diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 1f40dc42a..dc636c33f 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1864,11 +1864,11 @@ HookReply DerivationGoal::tryBuildHook()
 
     /* Tell the hook all the inputs that have to be copied to the
        remote system. */
-    writeStorePaths(worker.store, hook->sink, inputPaths);
+    write(worker.store, hook->sink, inputPaths);
 
     /* Tell the hooks the missing outputs that have to be copied back
        from the remote system. */
-    writeStorePaths(worker.store, hook->sink, missingPaths);
+    write(worker.store, hook->sink, missingPaths);
 
     hook->sink = FdSink();
     hook->toHook.writeSide = -1;
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 9f7be6e1a..f92d384e5 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -256,11 +256,11 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopQueryValidPaths: {
-        auto paths = readStorePaths<StorePathSet>(*store, from);
+        auto paths = read(*store, from, Proxy<StorePathSet> {});
         logger->startWork();
         auto res = store->queryValidPaths(paths);
         logger->stopWork();
-        writeStorePaths(*store, to, res);
+        write(*store, to, res);
         break;
     }
 
@@ -276,11 +276,11 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopQuerySubstitutablePaths: {
-        auto paths = readStorePaths<StorePathSet>(*store, from);
+        auto paths = read(*store, from, Proxy<StorePathSet> {});
         logger->startWork();
         auto res = store->querySubstitutablePaths(paths);
         logger->stopWork();
-        writeStorePaths(*store, to, res);
+        write(*store, to, res);
         break;
     }
 
@@ -309,7 +309,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
             paths = store->queryValidDerivers(path);
         else paths = store->queryDerivationOutputs(path);
         logger->stopWork();
-        writeStorePaths(*store, to, paths);
+        write(*store, to, paths);
         break;
     }
 
@@ -397,7 +397,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopAddTextToStore: {
         string suffix = readString(from);
         string s = readString(from);
-        auto refs = readStorePaths<StorePathSet>(*store, from);
+        auto refs = read(*store, from, Proxy<StorePathSet> {});
         logger->startWork();
         auto path = store->addTextToStore(suffix, s, refs, NoRepair);
         logger->stopWork();
@@ -518,7 +518,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopCollectGarbage: {
         GCOptions options;
         options.action = (GCOptions::GCAction) readInt(from);
-        options.pathsToDelete = readStorePaths<StorePathSet>(*store, from);
+        options.pathsToDelete = read(*store, from, Proxy<StorePathSet> {});
         from >> options.ignoreLiveness >> options.maxFreed;
         // obsolete fields
         readInt(from);
@@ -587,7 +587,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         else {
             to << 1
                << (i->second.deriver ? store->printStorePath(*i->second.deriver) : "");
-            writeStorePaths(*store, to, i->second.references);
+            write(*store, to, i->second.references);
             to << i->second.downloadSize
                << i->second.narSize;
         }
@@ -598,11 +598,11 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         SubstitutablePathInfos infos;
         StorePathCAMap pathsMap = {};
         if (GET_PROTOCOL_MINOR(clientVersion) < 22) {
-            auto paths = readStorePaths<StorePathSet>(*store, from);
+            auto paths = read(*store, from, Proxy<StorePathSet> {});
             for (auto & path : paths)
                 pathsMap.emplace(path, std::nullopt);
         } else
-            pathsMap = readStorePathCAMap(*store, from);
+            pathsMap = read(*store, from, Proxy<StorePathCAMap> {});
         logger->startWork();
         store->querySubstitutablePathInfos(pathsMap, infos);
         logger->stopWork();
@@ -610,7 +610,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         for (auto & i : infos) {
             to << store->printStorePath(i.first)
                << (i.second.deriver ? store->printStorePath(*i.second.deriver) : "");
-            writeStorePaths(*store, to, i.second.references);
+            write(*store, to, i.second.references);
             to << i.second.downloadSize << i.second.narSize;
         }
         break;
@@ -620,7 +620,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         auto paths = store->queryAllValidPaths();
         logger->stopWork();
-        writeStorePaths(*store, to, paths);
+        write(*store, to, paths);
         break;
     }
 
@@ -639,7 +639,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                 to << 1;
             to << (info->deriver ? store->printStorePath(*info->deriver) : "")
                << info->narHash->to_string(Base16, false);
-            writeStorePaths(*store, to, info->references);
+            write(*store, to, info->references);
             to << info->registrationTime << info->narSize;
             if (GET_PROTOCOL_MINOR(clientVersion) >= 16) {
                 to << info->ultimate
@@ -699,7 +699,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (deriver != "")
             info.deriver = store->parseStorePath(deriver);
         info.narHash = Hash(readString(from), htSHA256);
-        info.references = readStorePaths<StorePathSet>(*store, from);
+        info.references = read(*store, from, Proxy<StorePathSet> {});
         from >> info.registrationTime >> info.narSize >> info.ultimate;
         info.sigs = readStrings<StringSet>(from);
         info.ca = parseContentAddressOpt(readString(from));
@@ -799,9 +799,9 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         uint64_t downloadSize, narSize;
         store->queryMissing(targets, willBuild, willSubstitute, unknown, downloadSize, narSize);
         logger->stopWork();
-        writeStorePaths(*store, to, willBuild);
-        writeStorePaths(*store, to, willSubstitute);
-        writeStorePaths(*store, to, unknown);
+        write(*store, to, willBuild);
+        write(*store, to, willSubstitute);
+        write(*store, to, unknown);
         to << downloadSize << narSize;
         break;
     }
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 7d0a5abeb..5972b5ad2 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -477,7 +477,7 @@ Source & readDerivation(Source & in, const Store & store, BasicDerivation & drv,
         drv.outputs.emplace(std::move(name), std::move(output));
     }
 
-    drv.inputSrcs = readStorePaths<StorePathSet>(store, in);
+    drv.inputSrcs = read(store, in, Proxy<StorePathSet> {});
     in >> drv.platform >> drv.builder;
     drv.args = readStrings<Strings>(in);
 
@@ -505,7 +505,7 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
             out << "" << "";
         }
     }
-    writeStorePaths(store, out, drv.inputSrcs);
+    write(store, out, drv.inputSrcs);
     out << drv.platform << drv.builder << drv.args;
     out << drv.env.size();
     for (auto & i : drv.env)
diff --git a/src/libstore/export-import.cc b/src/libstore/export-import.cc
index a0fc22264..c20c56156 100644
--- a/src/libstore/export-import.cc
+++ b/src/libstore/export-import.cc
@@ -45,7 +45,7 @@ void Store::exportPath(const StorePath & path, Sink & sink)
     teeSink
         << exportMagic
         << printStorePath(path);
-    writeStorePaths(*this, teeSink, info->references);
+    write(*this, teeSink, info->references);
     teeSink
         << (info->deriver ? printStorePath(*info->deriver) : "")
         << 0;
@@ -73,7 +73,7 @@ StorePaths Store::importPaths(Source & source, CheckSigsFlag checkSigs)
 
         //Activity act(*logger, lvlInfo, format("importing path '%s'") % info.path);
 
-        info.references = readStorePaths<StorePathSet>(*this, source);
+        info.references = read(*this, source, Proxy<StorePathSet> {});
 
         auto deriver = readString(source);
         if (deriver != "")
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 5d7566121..412e1950b 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -107,7 +107,7 @@ struct LegacySSHStore : public Store
             auto deriver = readString(conn->from);
             if (deriver != "")
                 info->deriver = parseStorePath(deriver);
-            info->references = readStorePaths<StorePathSet>(*this, conn->from);
+            info->references = read(*this, conn->from, Proxy<StorePathSet> {});
             readLongLong(conn->from); // download size
             info->narSize = readLongLong(conn->from);
 
@@ -139,7 +139,7 @@ struct LegacySSHStore : public Store
                 << printStorePath(info.path)
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << info.narHash->to_string(Base16, false);
-            writeStorePaths(*this, conn->to, info.references);
+            write(*this, conn->to, info.references);
             conn->to
                 << info.registrationTime
                 << info.narSize
@@ -168,7 +168,7 @@ struct LegacySSHStore : public Store
             conn->to
                 << exportMagic
                 << printStorePath(info.path);
-            writeStorePaths(*this, conn->to, info.references);
+            write(*this, conn->to, info.references);
             conn->to
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << 0
@@ -251,10 +251,10 @@ struct LegacySSHStore : public Store
         conn->to
             << cmdQueryClosure
             << includeOutputs;
-        writeStorePaths(*this, conn->to, paths);
+        write(*this, conn->to, paths);
         conn->to.flush();
 
-        for (auto & i : readStorePaths<StorePathSet>(*this, conn->from))
+        for (auto & i : read(*this, conn->from, Proxy<StorePathSet> {}))
             out.insert(i);
     }
 
@@ -267,10 +267,10 @@ struct LegacySSHStore : public Store
             << cmdQueryValidPaths
             << false // lock
             << maybeSubstitute;
-        writeStorePaths(*this, conn->to, paths);
+        write(*this, conn->to, paths);
         conn->to.flush();
 
-        return readStorePaths<StorePathSet>(*this, conn->from);
+        return read(*this, conn->from, Proxy<StorePathSet> {});
     }
 
     void connect() override
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 1200ab200..de50b3e2e 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -23,66 +23,44 @@
 namespace nix {
 
 
-template<> StorePathSet readStorePaths(const Store & store, Source & from)
-{
-    StorePathSet paths;
-    for (auto & i : readStrings<Strings>(from))
-        paths.insert(store.parseStorePath(i));
-    return paths;
-}
-
-
-void writeStorePaths(const Store & store, Sink & out, const StorePathSet & paths)
+void write(const Store & store, Sink & out, const StorePathSet & paths)
 {
     out << paths.size();
     for (auto & i : paths)
         out << store.printStorePath(i);
 }
 
+
+std::string read(const Store & store, Source & from, Proxy<std::string> _)
+{
+    return readString(from);
+}
+
+void write(const Store & store, Sink & out, const std::string & str)
+{
+    out << str;
+}
+
+
 StorePath read(const Store & store, Source & from, Proxy<StorePath> _)
 {
-	auto path = readString(from);
-	return store.parseStorePath(path);
+    return store.parseStorePath(readString(from));
 }
 
-StorePathCAMap readStorePathCAMap(const Store & store, Source & from)
-{
-    StorePathCAMap paths;
-    auto count = readNum<size_t>(from);
-    while (count--)
-        paths.insert_or_assign(store.parseStorePath(readString(from)), parseContentAddressOpt(readString(from)));
-    return paths;
-}
-
-void writeStorePathCAMap(const Store & store, Sink & out, const StorePathCAMap & paths)
-{
-    out << paths.size();
-    for (auto & i : paths) {
-        out << store.printStorePath(i.first);
-        out << renderContentAddress(i.second);
-    }
-}
-
-std::map<string, StorePath> readOutputPathMap(const Store & store, Source & from)
-{
-    std::map<string, StorePath> pathMap;
-    auto rawInput = readStrings<Strings>(from);
-    if (rawInput.size() % 2)
-        throw Error("got an odd number of elements from the daemon when trying to read a output path map");
-    auto curInput = rawInput.begin();
-    while (curInput != rawInput.end()) {
-        auto thisKey = *curInput++;
-        auto thisValue = *curInput++;
-        pathMap.emplace(thisKey, store.parseStorePath(thisValue));
-    }
-    return pathMap;
-}
-
-
 void write(const Store & store, Sink & out, const StorePath & storePath)
 {
-	auto path = store.printStorePath(storePath);
-	out << path;
+    out << store.printStorePath(storePath);
+}
+
+
+ContentAddress read(const Store & store, Source & from, Proxy<ContentAddress> _)
+{
+    return parseContentAddress(readString(from));
+}
+
+void write(const Store & store, Sink & out, const ContentAddress & ca)
+{
+    out << renderContentAddress(ca);
 }
 
 
@@ -319,9 +297,9 @@ StorePathSet RemoteStore::queryValidPaths(const StorePathSet & paths, Substitute
         return res;
     } else {
         conn->to << wopQueryValidPaths;
-        writeStorePaths(*this, conn->to, paths);
+        write(*this, conn->to, paths);
         conn.processStderr();
-        return readStorePaths<StorePathSet>(*this, conn->from);
+        return read(*this, conn->from, Proxy<StorePathSet> {});
     }
 }
 
@@ -331,7 +309,7 @@ StorePathSet RemoteStore::queryAllValidPaths()
     auto conn(getConnection());
     conn->to << wopQueryAllValidPaths;
     conn.processStderr();
-    return readStorePaths<StorePathSet>(*this, conn->from);
+    return read(*this, conn->from, Proxy<StorePathSet> {});
 }
 
 
@@ -348,9 +326,9 @@ StorePathSet RemoteStore::querySubstitutablePaths(const StorePathSet & paths)
         return res;
     } else {
         conn->to << wopQuerySubstitutablePaths;
-        writeStorePaths(*this, conn->to, paths);
+        write(*this, conn->to, paths);
         conn.processStderr();
-        return readStorePaths<StorePathSet>(*this, conn->from);
+        return read(*this, conn->from, Proxy<StorePathSet> {});
     }
 }
 
@@ -372,7 +350,7 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
             auto deriver = readString(conn->from);
             if (deriver != "")
                 info.deriver = parseStorePath(deriver);
-            info.references = readStorePaths<StorePathSet>(*this, conn->from);
+            info.references = read(*this, conn->from, Proxy<StorePathSet> {});
             info.downloadSize = readLongLong(conn->from);
             info.narSize = readLongLong(conn->from);
             infos.insert_or_assign(i.first, std::move(info));
@@ -385,9 +363,9 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
             StorePathSet paths;
             for (auto & path : pathsMap)
                 paths.insert(path.first);
-            writeStorePaths(*this, conn->to, paths);
+            write(*this, conn->to, paths);
         } else
-            writeStorePathCAMap(*this, conn->to, pathsMap);
+            write(*this, conn->to, pathsMap);
         conn.processStderr();
         size_t count = readNum<size_t>(conn->from);
         for (size_t n = 0; n < count; n++) {
@@ -395,7 +373,7 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
             auto deriver = readString(conn->from);
             if (deriver != "")
                 info.deriver = parseStorePath(deriver);
-            info.references = readStorePaths<StorePathSet>(*this, conn->from);
+            info.references = read(*this, conn->from, Proxy<StorePathSet> {});
             info.downloadSize = readLongLong(conn->from);
             info.narSize = readLongLong(conn->from);
         }
@@ -428,7 +406,7 @@ void RemoteStore::queryPathInfoUncached(const StorePath & path,
             auto deriver = readString(conn->from);
             if (deriver != "") info->deriver = parseStorePath(deriver);
             info->narHash = Hash(readString(conn->from), htSHA256);
-            info->references = readStorePaths<StorePathSet>(*this, conn->from);
+            info->references = read(*this, conn->from, Proxy<StorePathSet> {});
             conn->from >> info->registrationTime >> info->narSize;
             if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
                 conn->from >> info->ultimate;
@@ -447,7 +425,7 @@ void RemoteStore::queryReferrers(const StorePath & path,
     auto conn(getConnection());
     conn->to << wopQueryReferrers << printStorePath(path);
     conn.processStderr();
-    for (auto & i : readStorePaths<StorePathSet>(*this, conn->from))
+    for (auto & i : read(*this, conn->from, Proxy<StorePathSet> {}))
         referrers.insert(i);
 }
 
@@ -457,7 +435,7 @@ StorePathSet RemoteStore::queryValidDerivers(const StorePath & path)
     auto conn(getConnection());
     conn->to << wopQueryValidDerivers << printStorePath(path);
     conn.processStderr();
-    return readStorePaths<StorePathSet>(*this, conn->from);
+    return read(*this, conn->from, Proxy<StorePathSet> {});
 }
 
 
@@ -469,7 +447,7 @@ StorePathSet RemoteStore::queryDerivationOutputs(const StorePath & path)
     }
     conn->to << wopQueryDerivationOutputs << printStorePath(path);
     conn.processStderr();
-    return readStorePaths<StorePathSet>(*this, conn->from);
+    return read(*this, conn->from, Proxy<StorePathSet> {});
 }
 
 
@@ -508,7 +486,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
             sink
                 << exportMagic
                 << printStorePath(info.path);
-            writeStorePaths(*this, sink, info.references);
+            write(*this, sink, info.references);
             sink
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << 0 // == no legacy signature
@@ -518,7 +496,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
 
         conn.processStderr(0, source2.get());
 
-        auto importedPaths = readStorePaths<StorePathSet>(*this, conn->from);
+        auto importedPaths = read(*this, conn->from, Proxy<StorePathSet> {});
         assert(importedPaths.size() <= 1);
     }
 
@@ -527,7 +505,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
                  << printStorePath(info.path)
                  << (info.deriver ? printStorePath(*info.deriver) : "")
                  << info.narHash->to_string(Base16, false);
-        writeStorePaths(*this, conn->to, info.references);
+        write(*this, conn->to, info.references);
         conn->to << info.registrationTime << info.narSize
                  << info.ultimate << info.sigs << renderContentAddress(info.ca)
                  << repair << !checkSigs;
@@ -660,7 +638,7 @@ StorePath RemoteStore::addTextToStore(const string & name, const string & s,
 
     auto conn(getConnection());
     conn->to << wopAddTextToStore << name << s;
-    writeStorePaths(*this, conn->to, references);
+    write(*this, conn->to, references);
 
     conn.processStderr();
     return parseStorePath(readString(conn->from));
@@ -762,7 +740,7 @@ void RemoteStore::collectGarbage(const GCOptions & options, GCResults & results)
 
     conn->to
         << wopCollectGarbage << options.action;
-    writeStorePaths(*this, conn->to, options.pathsToDelete);
+    write(*this, conn->to, options.pathsToDelete);
     conn->to << options.ignoreLiveness
         << options.maxFreed
         /* removed options */
@@ -824,9 +802,9 @@ void RemoteStore::queryMissing(const std::vector<StorePathWithOutputs> & targets
             ss.push_back(p.to_string(*this));
         conn->to << ss;
         conn.processStderr();
-        willBuild = readStorePaths<StorePathSet>(*this, conn->from);
-        willSubstitute = readStorePaths<StorePathSet>(*this, conn->from);
-        unknown = readStorePaths<StorePathSet>(*this, conn->from);
+        willBuild = read(*this, conn->from, Proxy<StorePathSet> {});
+        willSubstitute = read(*this, conn->from, Proxy<StorePathSet> {});
+        unknown = read(*this, conn->from, Proxy<StorePathSet> {});
         conn->from >> downloadSize >> narSize;
         return;
     }
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 4c68709ef..e894d2b85 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -362,14 +362,14 @@ bool Store::PathInfoCacheValue::isKnownNow()
 }
 
 OutputPathMap Store::queryDerivationOutputMapAssumeTotal(const StorePath & path) {
-	auto resp = queryDerivationOutputMap(path);
-	OutputPathMap result;
-	for (auto & [outName, optOutPath] : resp) {
-		if (!optOutPath)
-			throw Error("output '%s' has no store path mapped to it", outName);
-		result.insert_or_assign(outName, *optOutPath);
-	}
-	return result;
+    auto resp = queryDerivationOutputMap(path);
+    OutputPathMap result;
+    for (auto & [outName, optOutPath] : resp) {
+        if (!optOutPath)
+            throw Error("output '%s' has no store path mapped to it", outName);
+        result.insert_or_assign(outName, *optOutPath);
+    }
+    return result;
 }
 
 StorePathSet Store::queryDerivationOutputs(const StorePath & path)
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index ad5854c85..08eec9b48 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -66,33 +66,50 @@ typedef enum {
 class Store;
 struct Source;
 
-template<class T> T readStorePaths(const Store & store, Source & from);
-
-void writeStorePaths(const Store & store, Sink & out, const StorePathSet & paths);
-
 /* To guide overloading */
 template<typename T>
 struct Proxy {};
 
 template<typename T>
-std::map<std::string, T> read(const Store & store, Source & from, Proxy<std::map<std::string, T>> _)
+std::set<T> read(const Store & store, Source & from, Proxy<std::set<T>> _)
 {
-    std::map<string, T> resMap;
-    auto size = (size_t)readInt(from);
+    std::set<T> resSet;
+    auto size = readNum<size_t>(from);
     while (size--) {
-        auto thisKey = readString(from);
-        resMap.insert_or_assign(std::move(thisKey), read(store, from, Proxy<T> {}));
+        resSet.insert(read(store, from, Proxy<T> {}));
+    }
+    return resSet;
+}
+
+template<typename T>
+void write(const Store & store, Sink & out, const std::set<T> & resSet)
+{
+    out << resSet.size();
+    for (auto & key : resSet) {
+        write(store, out, key);
+    }
+}
+
+template<typename K, typename V>
+std::map<K, V> read(const Store & store, Source & from, Proxy<std::map<K, V>> _)
+{
+    std::map<K, V> resMap;
+    auto size = readNum<size_t>(from);
+    while (size--) {
+        resMap.insert_or_assign(
+            read(store, from, Proxy<K> {}),
+            read(store, from, Proxy<V> {}));
     }
     return resMap;
 }
 
-template<typename T>
-void write(const Store & store, Sink & out, const std::map<string, T> & resMap)
+template<typename K, typename V>
+void write(const Store & store, Sink & out, const std::map<K, V> & resMap)
 {
     out << resMap.size();
-    for (auto & i : resMap) {
-        out << i.first;
-        write(store, out, i.second);
+    for (auto & [key, value] : resMap) {
+        write(store, out, key);
+        write(store, out, value);
     }
 }
 
@@ -106,26 +123,28 @@ std::optional<T> read(const Store & store, Source & from, Proxy<std::optional<T>
     case 1:
         return read(store, from, Proxy<T> {});
     default:
-        throw Error("got an invalid tag bit for std::optional: %#04x", tag);
+        throw Error("got an invalid tag bit for std::optional: %#04x", (size_t)tag);
     }
 }
 
 template<typename T>
 void write(const Store & store, Sink & out, const std::optional<T> & optVal)
 {
-    out << (optVal ? 1 : 0);
+    out << (uint64_t) (optVal ? 1 : 0);
     if (optVal)
         write(store, out, *optVal);
 }
 
+std::string read(const Store & store, Source & from, Proxy<std::string> _);
+
+void write(const Store & store, Sink & out, const std::string & str);
+
 StorePath read(const Store & store, Source & from, Proxy<StorePath> _);
 
 void write(const Store & store, Sink & out, const StorePath & storePath);
 
-StorePathCAMap readStorePathCAMap(const Store & store, Source & from);
+ContentAddress read(const Store & store, Source & from, Proxy<ContentAddress> _);
 
-void writeStorePathCAMap(const Store & store, Sink & out, const StorePathCAMap & paths);
-
-void writeOutputPathMap(const Store & store, Sink & out, const OutputPathMap & paths);
+void write(const Store & store, Sink & out, const ContentAddress & ca);
 
 }
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 7b26970ef..a1fb921ef 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -815,7 +815,7 @@ static void opServe(Strings opFlags, Strings opArgs)
             case cmdQueryValidPaths: {
                 bool lock = readInt(in);
                 bool substitute = readInt(in);
-                auto paths = readStorePaths<StorePathSet>(*store, in);
+                auto paths = read(*store, in, Proxy<StorePathSet> {});
                 if (lock && writeAllowed)
                     for (auto & path : paths)
                         store->addTempRoot(path);
@@ -845,19 +845,19 @@ static void opServe(Strings opFlags, Strings opArgs)
                         }
                 }
 
-                writeStorePaths(*store, out, store->queryValidPaths(paths));
+                write(*store, out, store->queryValidPaths(paths));
                 break;
             }
 
             case cmdQueryPathInfos: {
-                auto paths = readStorePaths<StorePathSet>(*store, in);
+                auto paths = read(*store, in, Proxy<StorePathSet> {});
                 // !!! Maybe we want a queryPathInfos?
                 for (auto & i : paths) {
                     try {
                         auto info = store->queryPathInfo(i);
                         out << store->printStorePath(info->path)
                             << (info->deriver ? store->printStorePath(*info->deriver) : "");
-                        writeStorePaths(*store, out, info->references);
+                        write(*store, out, info->references);
                         // !!! Maybe we want compression?
                         out << info->narSize // downloadSize
                             << info->narSize;
@@ -885,7 +885,7 @@ static void opServe(Strings opFlags, Strings opArgs)
 
             case cmdExportPaths: {
                 readInt(in); // obsolete
-                store->exportPaths(readStorePaths<StorePathSet>(*store, in), out);
+                store->exportPaths(read(*store, in, Proxy<StorePathSet> {}), out);
                 break;
             }
 
@@ -934,9 +934,9 @@ static void opServe(Strings opFlags, Strings opArgs)
             case cmdQueryClosure: {
                 bool includeOutputs = readInt(in);
                 StorePathSet closure;
-                store->computeFSClosure(readStorePaths<StorePathSet>(*store, in),
+                store->computeFSClosure(read(*store, in, Proxy<StorePathSet> {}),
                     closure, false, includeOutputs);
-                writeStorePaths(*store, out, closure);
+                write(*store, out, closure);
                 break;
             }
 
@@ -949,7 +949,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                 if (deriver != "")
                     info.deriver = store->parseStorePath(deriver);
                 info.narHash = Hash(readString(in), htSHA256);
-                info.references = readStorePaths<StorePathSet>(*store, in);
+                info.references = read(*store, in, Proxy<StorePathSet> {});
                 in >> info.registrationTime >> info.narSize >> info.ultimate;
                 info.sigs = readStrings<StringSet>(in);
                 info.ca = parseContentAddressOpt(readString(in));