Move /src to /subprojects

This will facilitate breaking up Nix into multiple packages for each
component with Meson.

subprojects/libstore/serve-protocol-connection.hh

@@ -0,0 +1,108 @@
+#pragma once
+///@file
+
+#include "serve-protocol.hh"
+#include "store-api.hh"
+
+namespace nix {
+
+struct ServeProto::BasicClientConnection
+{
+    FdSink to;
+    FdSource from;
+    ServeProto::Version remoteVersion;
+
+    /**
+     * Establishes connection, negotiating version.
+     *
+     * @return the version provided by the other side of the
+     * connection.
+     *
+     * @param to Taken by reference to allow for various error handling
+     * mechanisms.
+     *
+     * @param from Taken by reference to allow for various error
+     * handling mechanisms.
+     *
+     * @param localVersion Our version which is sent over
+     *
+     * @param host Just used to add context to thrown exceptions.
+     */
+    static ServeProto::Version
+    handshake(BufferedSink & to, Source & from, ServeProto::Version localVersion, std::string_view host);
+
+    /**
+     * Coercion to `ServeProto::ReadConn`. This makes it easy to use the
+     * factored out serve protocol serializers with a
+     * `LegacySSHStore::Connection`.
+     *
+     * The serve protocol connection types are unidirectional, unlike
+     * this type.
+     */
+    operator ServeProto::ReadConn()
+    {
+        return ServeProto::ReadConn{
+            .from = from,
+            .version = remoteVersion,
+        };
+    }
+
+    /**
+     * Coercion to `ServeProto::WriteConn`. This makes it easy to use the
+     * factored out serve protocol serializers with a
+     * `LegacySSHStore::Connection`.
+     *
+     * The serve protocol connection types are unidirectional, unlike
+     * this type.
+     */
+    operator ServeProto::WriteConn()
+    {
+        return ServeProto::WriteConn{
+            .to = to,
+            .version = remoteVersion,
+        };
+    }
+
+    StorePathSet queryValidPaths(
+        const StoreDirConfig & remoteStore, bool lock, const StorePathSet & paths, SubstituteFlag maybeSubstitute);
+
+    std::map<StorePath, UnkeyedValidPathInfo> queryPathInfos(const StoreDirConfig & store, const StorePathSet & paths);
+    ;
+
+    void putBuildDerivationRequest(
+        const StoreDirConfig & store,
+        const StorePath & drvPath,
+        const BasicDerivation & drv,
+        const ServeProto::BuildOptions & options);
+
+    /**
+     * Get the response, must be paired with
+     * `putBuildDerivationRequest`.
+     */
+    BuildResult getBuildDerivationResponse(const StoreDirConfig & store);
+
+    void narFromPath(const StoreDirConfig & store, const StorePath & path, std::function<void(Source &)> fun);
+
+    void importPaths(const StoreDirConfig & store, std::function<void(Sink &)> fun);
+};
+
+struct ServeProto::BasicServerConnection
+{
+    /**
+     * Establishes connection, negotiating version.
+     *
+     * @return the version provided by the other side of the
+     * connection.
+     *
+     * @param to Taken by reference to allow for various error handling
+     * mechanisms.
+     *
+     * @param from Taken by reference to allow for various error
+     * handling mechanisms.
+     *
+     * @param localVersion Our version which is sent over
+     */
+    static ServeProto::Version handshake(BufferedSink & to, Source & from, ServeProto::Version localVersion);
+};
+
+}