Introduce separate Serve protocol serialisers

src/libstore/legacy-ssh-store.cc

@@ -3,11 +3,10 @@
 #include "pool.hh"
 #include "remote-store.hh"
 #include "serve-protocol.hh"
+#include "serve-protocol-impl.hh"
 #include "build-result.hh"
 #include "store-api.hh"
 #include "path-with-outputs.hh"
-#include "common-protocol.hh"
-#include "common-protocol-impl.hh"
 #include "ssh.hh"
 #include "derivations.hh"
 #include "callback.hh"
@@ -50,37 +49,31 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
         bool good = true;
 
         /**
-         * Coercion to `CommonProto::ReadConn`. This makes it easy to use the
-         * factored out common protocol serialisers with a
+         * Coercion to `ServeProto::ReadConn`. This makes it easy to use the
+         * factored out serve protocol searlizers with a
          * `LegacySSHStore::Connection`.
          *
-         * The common protocol connection types are unidirectional, unlike
+         * The serve protocol connection types are unidirectional, unlike
          * this type.
-         *
-         * @todo Use server protocol serializers, not common protocol
-         * serializers, once we have made that distiction.
          */
-        operator CommonProto::ReadConn ()
+        operator ServeProto::ReadConn ()
         {
-            return CommonProto::ReadConn {
+            return ServeProto::ReadConn {
                 .from = from,
             };
         }
 
         /*
-         * Coercion to `CommonProto::WriteConn`. This makes it easy to use the
-         * factored out common protocol searlizers with a
+         * Coercion to `ServeProto::WriteConn`. This makes it easy to use the
+         * factored out serve protocol searlizers with a
          * `LegacySSHStore::Connection`.
          *
-         * The common protocol connection types are unidirectional, unlike
+         * The serve protocol connection types are unidirectional, unlike
          * this type.
-         *
-         * @todo Use server protocol serializers, not common protocol
-         * serializers, once we have made that distiction.
          */
-        operator CommonProto::WriteConn ()
+        operator ServeProto::WriteConn ()
         {
-            return CommonProto::WriteConn {
+            return ServeProto::WriteConn {
                 .to = to,
             };
         }
@@ -183,7 +176,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
             auto deriver = readString(conn->from);
             if (deriver != "")
                 info->deriver = parseStorePath(deriver);
-            info->references = CommonProto::Serialise<StorePathSet>::read(*this, *conn);
+            info->references = ServeProto::Serialise<StorePathSet>::read(*this, *conn);
             readLongLong(conn->from); // download size
             info->narSize = readLongLong(conn->from);
 
@@ -217,7 +210,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
                 << printStorePath(info.path)
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << info.narHash.to_string(Base16, false);
-            CommonProto::write(*this, *conn, info.references);
+            ServeProto::write(*this, *conn, info.references);
             conn->to
                 << info.registrationTime
                 << info.narSize
@@ -246,7 +239,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
             conn->to
                 << exportMagic
                 << printStorePath(info.path);
-            CommonProto::write(*this, *conn, info.references);
+            ServeProto::write(*this, *conn, info.references);
             conn->to
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << 0
@@ -331,7 +324,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
         if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 3)
             conn->from >> status.timesBuilt >> status.isNonDeterministic >> status.startTime >> status.stopTime;
         if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 6) {
-            auto builtOutputs = CommonProto::Serialise<DrvOutputs>::read(*this, *conn);
+            auto builtOutputs = ServeProto::Serialise<DrvOutputs>::read(*this, *conn);
             for (auto && [output, realisation] : builtOutputs)
                 status.builtOutputs.insert_or_assign(
                     std::move(output.outputName),
@@ -409,10 +402,10 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
         conn->to
             << ServeProto::Command::QueryClosure
             << includeOutputs;
-        CommonProto::write(*this, *conn, paths);
+        ServeProto::write(*this, *conn, paths);
         conn->to.flush();
 
-        for (auto & i : CommonProto::Serialise<StorePathSet>::read(*this, *conn))
+        for (auto & i : ServeProto::Serialise<StorePathSet>::read(*this, *conn))
             out.insert(i);
     }
 
@@ -425,10 +418,10 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
             << ServeProto::Command::QueryValidPaths
             << false // lock
             << maybeSubstitute;
-        CommonProto::write(*this, *conn, paths);
+        ServeProto::write(*this, *conn, paths);
         conn->to.flush();
 
-        return CommonProto::Serialise<StorePathSet>::read(*this, *conn);
+        return ServeProto::Serialise<StorePathSet>::read(*this, *conn);
     }
 
     void connect() override

src/libstore/serve-protocol-impl.hh

@@ -0,0 +1,59 @@
+#pragma once
+/**
+ * @file
+ *
+ * Template implementations (as opposed to mere declarations).
+ *
+ * This file is an exmample of the "impl.hh" pattern. See the
+ * contributing guide.
+ */
+
+#include "serve-protocol.hh"
+#include "length-prefixed-protocol-helper.hh"
+
+namespace nix {
+
+/* protocol-agnostic templates */
+
+#define SERVE_USE_LENGTH_PREFIX_SERIALISER(TEMPLATE, T) \
+    TEMPLATE T ServeProto::Serialise< T >::read(const Store & store, ServeProto::ReadConn conn) \
+    { \
+        return LengthPrefixedProtoHelper<ServeProto, T >::read(store, conn); \
+    } \
+    TEMPLATE void ServeProto::Serialise< T >::write(const Store & store, ServeProto::WriteConn conn, const T & t) \
+    { \
+        LengthPrefixedProtoHelper<ServeProto, T >::write(store, conn, t); \
+    }
+
+SERVE_USE_LENGTH_PREFIX_SERIALISER(template<typename T>, std::vector<T>)
+SERVE_USE_LENGTH_PREFIX_SERIALISER(template<typename T>, std::set<T>)
+SERVE_USE_LENGTH_PREFIX_SERIALISER(template<typename... Ts>, std::tuple<Ts...>)
+
+#define COMMA_ ,
+SERVE_USE_LENGTH_PREFIX_SERIALISER(
+    template<typename K COMMA_ typename V>,
+    std::map<K COMMA_ V>)
+#undef COMMA_
+
+/**
+ * Use `CommonProto` where possible.
+ */
+template<typename T>
+struct ServeProto::Serialise
+{
+    static T read(const Store & store, ServeProto::ReadConn conn)
+    {
+        return CommonProto::Serialise<T>::read(store,
+            CommonProto::ReadConn { .from = conn.from });
+    }
+    static void write(const Store & store, ServeProto::WriteConn conn, const T & t)
+    {
+        CommonProto::Serialise<T>::write(store,
+            CommonProto::WriteConn { .to = conn.to },
+            t);
+    }
+};
+
+/* protocol-specific templates */
+
+}

src/libstore/serve-protocol.cc

@@ -0,0 +1,15 @@
+#include "serialise.hh"
+#include "util.hh"
+#include "path-with-outputs.hh"
+#include "store-api.hh"
+#include "serve-protocol.hh"
+#include "serve-protocol-impl.hh"
+#include "archive.hh"
+
+#include <nlohmann/json.hpp>
+
+namespace nix {
+
+/* protocol-specific definitions */
+
+}

src/libstore/serve-protocol.hh

@@ -1,6 +1,8 @@
 #pragma once
 ///@file
 
+#include "common-protocol.hh"
+
 namespace nix {
 
 #define SERVE_MAGIC_1 0x390c9deb
@@ -10,6 +12,11 @@ namespace nix {
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
+
+class Store;
+struct Source;
+
+
 /**
  * The "serve protocol", used by ssh:// stores.
  *
@@ -22,6 +29,57 @@ struct ServeProto
      * Enumeration of all the request types for the protocol.
      */
     enum struct Command : uint64_t;
+
+    /**
+     * A unidirectional read connection, to be used by the read half of the
+     * canonical serializers below.
+     *
+     * This currently is just a `Source &`, but more fields will be added
+     * later.
+     */
+    struct ReadConn {
+        Source & from;
+    };
+
+    /**
+     * A unidirectional write connection, to be used by the write half of the
+     * canonical serializers below.
+     *
+     * This currently is just a `Sink &`, but more fields will be added
+     * later.
+     */
+    struct WriteConn {
+        Sink & to;
+    };
+
+    /**
+     * Data type for canonical pairs of serialisers for the serve protocol.
+     *
+     * See https://en.cppreference.com/w/cpp/language/adl for the broader
+     * concept of what is going on here.
+     */
+    template<typename T>
+    struct Serialise;
+    // This is the definition of `Serialise` we *want* to put here, but
+    // do not do so.
+    //
+    // See `worker-protocol.hh` for a longer explanation.
+#if 0
+    {
+        static T read(const Store & store, ReadConn conn);
+        static void write(const Store & store, WriteConn conn, const T & t);
+    };
+#endif
+
+    /**
+     * Wrapper function around `ServeProto::Serialise<T>::write` that allows us to
+     * infer the type instead of having to write it down explicitly.
+     */
+    template<typename T>
+    static void write(const Store & store, WriteConn conn, const T & t)
+    {
+        ServeProto::Serialise<T>::write(store, conn, t);
+    }
 };
 
 enum struct ServeProto::Command : uint64_t
@@ -58,4 +116,33 @@ inline std::ostream & operator << (std::ostream & s, ServeProto::Command op)
     return s << (uint64_t) op;
 }
 
+/**
+ * Declare a canonical serialiser pair for the worker protocol.
+ *
+ * We specialise the struct merely to indicate that we are implementing
+ * the function for the given type.
+ *
+ * Some sort of `template<...>` must be used with the caller for this to
+ * be legal specialization syntax. See below for what that looks like in
+ * practice.
+ */
+#define DECLARE_SERVE_SERIALISER(T) \
+    struct ServeProto::Serialise< T > \
+    { \
+        static T read(const Store & store, ServeProto::ReadConn conn); \
+        static void write(const Store & store, ServeProto::WriteConn conn, const T & t); \
+    };
+
+template<typename T>
+DECLARE_SERVE_SERIALISER(std::vector<T>);
+template<typename T>
+DECLARE_SERVE_SERIALISER(std::set<T>);
+template<typename... Ts>
+DECLARE_SERVE_SERIALISER(std::tuple<Ts...>);
+
+#define COMMA_ ,
+template<typename K, typename V>
+DECLARE_SERVE_SERIALISER(std::map<K COMMA_ V>);
+#undef COMMA_
+
 }