[WIP] libstore: remove a sinkToSouce from old daemon protocol

this doesn't have a test because this code path is only reached by
clients that predate 2.4, and we really should not be caring about
those any more right now. even the test suite doesn't, and the few
tests that might care are disabled because they will not even work

Change-Id: Id9eb190065138fedb2c7d90c328ff9eb9d97385b

src/libstore/daemon.cc

@@ -453,7 +453,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                 hashAlgo = parseHashType(hashAlgoRaw);
             }
 
-            auto dumpSource = sinkToSource([&](Sink & saved) {
+            GeneratorSource dumpSource{[&]() -> WireFormatGenerator {
                 if (method == FileIngestionMethod::Recursive) {
                     /* We parse the NAR dump through into `saved` unmodified,
                        so why all this extra work? We still parse the NAR so
@@ -463,18 +463,33 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                        command. (We don't trust `addToStoreFromDump` to not
                        eagerly consume the entire stream it's given, past the
                        length of the Nar. */
-                    saved << copyNAR(from);
+                    co_yield copyNAR(from);
                 } else {
                     /* Incrementally parse the NAR file, stripping the
                        metadata, and streaming the sole file we expect into
                        `saved`. */
-                    RetrieveRegularNARSink savedRegular { saved };
-                    parseDump(savedRegular, from);
-                    if (!savedRegular.regular) throw Error("regular file expected");
+                    auto parser = nar::parse(from);
+                    nar::File * file = nullptr;
+                    while (auto entry = parser.next()) {
+                        file = std::visit(
+                            overloaded{
+                                [](nar::MetadataString) -> nar::File * { return nullptr; },
+                                [](nar::MetadataRaw) -> nar::File * { return nullptr; },
+                                [](nar::File & f) -> nar::File * { return &f; },
+                                [](auto &) -> nar::File * { throw Error("regular file expected"); },
+                            },
+                            *entry
+                        );
+                        if (file) {
+                            break;
+                        }
+                    }
+                    assert(file); // should never fail unless the nar is empty, which would be invalid
+                    co_yield std::move(file->contents);
                 }
-            });
+            }()};
             logger->startWork();
-            auto path = store->addToStoreFromDump(*dumpSource, baseName, method, hashAlgo);
+            auto path = store->addToStoreFromDump(dumpSource, baseName, method, hashAlgo);
             logger->stopWork();
 
             to << store->printStorePath(path);