showcasing the elegance of asyncio's concurrent programming model:

asyncio::task::Task<void> asyncMain(const int argc, char *argv[]) {
auto client = Client::make("localhost:50051");

co_await all(
// Unary RPC
asyncio::task::spawn([&]() -> asyncio::task::Task<void> {
sample::EchoRequest req;
req.set_message("Hello gRPC!");
const auto resp = co_await client.echo(req);
fmt::print("Echo: {}\n", resp.message());
}),

// Server streaming + client streaming, connected via a channel
asyncio::task::spawn([&]() -> asyncio::task::Task<void> {
sample::GetNumbersRequest req;
req.set_value(1);
req.set_count(5);

auto [sender, receiver] = asyncio::channel<sample::Number>();

const auto result = co_await all(
client.getNumbers(req, std::move(sender)),
client.sum(std::move(receiver))
);

const auto &resp = std::get<sample::SumResponse>(result);
fmt::print("Sum: {}, count: {}\n", resp.total(), resp.count());
}),

// Bidirectional streaming
asyncio::task::spawn([&]() -> asyncio::task::Task<void> {
auto [inSender, inReceiver] = asyncio::channel<sample::ChatMessage>();
auto [outSender, outReceiver] = asyncio::channel<sample::ChatMessage>();

co_await all(
client.chat(std::move(outReceiver), std::move(inSender)),
asyncio::task::spawn([&]() -> asyncio::task::Task<void> {
sample::ChatMessage msg;
msg.set_content("Hello server!");
co_await asyncio::error::guard(outSender.send(std::move(msg)));
outSender.close();
}),
asyncio::task::spawn([&]() -> asyncio::task::Task<void> {
const auto msg = co_await asyncio::error::guard(inReceiver.receive());
fmt::print("Chat reply: {}\n", msg.content());
})
);
})
);
}

The channel-based pipeline connecting `getNumbers` and `sum` is especially worth noting: numbers produced by the server-streaming RPC flow directly through the channel into the client-streaming RPC. The whole pipeline looks like synchronous code, but is fully asynchronous underneath.

> Full source code: [GitHub](https://github.com/Hackerl/asyncio/tree/master/sample/grpc)
> Due to word count limitations, the server-side section can only be placed in Part 2.

https://redd.it/1ssjrsx
@r_cpp