diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index d33139092..f572b0a41 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -416,7 +416,7 @@ StorePath BinaryCacheStore::addToStore(
     if (method == FileIngestionMethod::Recursive) {
         sink << dumpPath(srcPath, filter);
     } else {
-        readFile(srcPath, sink);
+        sink << readFileSource(srcPath);
     }
     auto h = sink.finish().first;
 
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 37c8a7708..be82fd028 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -2454,7 +2454,7 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
             HashModuloSink caSink { outputHash.hashType, oldHashPart };
             std::visit(overloaded {
                 [&](const TextIngestionMethod &) {
-                    readFile(actualPath, caSink);
+                    caSink << readFileSource(actualPath);
                 },
                 [&](const FileIngestionMethod & m2) {
                     switch (m2) {
@@ -2462,7 +2462,7 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
                         caSink << dumpPath(actualPath);
                         break;
                     case FileIngestionMethod::Flat:
-                        readFile(actualPath, caSink);
+                        caSink << readFileSource(actualPath);
                         break;
                     }
                 },
diff --git a/src/libstore/local-binary-cache-store.cc b/src/libstore/local-binary-cache-store.cc
index 5684dcd80..5ba5bd802 100644
--- a/src/libstore/local-binary-cache-store.cc
+++ b/src/libstore/local-binary-cache-store.cc
@@ -71,7 +71,7 @@ protected:
     void getFile(const std::string & path, Sink & sink) override
     {
         try {
-            readFile(binaryCacheDir + "/" + path, sink);
+            sink << readFileSource(binaryCacheDir + "/" + path);
         } catch (SysError & e) {
             if (e.errNo == ENOENT)
                 throw NoSuchBinaryCacheFile("file '%s' does not exist in binary cache", path);
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 9c86a6b88..9d170d581 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -1886,7 +1886,7 @@ ContentAddress LocalStore::hashCAPath(
     HashModuloSink caSink ( hashType, std::string(pathHash) );
     std::visit(overloaded {
         [&](const TextIngestionMethod &) {
-            readFile(path, caSink);
+            caSink << readFileSource(path);
         },
         [&](const FileIngestionMethod & m2) {
             switch (m2) {
@@ -1894,7 +1894,7 @@ ContentAddress LocalStore::hashCAPath(
                 caSink << dumpPath(path);
                 break;
             case FileIngestionMethod::Flat:
-                readFile(path, caSink);
+                caSink << readFileSource(path);
                 break;
             }
         },
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index e1575deb3..bb32b1534 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -271,13 +271,12 @@ StorePath Store::addToStore(
     const StorePathSet & references)
 {
     Path srcPath(absPath(_srcPath));
-    auto source = sinkToSource([&](Sink & sink) {
-        if (method == FileIngestionMethod::Recursive)
-            sink << dumpPath(srcPath, filter);
-        else
-            readFile(srcPath, sink);
-    });
-    return addToStoreFromDump(*source, name, method, hashAlgo, repair, references);
+    auto source = WireSource{
+        method == FileIngestionMethod::Recursive
+        ? static_cast<Generator<std::span<const char>, void>>(dumpPath(srcPath, filter))
+        : readFileSource(srcPath)
+    };
+    return addToStoreFromDump(source, name, method, hashAlgo, repair, references);
 }
 
 void Store::addMultipleToStore(
diff --git a/src/libutil/generator.hh b/src/libutil/generator.hh
index ff524fe5d..d57de3fd3 100644
--- a/src/libutil/generator.hh
+++ b/src/libutil/generator.hh
@@ -10,29 +10,40 @@
 namespace nix {
 
 template<typename T, typename Transform = std::identity>
-struct Generator : private Generator<T, void>
+struct Generator
 {
     struct promise_type;
     using handle_type = std::coroutine_handle<promise_type>;
 
-    explicit Generator(handle_type h) : Generator<T, void>{h, h.promise().state} {}
+    explicit Generator(handle_type h) : impl{h, h.promise().state} {}
 
-    using Generator<T, void>::operator bool;
-    using Generator<T, void>::operator();
+    explicit operator bool()
+    {
+        return bool(impl);
+    }
+    T operator()()
+    {
+        return impl();
+    }
 
     operator Generator<T, void> &() &
     {
-        return *this;
+        return impl;
     }
     operator Generator<T, void>() &&
     {
-        return std::move(*this);
+        return std::move(impl);
     }
+
+private:
+    Generator<T, void> impl;
 };
 
 template<typename T>
 struct Generator<T, void>
 {
+    template<typename, typename>
+    friend struct Generator;
     template<typename T2, typename Transform>
     friend struct Generator<T2, Transform>::promise_type;
 
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 5dedbc221..5c268af20 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -325,7 +325,7 @@ Hash hashString(HashType ht, std::string_view s)
 Hash hashFile(HashType ht, const Path & path)
 {
     HashSink sink(ht);
-    readFile(path, sink);
+    sink << readFileSource(path);
     return sink.finish().first;
 }
 
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 3116ca742..f175bc258 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -388,7 +388,8 @@ void drainGenerator(Generator<std::span<const char>, T> g, std::derived_from<Sin
 
 struct WireSource : Source
 {
-    WireSource(WireFormatGenerator && g) : g(std::move(g)) {}
+    template<typename F>
+    explicit WireSource(Generator<std::span<const char>, F> g) : g(std::move(g)) {}
 
     virtual size_t read(char * data, size_t len)
     {
@@ -406,7 +407,7 @@ struct WireSource : Source
     }
 
 private:
-    WireFormatGenerator g;
+    Generator<std::span<const char>, void> g;
     std::span<const char> buf{};
 };
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index b46716511..822bfe9dc 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -366,12 +366,12 @@ std::string readFile(const Path & path)
 }
 
 
-void readFile(const Path & path, Sink & sink)
+Generator<std::span<const char>> readFileSource(const Path & path)
 {
     AutoCloseFD fd{open(path.c_str(), O_RDONLY | O_CLOEXEC)};
     if (!fd)
         throw SysError("opening file '%s'", path);
-    drainGenerator(drainFDSource(fd.get()), sink);
+    co_yield drainFDSource(fd.get());
 }
 
 
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index a7db52421..351561cdf 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -163,7 +163,7 @@ unsigned char getFileType(const Path & path);
  */
 std::string readFile(int fd);
 std::string readFile(const Path & path);
-void readFile(const Path & path, Sink & sink);
+Generator<std::span<const char>> readFileSource(const Path & path);
 
 /**
  * Write a string to a file.
diff --git a/src/nix/add-to-store.cc b/src/nix/add-to-store.cc
index c92e24fb8..7e16e12c3 100644
--- a/src/nix/add-to-store.cc
+++ b/src/nix/add-to-store.cc
@@ -37,7 +37,7 @@ struct CmdAddToStore : MixDryRun, StoreCommand
         Hash hash = narHash;
         if (ingestionMethod == FileIngestionMethod::Flat) {
             HashSink hsink(htSHA256);
-            readFile(path, hsink);
+            hsink << readFileSource(path);
             hash = hsink.finish().first;
         }
 
diff --git a/src/nix/hash.cc b/src/nix/hash.cc
index 6872dbd61..d9079d551 100644
--- a/src/nix/hash.cc
+++ b/src/nix/hash.cc
@@ -85,7 +85,7 @@ struct CmdHashBase : Command
 
             switch (mode) {
             case FileIngestionMethod::Flat:
-                readFile(path, *hashSink);
+                *hashSink << readFileSource(path);
                 break;
             case FileIngestionMethod::Recursive:
                 *hashSink << dumpPath(path);