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Revert "Revert "Use template structs instead of phantoms""

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This is the more typically way to do [Argument-dependent
lookup](https://en.cppreference.com/w/cpp/language/adl)-leveraging
generic serializers in C++. It makes the relationship between the `read`
and `write` methods more clear and rigorous, and also looks more
familiar to users coming from other languages that do not have C++'s
libertine ad-hoc overloading.

I am returning to this because during the review in
https://github.com/NixOS/nix/pull/6223, it came up as something that
would make the code easier to read --- easier today hopefully already,
but definitely easier if we were have multiple codified protocols with
code sharing between them as that PR seeks to accomplish.

If I recall correctly, the main criticism of this the first time around
(in 2020) was that having to specify the type when writing, e.g.
`WorkerProto<MyType>::write`, was too verbose and cumbersome. This is
now addressed with the `workerProtoWrite` wrapper function.

This method is also the way `nlohmann::json`, which we have used for a
number of years now, does its serializers, for what its worth.

This reverts commit 45a0ed82f0. That
commit in turn reverted 9ab07e99f5.
This commit is contained in:
John Ericson 2023-05-17 22:04:59 -04:00
parent 684e9be8b9
commit cb5052d98f
10 changed files with 182 additions and 151 deletions
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58
src/libstore/worker-protocol.cc
View file

@ -9,31 +9,31 @@
#include <nlohmann/json.hpp>
namespace nix::worker_proto {
namespace nix {
std::string read(const Store & store, Source & from, Phantom<std::string> _)
std::string WorkerProto<std::string>::read(const Store & store, Source & from)
{
return readString(from);
}
void write(const Store & store, Sink & out, const std::string & str)
void WorkerProto<std::string>::write(const Store & store, Sink & out, const std::string & str)
{
out << str;
}
StorePath read(const Store & store, Source & from, Phantom<StorePath> _)
StorePath WorkerProto<StorePath>::read(const Store & store, Source & from)
{
return store.parseStorePath(readString(from));
}
void write(const Store & store, Sink & out, const StorePath & storePath)
void WorkerProto<StorePath>::write(const Store & store, Sink & out, const StorePath & storePath)
{
out << store.printStorePath(storePath);
}
std::optional<TrustedFlag> read(const Store & store, Source & from, Phantom<std::optional<TrustedFlag>> _)
std::optional<TrustedFlag> WorkerProto<std::optional<TrustedFlag>>::read(const Store & store, Source & from)
{
auto temp = readNum<uint8_t>(from);
switch (temp) {
@ -48,7 +48,7 @@ std::optional<TrustedFlag> read(const Store & store, Source & from, Phantom<std:
}
}
void write(const Store & store, Sink & out, const std::optional<TrustedFlag> & optTrusted)
void WorkerProto<std::optional<TrustedFlag>>::write(const Store & store, Sink & out, const std::optional<TrustedFlag> & optTrusted)
{
if (!optTrusted)
out << (uint8_t)0;
@ -67,30 +67,30 @@ void write(const Store & store, Sink & out, const std::optional<TrustedFlag> & o
}
ContentAddress read(const Store & store, Source & from, Phantom<ContentAddress> _)
ContentAddress WorkerProto<ContentAddress>::read(const Store & store, Source & from)
{
return ContentAddress::parse(readString(from));
}
void write(const Store & store, Sink & out, const ContentAddress & ca)
void WorkerProto<ContentAddress>::write(const Store & store, Sink & out, const ContentAddress & ca)
{
out << renderContentAddress(ca);
}
DerivedPath read(const Store & store, Source & from, Phantom<DerivedPath> _)
DerivedPath WorkerProto<DerivedPath>::read(const Store & store, Source & from)
{
auto s = readString(from);
return DerivedPath::parseLegacy(store, s);
}
void write(const Store & store, Sink & out, const DerivedPath & req)
void WorkerProto<DerivedPath>::write(const Store & store, Sink & out, const DerivedPath & req)
{
out << req.to_string_legacy(store);
}
Realisation read(const Store & store, Source & from, Phantom<Realisation> _)
Realisation WorkerProto<Realisation>::read(const Store & store, Source & from)
{
std::string rawInput = readString(from);
return Realisation::fromJSON(
@ -99,41 +99,41 @@ Realisation read(const Store & store, Source & from, Phantom<Realisation> _)
);
}
void write(const Store & store, Sink & out, const Realisation & realisation)
void WorkerProto<Realisation>::write(const Store & store, Sink & out, const Realisation & realisation)
{
out << realisation.toJSON().dump();
}
DrvOutput read(const Store & store, Source & from, Phantom<DrvOutput> _)
DrvOutput WorkerProto<DrvOutput>::read(const Store & store, Source & from)
{
return DrvOutput::parse(readString(from));
}
void write(const Store & store, Sink & out, const DrvOutput & drvOutput)
void WorkerProto<DrvOutput>::write(const Store & store, Sink & out, const DrvOutput & drvOutput)
{
out << drvOutput.to_string();
}
KeyedBuildResult read(const Store & store, Source & from, Phantom<KeyedBuildResult> _)
KeyedBuildResult WorkerProto<KeyedBuildResult>::read(const Store & store, Source & from)
{
auto path = read(store, from, Phantom<DerivedPath> {});
auto br = read(store, from, Phantom<BuildResult> {});
auto path = WorkerProto<DerivedPath>::read(store, from);
auto br = WorkerProto<BuildResult>::read(store, from);
return KeyedBuildResult {
std::move(br),
/* .path = */ std::move(path),
};
}
void write(const Store & store, Sink & to, const KeyedBuildResult & res)
void WorkerProto<KeyedBuildResult>::write(const Store & store, Sink & to, const KeyedBuildResult & res)
{
write(store, to, res.path);
write(store, to, static_cast<const BuildResult &>(res));
workerProtoWrite(store, to, res.path);
workerProtoWrite(store, to, static_cast<const BuildResult &>(res));
}
BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
BuildResult WorkerProto<BuildResult>::read(const Store & store, Source & from)
{
BuildResult res;
res.status = (BuildResult::Status) readInt(from);
@ -143,7 +143,7 @@ BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
>> res.isNonDeterministic
>> res.startTime
>> res.stopTime;
auto builtOutputs = read(store, from, Phantom<DrvOutputs> {});
auto builtOutputs = WorkerProto<DrvOutputs>::read(store, from);
for (auto && [output, realisation] : builtOutputs)
res.builtOutputs.insert_or_assign(
std::move(output.outputName),
@ -151,7 +151,7 @@ BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
return res;
}
void write(const Store & store, Sink & to, const BuildResult & res)
void WorkerProto<BuildResult>::write(const Store & store, Sink & to, const BuildResult & res)
{
to
<< res.status
@ -163,28 +163,28 @@ void write(const Store & store, Sink & to, const BuildResult & res)
DrvOutputs builtOutputs;
for (auto & [output, realisation] : res.builtOutputs)
builtOutputs.insert_or_assign(realisation.id, realisation);
write(store, to, builtOutputs);
workerProtoWrite(store, to, builtOutputs);
}
std::optional<StorePath> read(const Store & store, Source & from, Phantom<std::optional<StorePath>> _)
std::optional<StorePath> WorkerProto<std::optional<StorePath>>::read(const Store & store, Source & from)
{
auto s = readString(from);
return s == "" ? std::optional<StorePath> {} : store.parseStorePath(s);
}
void write(const Store & store, Sink & out, const std::optional<StorePath> & storePathOpt)
void WorkerProto<std::optional<StorePath>>::write(const Store & store, Sink & out, const std::optional<StorePath> & storePathOpt)
{
out << (storePathOpt ? store.printStorePath(*storePathOpt) : "");
}
std::optional<ContentAddress> read(const Store & store, Source & from, Phantom<std::optional<ContentAddress>> _)
std::optional<ContentAddress> WorkerProto<std::optional<ContentAddress>>::read(const Store & store, Source & from)
{
return ContentAddress::parseOpt(readString(from));
}
void write(const Store & store, Sink & out, const std::optional<ContentAddress> & caOpt)
void WorkerProto<std::optional<ContentAddress>>::write(const Store & store, Sink & out, const std::optional<ContentAddress> & caOpt)
{
out << (caOpt ? renderContentAddress(*caOpt) : "");
}