Factor out bits of the worker protocol to use elsewhere

doc/internal-api/doxygen.cfg.in

@@ -54,10 +54,40 @@ INPUT                  = \
   src/nix-env \
   src/nix-store
 
+# If the MACRO_EXPANSION tag is set to YES, doxygen will expand all macro names
+# in the source code. If set to NO, only conditional compilation will be
+# performed. Macro expansion can be done in a controlled way by setting
+# EXPAND_ONLY_PREDEF to YES.
+# The default value is: NO.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+MACRO_EXPANSION        = YES
+
+# If the EXPAND_ONLY_PREDEF and MACRO_EXPANSION tags are both set to YES then
+# the macro expansion is limited to the macros specified with the PREDEFINED and
+# EXPAND_AS_DEFINED tags.
+# The default value is: NO.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+EXPAND_ONLY_PREDEF     = YES
+
 # The INCLUDE_PATH tag can be used to specify one or more directories that
 # contain include files that are not input files but should be processed by the
 # preprocessor. Note that the INCLUDE_PATH is not recursive, so the setting of
 # RECURSIVE has no effect here.
 # This tag requires that the tag SEARCH_INCLUDES is set to YES.
 
 INCLUDE_PATH           = @RAPIDCHECK_HEADERS@
+
+# If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
+# tag can be used to specify a list of macro names that should be expanded. The
+# macro definition that is found in the sources will be used. Use the PREDEFINED
+# tag if you want to use a different macro definition that overrules the
+# definition found in the source code.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+EXPAND_AS_DEFINED      = \
+  DECLARE_COMMON_SERIALISER \
+  DECLARE_WORKER_SERIALISER \
+  DECLARE_SERVE_SERIALISER \
+  LENGTH_PREFIXED_PROTO_HELPER

src/libstore/build/derivation-goal.cc

@@ -8,8 +8,8 @@
 #include "util.hh"
 #include "archive.hh"
 #include "compression.hh"
-#include "worker-protocol.hh"
-#include "worker-protocol-impl.hh"
+#include "common-protocol.hh"
+#include "common-protocol-impl.hh"
 #include "topo-sort.hh"
 #include "callback.hh"
 #include "local-store.hh" // TODO remove, along with remaining downcasts
@@ -1185,11 +1185,11 @@ HookReply DerivationGoal::tryBuildHook()
         throw;
     }
 
-    WorkerProto::WriteConn conn { hook->sink };
+    CommonProto::WriteConn conn { hook->sink };
 
     /* Tell the hook all the inputs that have to be copied to the
        remote system. */
-    WorkerProto::write(worker.store, conn, inputPaths);
+    CommonProto::write(worker.store, conn, inputPaths);
 
     /* Tell the hooks the missing outputs that have to be copied back
        from the remote system. */
@@ -1200,7 +1200,7 @@ HookReply DerivationGoal::tryBuildHook()
             if (buildMode != bmCheck && status.known && status.known->isValid()) continue;
             missingOutputs.insert(outputName);
         }
-        WorkerProto::write(worker.store, conn, missingOutputs);
+        CommonProto::write(worker.store, conn, missingOutputs);
     }
 
     hook->sink = FdSink();

src/libstore/common-protocol-impl.hh

@@ -0,0 +1,41 @@
+#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 "common-protocol.hh"
+#include "length-prefixed-protocol-helper.hh"
+
+namespace nix {
+
+/* protocol-agnostic templates */
+
+#define COMMON_USE_LENGTH_PREFIX_SERIALISER(TEMPLATE, T) \
+    TEMPLATE T CommonProto::Serialise< T >::read(const Store & store, CommonProto::ReadConn conn) \
+    { \
+        return LengthPrefixedProtoHelper<CommonProto, T >::read(store, conn); \
+    } \
+    TEMPLATE void CommonProto::Serialise< T >::write(const Store & store, CommonProto::WriteConn conn, const T & t) \
+    { \
+        LengthPrefixedProtoHelper<CommonProto, T >::write(store, conn, t); \
+    }
+
+COMMON_USE_LENGTH_PREFIX_SERIALISER(template<typename T>, std::vector<T>)
+COMMON_USE_LENGTH_PREFIX_SERIALISER(template<typename T>, std::set<T>)
+COMMON_USE_LENGTH_PREFIX_SERIALISER(template<typename... Ts>, std::tuple<Ts...>)
+
+#define COMMA_ ,
+COMMON_USE_LENGTH_PREFIX_SERIALISER(
+    template<typename K COMMA_ typename V>,
+    std::map<K COMMA_ V>)
+#undef COMMA_
+
+
+/* protocol-specific templates */
+
+}

src/libstore/common-protocol.cc

@@ -0,0 +1,98 @@
+#include "serialise.hh"
+#include "util.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 Store & store, CommonProto::ReadConn conn)
+{
+    return readString(conn.from);
+}
+
+void CommonProto::Serialise<std::string>::write(const Store & store, CommonProto::WriteConn conn, const std::string & str)
+{
+    conn.to << str;
+}
+
+
+StorePath CommonProto::Serialise<StorePath>::read(const Store & store, CommonProto::ReadConn conn)
+{
+    return store.parseStorePath(readString(conn.from));
+}
+
+void CommonProto::Serialise<StorePath>::write(const Store & store, CommonProto::WriteConn conn, const StorePath & storePath)
+{
+    conn.to << store.printStorePath(storePath);
+}
+
+
+ContentAddress CommonProto::Serialise<ContentAddress>::read(const Store & store, CommonProto::ReadConn conn)
+{
+    return ContentAddress::parse(readString(conn.from));
+}
+
+void CommonProto::Serialise<ContentAddress>::write(const Store & store, CommonProto::WriteConn conn, const ContentAddress & ca)
+{
+    conn.to << renderContentAddress(ca);
+}
+
+
+Realisation CommonProto::Serialise<Realisation>::read(const Store & 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 Store & store, CommonProto::WriteConn conn, const Realisation & realisation)
+{
+    conn.to << realisation.toJSON().dump();
+}
+
+
+DrvOutput CommonProto::Serialise<DrvOutput>::read(const Store & store, CommonProto::ReadConn conn)
+{
+    return DrvOutput::parse(readString(conn.from));
+}
+
+void CommonProto::Serialise<DrvOutput>::write(const Store & store, CommonProto::WriteConn conn, const DrvOutput & drvOutput)
+{
+    conn.to << drvOutput.to_string();
+}
+
+
+std::optional<StorePath> CommonProto::Serialise<std::optional<StorePath>>::read(const Store & 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 Store & 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 Store & store, CommonProto::ReadConn conn)
+{
+    return ContentAddress::parseOpt(readString(conn.from));
+}
+
+void CommonProto::Serialise<std::optional<ContentAddress>>::write(const Store & store, CommonProto::WriteConn conn, const std::optional<ContentAddress> & caOpt)
+{
+    conn.to << (caOpt ? renderContentAddress(*caOpt) : "");
+}
+
+}

src/libstore/common-protocol.hh

@@ -0,0 +1,106 @@
+#pragma once
+///@file
+
+#include "serialise.hh"
+
+namespace nix {
+
+class Store;
+struct Source;
+
+// items being serialized
+class StorePath;
+struct ContentAddress;
+struct DrvOutput;
+struct Realisation;
+
+
+/**
+ * Shared serializers between the worker protocol, serve protocol, and a
+ * few others.
+ *
+ * This `struct` is basically just a `namespace`; We use a type rather
+ * than a namespace just so we can use it as a template argument.
+ */
+struct CommonProto
+{
+    /**
+     * A unidirectional read connection, to be used by the read half of the
+     * canonical serializers below.
+     */
+    struct ReadConn {
+        Source & from;
+    };
+
+    /**
+     * A unidirectional write connection, to be used by the write half of the
+     * canonical serializers below.
+     */
+    struct WriteConn {
+        Sink & to;
+    };
+
+    template<typename T>
+    struct Serialise;
+
+    /**
+     * Wrapper function around `CommonProto::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)
+    {
+        CommonProto::Serialise<T>::write(store, conn, t);
+    }
+};
+
+#define DECLARE_COMMON_SERIALISER(T) \
+    struct CommonProto::Serialise< T > \
+    { \
+        static T read(const Store & store, CommonProto::ReadConn conn); \
+        static void write(const Store & store, CommonProto::WriteConn conn, const T & str); \
+    }
+
+template<>
+DECLARE_COMMON_SERIALISER(std::string);
+template<>
+DECLARE_COMMON_SERIALISER(StorePath);
+template<>
+DECLARE_COMMON_SERIALISER(ContentAddress);
+template<>
+DECLARE_COMMON_SERIALISER(DrvOutput);
+template<>
+DECLARE_COMMON_SERIALISER(Realisation);
+
+template<typename T>
+DECLARE_COMMON_SERIALISER(std::vector<T>);
+template<typename T>
+DECLARE_COMMON_SERIALISER(std::set<T>);
+template<typename... Ts>
+DECLARE_COMMON_SERIALISER(std::tuple<Ts...>);
+
+#define COMMA_ ,
+template<typename K, typename V>
+DECLARE_COMMON_SERIALISER(std::map<K COMMA_ V>);
+#undef COMMA_
+
+/**
+ * These use the empty string for the null case, relying on the fact
+ * that the underlying types never serialize to the empty string.
+ *
+ * We do this instead of a generic std::optional<T> instance because
+ * ordinal tags (0 or 1, here) are a bit of a compatability hazard. For
+ * the same reason, we don't have a std::variant<T..> instances (ordinal
+ * tags 0...n).
+ *
+ * We could the generic instances and then these as specializations for
+ * compatability, but that's proven a bit finnicky, and also makes the
+ * worker protocol harder to implement in other languages where such
+ * specializations may not be allowed.
+ */
+template<>
+DECLARE_COMMON_SERIALISER(std::optional<StorePath>);
+template<>
+DECLARE_COMMON_SERIALISER(std::optional<ContentAddress>);
+
+}

src/libstore/derivations.cc

@@ -4,8 +4,8 @@
 #include "globals.hh"
 #include "util.hh"
 #include "split.hh"
-#include "worker-protocol.hh"
-#include "worker-protocol-impl.hh"
+#include "common-protocol.hh"
+#include "common-protocol-impl.hh"
 #include "fs-accessor.hh"
 #include <boost/container/small_vector.hpp>
 #include <nlohmann/json.hpp>
@@ -895,8 +895,8 @@ Source & readDerivation(Source & in, const Store & store, BasicDerivation & drv,
         drv.outputs.emplace(std::move(name), std::move(output));
     }
 
-    drv.inputSrcs = WorkerProto::Serialise<StorePathSet>::read(store,
-        WorkerProto::ReadConn { .from = in });
+    drv.inputSrcs = CommonProto::Serialise<StorePathSet>::read(store,
+        CommonProto::ReadConn { .from = in });
     in >> drv.platform >> drv.builder;
     drv.args = readStrings<Strings>(in);
 
@@ -944,8 +944,8 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
             },
         }, i.second.raw);
     }
-    WorkerProto::write(store,
-        WorkerProto::WriteConn { .to = out },
+    CommonProto::write(store,
+        CommonProto::WriteConn { .to = out },
         drv.inputSrcs);
     out << drv.platform << drv.builder << drv.args;
     out << drv.env.size();

src/libstore/export-import.cc

@@ -1,8 +1,8 @@
 #include "serialise.hh"
 #include "store-api.hh"
 #include "archive.hh"
-#include "worker-protocol.hh"
-#include "worker-protocol-impl.hh"
+#include "common-protocol.hh"
+#include "common-protocol-impl.hh"
 
 #include <algorithm>
 
@@ -46,8 +46,8 @@ void Store::exportPath(const StorePath & path, Sink & sink)
     teeSink
         << exportMagic
         << printStorePath(path);
-    WorkerProto::write(*this,
-        WorkerProto::WriteConn { .to = teeSink },
+    CommonProto::write(*this,
+        CommonProto::WriteConn { .to = teeSink },
         info->references);
     teeSink
         << (info->deriver ? printStorePath(*info->deriver) : "")
@@ -76,8 +76,8 @@ StorePaths Store::importPaths(Source & source, CheckSigsFlag checkSigs)
 
         //Activity act(*logger, lvlInfo, "importing path '%s'", info.path);
 
-        auto references = WorkerProto::Serialise<StorePathSet>::read(*this,
-            WorkerProto::ReadConn { .from = source });
+        auto references = CommonProto::Serialise<StorePathSet>::read(*this,
+            CommonProto::ReadConn { .from = source });
         auto deriver = readString(source);
         auto narHash = hashString(htSHA256, saved.s);