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file-transfer-server.cpp
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file-transfer-server.cpp
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// Copyright 2024 Dennis Hezel
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "buffer.hpp"
#include "example/v1/example.grpc.pb.h"
#include "example/v1/example_ext.grpc.pb.h"
#include "helper.hpp"
#include "rethrow_first_arg.hpp"
#include "scope_guard.hpp"
#include "server_shutdown_asio.hpp"
#include <agrpc/asio_grpc.hpp>
#include <boost/asio/bind_executor.hpp>
#include <boost/asio/co_spawn.hpp>
#include <boost/asio/experimental/parallel_group.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/asio/stream_file.hpp>
#include <boost/asio/write.hpp>
#include <grpcpp/server.h>
#include <grpcpp/server_builder.h>
#include <filesystem>
#include <fstream>
#include <optional>
#include <thread>
namespace asio = boost::asio;
// begin-snippet: server-side-file-transfer
// ---------------------------------------------------
// Example showing how to transfer files over a streaming RPC. Stack buffers are used to customize memory allocation.
// ---------------------------------------------------
// end-snippet
using RPC = agrpc::ServerRPC<&example::v1::ExampleExt::AsyncService::RequestSendFile>;
inline constexpr asio::use_awaitable_t<agrpc::GrpcExecutor> USE_AWAITABLE{};
// The use of ` asio::awaitable<bool, agrpc::GrpcExecutor>` is not required but `agrpc::GrpcExecutor` is slightly
// smaller and faster to copy than the `asio::any_io_executor` of the default `asio::awaitable`.
asio::awaitable<bool, agrpc::GrpcExecutor> handle_send_file_request(asio::io_context& io_context, RPC& rpc,
const std::string& file_path)
{
// These buffers are used to customize allocation of completion handlers.
example::Buffer<308> buffer1;
example::Buffer<40> buffer2;
example::v1::SendFileRequest first_buffer;
// Read the first chunk from the client
bool ok = co_await rpc.read(first_buffer, buffer1.bind_allocator(USE_AWAITABLE));
if (!ok)
{
// Client hung up
co_await rpc.finish({}, grpc::Status::OK, buffer1.bind_allocator(USE_AWAITABLE));
co_return false;
}
example::v1::SendFileRequest second_buffer;
// Switch to the io_context and open the file there to avoid blocking the GrpcContext.
co_await asio::post(buffer1.bind_allocator(asio::bind_executor(io_context, USE_AWAITABLE)));
// Relying on CTAD here to create a `asio::basic_stream_file<asio::io_context::executor_type>` which is slightly
// more performant than the default `asio::stream_file` that is templated on `asio::any_io_executor`.
//
// If you get exception: io_uring_queue_init: Cannot allocate memory [system:12]
// here then run `ulimit -l 65535`, see also https://github.com/axboe/liburing/issues/157
asio::basic_stream_file file{io_context.get_executor(), file_path,
asio::stream_file::write_only | asio::stream_file::create};
// Lambda that writes the first argument to the file and simultaneously waits for the next message from the client.
const auto write_and_read =
[&](const example::v1::SendFileRequest& message_to_write, example::v1::SendFileRequest& message_to_read)
{
return asio::experimental::make_parallel_group(
[&](auto&& token)
{
// Using bind_executor to avoid switching contexts in case this function completes after
// agrpc::read.
return asio::async_write(
file, asio::buffer(message_to_write.content()),
buffer1.bind_allocator(asio::bind_executor(asio::system_executor{}, std::move(token))));
},
[&](auto&& token)
{
// Need to bind_executor here because `token` is a simple invocable without an
// associated executor.
return rpc.read(message_to_read, buffer2.bind_allocator(std::move(token)));
})
.async_wait(asio::experimental::wait_for_all(), buffer1.bind_allocator(USE_AWAITABLE));
};
auto* current = &first_buffer;
auto* next = &second_buffer;
while (ok)
{
auto [completion_order, ec, bytes_written, next_ok] = co_await write_and_read(*current, *next);
if (ec)
{
throw boost::system::system_error(ec);
}
ok = next_ok;
std::swap(current, next);
}
co_return co_await rpc.finish({}, grpc::Status::OK, buffer1.bind_allocator(USE_AWAITABLE));
}
void run_io_context(asio::io_context& io_context)
{
try
{
io_context.run();
}
catch (const std::exception& e)
{
std::cerr << "Exception from io_context: " << e.what() << std::endl;
std::abort();
}
}
int main(int argc, const char** argv)
{
const auto port = argc >= 2 ? argv[1] : "50051";
const auto host = std::string("0.0.0.0:") + port;
example::v1::ExampleExt::AsyncService service_ext;
std::unique_ptr<grpc::Server> server;
grpc::ServerBuilder builder;
agrpc::GrpcContext grpc_context{builder.AddCompletionQueue()};
builder.AddListeningPort(host, grpc::InsecureServerCredentials());
builder.RegisterService(&service_ext);
server = builder.BuildAndStart();
abort_if_not(bool{server});
example::ServerShutdown shutdown{*server, grpc_context};
asio::io_context io_context{1};
std::optional guard{asio::require(io_context.get_executor(), asio::execution::outstanding_work_t::tracked)};
try
{
// Prepare output file
const auto temp_dir = argc >= 3 ? std::filesystem::path{argv[2]} : std::filesystem::temp_directory_path();
const auto file_path = (temp_dir / "file-transfer-output.txt").string();
std::filesystem::remove(file_path);
agrpc::register_awaitable_rpc_handler<RPC>(
grpc_context, service_ext,
[&](RPC& rpc) -> asio::awaitable<void, agrpc::GrpcExecutor>
{
abort_if_not(co_await handle_send_file_request(io_context, rpc, file_path));
shutdown.shutdown();
},
example::RethrowFirstArg{});
std::thread io_context_thread{&run_io_context, std::ref(io_context)};
example::ScopeGuard on_exit{[&]
{
guard.reset();
io_context_thread.join();
}};
grpc_context.run();
// Check that output file has the expected content
std::string content;
{
std::ifstream stream{file_path};
stream.exceptions(std::ifstream::failbit);
stream >> content;
}
abort_if_not("content" == content);
}
catch (const std::exception& e)
{
std::cerr << "Exception: " << e.what() << std::endl;
return 1;
}
return 0;
}