[clangd][remote] Add flag to set idletimeout

[kadircet]

Summary

By default gRPC has no idletimeout and some firewalls might drop idle
connections after a certain period. This results in idle clients
shouting into void until server resets the connection.

[sammccall]

clang-tools-extra/clangd/index/remote/server/Server.cpp

84

10 seems much too low, maybe set this to 5 min or so?
Going idle for a minute or so seems common, and the only real reason we have to time connections out is to beat the gcp firewall. So I don't see the need to be really aggressive here.

[kadircet]

Change 10 seconds to 600 seconds.

clang-tools-extra/clangd/index/remote/server/Server.cpp

84

oops this was meant to be 10 minutes, not seconds :D

[sammccall]

clang-tools-extra/clangd/index/remote/server/Server.cpp

84

Haha, makes more sense :-)

Setting this to exactly the gcp timeout seems tempting fate with hard to debug races. Maybe 8 min?

[kadircet]

• change default from 10 to 8 minutes

[kadircet]

clang-tools-extra/clangd/index/remote/server/Server.cpp

84

fair point, done!

clang-tools-extra/clangd/index/remote/server/Server.cpp

 //===--- Server.cpp - gRPC-based Remote Index Server  ---------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Index.pb.h"
 #include "Service.grpc.pb.h"
 #include "index/Index.h"
 #include "index/Serialization.h"
 #include "index/Symbol.h"
 #include "index/remote/marshalling/Marshalling.h"
 #include "support/Context.h"
 #include "support/Logger.h"
 #include "support/Shutdown.h"
llvm::cl::opt<bool> PrettyPrint{
     llvm::cl::desc("Pretty-print JSON output in the trace"),
     llvm::cl::init(false),
 };
 
 llvm::cl::opt<std::string> ServerAddress(
     "server-address", llvm::cl::init("0.0.0.0:50051"),
     llvm::cl::desc("Address of the invoked server. Defaults to 0.0.0.0:50051"));
 
+llvm::cl::opt<size_t> IdleTimeoutSeconds(
+    "idle-timeout", llvm::cl::init(10),
+    llvm::cl::desc("Maximum time a channel may stay idle until server closes "
+                   "the connection, in seconds. Defaults to 10."));
+
 static Key<grpc::ServerContext *> CurrentRequest;
 
 class RemoteIndexServer final : public v1::SymbolIndex::Service {
 public:
   RemoteIndexServer(clangd::SymbolIndex &Index, llvm::StringRef IndexRoot)
       : Index(Index) {
     llvm::SmallString<256> NativePath = IndexRoot;
     llvm::sys::path::native(NativePath);

 void runServerAndWait(clangd::SymbolIndex &Index, llvm::StringRef ServerAddress,
                       llvm::StringRef IndexPath) {
   RemoteIndexServer Service(Index, IndexRoot);
 
   grpc::EnableDefaultHealthCheckService(true);
   grpc::ServerBuilder Builder;
   Builder.AddListeningPort(ServerAddress.str(),
                            grpc::InsecureServerCredentials());
+  Builder.AddChannelArgument(GRPC_ARG_MAX_CONNECTION_IDLE_MS,
+                             IdleTimeoutSeconds * 1000);
   Builder.RegisterService(&Service);
   std::unique_ptr<grpc::Server> Server(Builder.BuildAndStart());
   log("Server listening on {0}", ServerAddress);
 
   std::thread ServerShutdownWatcher([&]() {
     static constexpr auto WatcherFrequency = std::chrono::seconds(5);
     while (!clang::clangd::shutdownRequested())
       std::this_thread::sleep_for(WatcherFrequency);