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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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16
src/libstore/legacy-ssh-store.cc
View file

@ -146,7 +146,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
auto deriver = readString(conn->from);
if (deriver != "")
info->deriver = parseStorePath(deriver);
info->references = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
info->references = WorkerProto<StorePathSet>::read(*this, conn->from);
readLongLong(conn->from); // download size
info->narSize = readLongLong(conn->from);
@ -180,7 +180,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
<< printStorePath(info.path)
<< (info.deriver ? printStorePath(*info.deriver) : "")
<< info.narHash.to_string(Base16, false);
worker_proto::write(*this, conn->to, info.references);
workerProtoWrite(*this, conn->to, info.references);
conn->to
<< info.registrationTime
<< info.narSize
@ -209,7 +209,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
conn->to
<< exportMagic
<< printStorePath(info.path);
worker_proto::write(*this, conn->to, info.references);
workerProtoWrite(*this, conn->to, info.references);
conn->to
<< (info.deriver ? printStorePath(*info.deriver) : "")
<< 0
@ -294,7 +294,7 @@ public:
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 = worker_proto::read(*this, conn->from, Phantom<DrvOutputs> {});
auto builtOutputs = WorkerProto<DrvOutputs>::read(*this, conn->from);
for (auto && [output, realisation] : builtOutputs)
status.builtOutputs.insert_or_assign(
std::move(output.outputName),
@ -358,10 +358,10 @@ public:
conn->to
<< cmdQueryClosure
<< includeOutputs;
worker_proto::write(*this, conn->to, paths);
workerProtoWrite(*this, conn->to, paths);
conn->to.flush();
for (auto & i : worker_proto::read(*this, conn->from, Phantom<StorePathSet> {}))
for (auto & i : WorkerProto<StorePathSet>::read(*this, conn->from))
out.insert(i);
}
@ -374,10 +374,10 @@ public:
<< cmdQueryValidPaths
<< false // lock
<< maybeSubstitute;
worker_proto::write(*this, conn->to, paths);
workerProtoWrite(*this, conn->to, paths);
conn->to.flush();
return worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
return WorkerProto<StorePathSet>::read(*this, conn->from);
}
void connect() override