Introduce a separate serve protocol

To start, it is just a clone of the common protocol. But now that we
have the separate protocol implementations, we can add versioning
information without the versions of one protocol leaking into another.

Using the infrastructure from the previous commit, we don't have to
duplicate code for shared behavior.

Motivation: No more perverse incentives. [0] did some awkward things
because the serializers did not store the version. I don't want anyone
making changes to be pushed towards keeping the serialization logic with
the core data types just because it's easier or the alternative is
tedious.

[0]: fe1f34f

Author: Ericson2314

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_
+
 }