Move /src to /subprojects

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

subprojects/libstore/common-protocol.cc

@@ -0,0 +1,97 @@
+#include "serialise.hh"
+#include "path-with-outputs.hh"
+#include "store-api.hh"
+#include "build-result.hh"
+#include "common-protocol.hh"
+#include "common-protocol-impl.hh"
+#include "archive.hh"
+#include "derivations.hh"
+
+#include <nlohmann/json.hpp>
+
+namespace nix {
+
+/* protocol-agnostic definitions */
+
+std::string CommonProto::Serialise<std::string>::read(const StoreDirConfig & store, CommonProto::ReadConn conn)
+{
+    return readString(conn.from);
+}
+
+void CommonProto::Serialise<std::string>::write(const StoreDirConfig & store, CommonProto::WriteConn conn, const std::string & str)
+{
+    conn.to << str;
+}
+
+
+StorePath CommonProto::Serialise<StorePath>::read(const StoreDirConfig & store, CommonProto::ReadConn conn)
+{
+    return store.parseStorePath(readString(conn.from));
+}
+
+void CommonProto::Serialise<StorePath>::write(const StoreDirConfig & store, CommonProto::WriteConn conn, const StorePath & storePath)
+{
+    conn.to << store.printStorePath(storePath);
+}
+
+
+ContentAddress CommonProto::Serialise<ContentAddress>::read(const StoreDirConfig & store, CommonProto::ReadConn conn)
+{
+    return ContentAddress::parse(readString(conn.from));
+}
+
+void CommonProto::Serialise<ContentAddress>::write(const StoreDirConfig & store, CommonProto::WriteConn conn, const ContentAddress & ca)
+{
+    conn.to << renderContentAddress(ca);
+}
+
+
+Realisation CommonProto::Serialise<Realisation>::read(const StoreDirConfig & store, CommonProto::ReadConn conn)
+{
+    std::string rawInput = readString(conn.from);
+    return Realisation::fromJSON(
+        nlohmann::json::parse(rawInput),
+        "remote-protocol"
+    );
+}
+
+void CommonProto::Serialise<Realisation>::write(const StoreDirConfig & store, CommonProto::WriteConn conn, const Realisation & realisation)
+{
+    conn.to << realisation.toJSON().dump();
+}
+
+
+DrvOutput CommonProto::Serialise<DrvOutput>::read(const StoreDirConfig & store, CommonProto::ReadConn conn)
+{
+    return DrvOutput::parse(readString(conn.from));
+}
+
+void CommonProto::Serialise<DrvOutput>::write(const StoreDirConfig & store, CommonProto::WriteConn conn, const DrvOutput & drvOutput)
+{
+    conn.to << drvOutput.to_string();
+}
+
+
+std::optional<StorePath> CommonProto::Serialise<std::optional<StorePath>>::read(const StoreDirConfig & store, CommonProto::ReadConn conn)
+{
+    auto s = readString(conn.from);
+    return s == "" ? std::optional<StorePath> {} : store.parseStorePath(s);
+}
+
+void CommonProto::Serialise<std::optional<StorePath>>::write(const StoreDirConfig & store, CommonProto::WriteConn conn, const std::optional<StorePath> & storePathOpt)
+{
+    conn.to << (storePathOpt ? store.printStorePath(*storePathOpt) : "");
+}
+
+
+std::optional<ContentAddress> CommonProto::Serialise<std::optional<ContentAddress>>::read(const StoreDirConfig & store, CommonProto::ReadConn conn)
+{
+    return ContentAddress::parseOpt(readString(conn.from));
+}
+
+void CommonProto::Serialise<std::optional<ContentAddress>>::write(const StoreDirConfig & store, CommonProto::WriteConn conn, const std::optional<ContentAddress> & caOpt)
+{
+    conn.to << (caOpt ? renderContentAddress(*caOpt) : "");
+}
+
+}