw Error("failed to add path '%s' to remote host '%s'", printStorePath(info.path), host);
     }
 
-    WireFormatGenerator narFromPath(const StorePath & path) override
+    box_ptr<Source> narFromPath(const StorePath & path) override
     {
         auto conn(connections->get());
 
         conn->to << ServeProto::Command::DumpStorePath << printStorePath(path);
         conn->to.flush();
-        return [] (auto conn) -> WireFormatGenerator {
+        return make_box_ptr<GeneratorSource>([] (auto conn) -> WireFormatGenerator {
             co_yield copyNAR(conn->from);
-        }(std::move(conn));
+        }(std::move(conn)));
     }
 
     std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override
diff --git a/lix/libstore/local-fs-store.cc b/lix/libstore/local-fs-store.cc
index 02481cef3..c385bbf3d 100644
--- a/lix/libstore/local-fs-store.cc
+++ b/lix/libstore/local-fs-store.cc
@@ -73,11 +73,11 @@ ref<FSAccessor> LocalFSStore::getFSAccessor()
             std::dynamic_pointer_cast<LocalFSStore>(shared_from_this())));
 }
 
-WireFormatGenerator LocalFSStore::narFromPath(const StorePath & path)
+box_ptr<Source> LocalFSStore::narFromPath(const StorePath & path)
 {
     if (!isValidPath(path))
         throw Error("path '%s' does not exist in store", printStorePath(path));
-    return dumpPath(getRealStoreDir() + std::string(printStorePath(path), config().storeDir.size()));
+    return make_box_ptr<GeneratorSource>(dumpPath(getRealStoreDir() + std::string(printStorePath(path), config().storeDir.size())));
 }
 
 const std::string LocalFSStore::drvsLogDir = "drvs";
diff --git a/lix/libstore/local-fs-store.hh b/lix/libstore/local-fs-store.hh
index 31eba2e66..b9ad4480b 100644
--- a/lix/libstore/local-fs-store.hh
+++ b/lix/libstore/local-fs-store.hh
@@ -42,7 +42,7 @@ public:
     LocalFSStoreConfig & config() override = 0;
     const LocalFSStoreConfig & config() const override = 0;
 
-    WireFormatGenerator narFromPath(const StorePath & path) override;
+    box_ptr<Source> narFromPath(const StorePath & path) override;
     ref<FSAccessor> getFSAccessor() override;
 
     /**
diff --git a/lix/libstore/make-content-addressed.cc b/lix/libstore/make-content-addressed.cc
index cdc3ad122..7c4535af5 100644
--- a/lix/libstore/make-content-addressed.cc
+++ b/lix/libstore/make-content-addressed.cc
@@ -24,7 +24,7 @@ std::map<StorePath, StorePath> makeContentAddressed(
         std::string oldHashPart(path.hashPart());
 
         StringSink sink;
-        sink << srcStore.narFromPath(path);
+        srcStore.narFromPath(path)->drainInto(sink);
 
         StringMap rewrites;
 
diff --git a/lix/libstore/remote-fs-accessor.cc b/lix/libstore/remote-fs-accessor.cc
index ce62653c4..af6d0a4a3 100644
--- a/lix/libstore/remote-fs-accessor.cc
+++ b/lix/libstore/remote-fs-accessor.cc
@@ -97,7 +97,7 @@ std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_, boo
     }
 
     StringSink sink;
-    sink << store->narFromPath(storePath);
+    store->narFromPath(storePath)->drainInto(sink);
     return {addToCache(storePath.hashPart(), std::move(sink.s)), restPath};
 }
 
diff --git a/lix/libstore/remote-store.cc b/lix/libstore/remote-store.cc
index 909e85ca7..46a3a2da7 100644
--- a/lix/libstore/remote-store.cc
+++ b/lix/libstore/remote-store.cc
@@ -861,14 +861,14 @@ RemoteStore::Connection::~Connection()
     }
 }
 
-WireFormatGenerator RemoteStore::narFromPath(const StorePath & path)
+box_ptr<Source> RemoteStore::narFromPath(const StorePath & path)
 {
     auto conn(connections->get());
     conn->to << WorkerProto::Op::NarFromPath << printStorePath(path);
     conn->processStderr();
-    return [](auto conn) -> WireFormatGenerator {
+    return make_box_ptr<GeneratorSource>([](auto conn) -> WireFormatGenerator {
         co_yield copyNAR(conn->from);
-    }(std::move(conn));
+    }(std::move(conn)));
 }
 
 ref<FSAccessor> RemoteStore::getFSAccessor()
diff --git a/lix/libstore/remote-store.hh b/lix/libstore/remote-store.hh
index df8d4f294..7e72ea089 100644
--- a/lix/libstore/remote-store.hh
+++ b/lix/libstore/remote-store.hh
@@ -185,7 +185,7 @@ protected:
 
     virtual ref<FSAccessor> getFSAccessor() override;
 
-    virtual WireFormatGenerator narFromPath(const StorePath & path) override;
+    virtual box_ptr<Source> narFromPath(const StorePath & path) override;
 
 private:
 
diff --git a/lix/libstore/store-api.cc b/lix/libstore/store-api.cc
index aca310fec..d4cba2105 100644
--- a/lix/libstore/store-api.cc
+++ b/lix/libstore/store-api.cc
@@ -1061,6 +1061,10 @@ static std::string makeCopyPathMessage(
 }
 
 
+// buffer size for path copy progress reporting. should be large enough to not cause excessive
+// overhead during copies, but small enough to provide reasonably quick copy progress updates.
+static constexpr unsigned PATH_COPY_BUFSIZE = 65536;
+
 void copyStorePath(
     Store & srcStore,
     Store & dstStore,
@@ -1103,11 +1107,17 @@ void copyStorePath(
     GeneratorSource source{
         [](auto & act, auto & info, auto & srcStore, auto & storePath) -> WireFormatGenerator {
             auto nar = srcStore.narFromPath(storePath);
+            auto buf = std::make_unique<char[]>(PATH_COPY_BUFSIZE);
             uint64_t total = 0;
-            while (auto data = nar.next()) {
-                total += data->size();
-                act.progress(total, info->narSize);
-                co_yield *data;
+            while (true) {
+                try {
+                    auto got = nar->read(buf.get(), PATH_COPY_BUFSIZE);
+                    total += got;
+                    act.progress(total, info->narSize);
+                    co_yield std::span{buf.get(), got};
+                } catch (EndOfFile &) {
+                    break;
+                }
             }
         }(act, info, srcStore, storePath)
     };
@@ -1239,11 +1249,17 @@ std::map<StorePath, StorePath> copyPaths(
             PushActivity pact(act.id);
 
             auto nar = srcStore.narFromPath(missingPath);
+            auto buf = std::make_unique<char[]>(PATH_COPY_BUFSIZE);
             uint64_t total = 0;
-            while (auto data = nar.next()) {
-                total += data->size();
-                act.progress(total, info->narSize);
-                co_yield *data;
+            while (true) {
+                try {
+                    auto got = nar->read(buf.get(), PATH_COPY_BUFSIZE);
+                    total += got;
+                    act.progress(total, info->narSize);
+                    co_yield std::span{buf.get(), got};
+                } catch (EndOfFile &) {
+                    break;
+                }
             }
         };
         pathsToCopy.push_back(std::pair{
diff --git a/lix/libstore/store-api.hh b/lix/libstore/store-api.hh
index 21ab07f70..7bd3300c8 100644
--- a/lix/libstore/store-api.hh
+++ b/lix/libstore/store-api.hh
@@ -580,7 +580,7 @@ public:
     /**
      * Generate a NAR dump of a store path.
      */
-    virtual WireFormatGenerator narFromPath(const StorePath & path) = 0;
+    virtual box_ptr<Source> narFromPath(const StorePath & path) = 0;
 
     /**
      * For each path, if it's a derivation, build it.  Building a
diff --git a/lix/libstore/uds-remote-store.hh b/lix/libstore/uds-remote-store.hh
index fbc8fa2e1..e39506c48 100644
--- a/lix/libstore/uds-remote-store.hh
+++ b/lix/libstore/uds-remote-store.hh
@@ -42,7 +42,7 @@ public:
     ref<FSAccessor> getFSAccessor() override
     { return LocalFSStore::getFSAccessor(); }
 
-    WireFormatGenerator narFromPath(const StorePath & path) override
+    box_ptr<Source> narFromPath(const StorePath & path) override
     { return LocalFSStore::narFromPath(path); }
 
     /**
diff --git a/lix/nix/dump-path.cc b/lix/nix/dump-path.cc
index be2bbcc7b..de3e8f302 100644
--- a/lix/nix/dump-path.cc
+++ b/lix/nix/dump-path.cc
@@ -22,7 +22,7 @@ struct CmdDumpPath : StorePathCommand
     {
         logger->pause();
         FdSink sink(STDOUT_FILENO);
-        sink << store->narFromPath(storePath);
+        store->narFromPath(storePath)->drainInto(sink);
         sink.flush();
     }
 };
diff --git a/lix/nix/verify.cc b/lix/nix/verify.cc
index f51f00888..64baae297 100644
--- a/lix/nix/verify.cc
+++ b/lix/nix/verify.cc
@@ -99,7 +99,7 @@ struct CmdVerify : StorePathsCommand
 
                     auto hashSink = HashSink(info->narHash.type);
 
-                    hashSink << store->narFromPath(info->path);
+                    store->narFromPath(info->path)->drainInto(hashSink);
 
                     auto hash = hashSink.finish();