coro_app.cpp

#include <drogon/drogon.h>
#include <exception>
#include <coroutine>
#include <stdexcept>

using namespace drogon;

int main()
{
	app().createDbClient("postgresql", "localhost", 5432, "test", "test", "some legit password 191561", 16)
		.addListener("0.0.0.0", 4444)
		.setThreadNum(1);
	

	// Asking DB for data then reply (table only as 1 row)
	//
	// NOTE: Variables must be passed by value. Otherwise (references) can easily go out of scope. Since the function(subrutine) can 
	//       exit while the coroutine is executing.
	// NOTE: Must return a `promise_type`. Otherwise C++ doesn't see it as coroutine
	//
	// Performance: 7244.49 Q/s (98.32%)
	// 1 Server thread and 4 client thread. CPU: Cortex-A72 @ 2GHz
	// Benchmarked using ApacheBanchmark. Average over 100K requests
	//
	// It fluctuate a bit. Overall, coroutine is a bit slower than callback.
	app().registerHandler("/coro", [](HttpRequestPtr req, std::function<void (const HttpResponsePtr &)> callback) -> AsyncTask {
		auto sql = app().getDbClient();

		// Coroutines! YAY!!!
		auto result = co_await sql->execSqlCoro("SELECT * FROM users;");
		//^^^^^ Copy by value kills the just-created coroutine frame. Somehow this made things faster then by reference
		auto resp = HttpResponse::newHttpResponse();
		callback(resp);
	});

	// The current solution of using callbacks
	//
	// Performance: 7367.88Q/s (100%)
	app().registerHandler("/cb", [](const HttpRequestPtr& req, std::function<void (const HttpResponsePtr &)> &&callback) -> void{
		auto sql = app().getDbClient();
		sql->execSqlAsync("SELECT * FROM users", [callback](const drogon::orm::Result& result) {
			auto resp = HttpResponse::newHttpResponse();
			callback(resp);
		}, [](const drogon::orm::DrogonDbException& e){
		});
	});

	// ==================================================================================================================
	// Misc tests
	
	// Make sure the awaiter is written correctly to propergrate exceptions from callback into coroutine
	app().registerHandler("/coro_bad_sql", [](HttpRequestPtr req, std::function<void (const HttpResponsePtr &)> callback) -> AsyncTask {
		auto sql = app().getDbClient();
		try {
			auto result = co_await sql->execSqlCoro("SELECT * FROM users WHERE username ============ ?;");
			throw std::logic_error("This line shouldn't run because of exceptions");
		}
		catch(const drogon::orm::Failure& e) {
			auto resp = HttpResponse::newHttpResponse();
			resp->setBody("Exception is cought");
			callback(resp);
		}
	});


	// Make sure SQL with parameters work
	app().registerHandler("/coro_with_param", [](HttpRequestPtr req, std::function<void (const HttpResponsePtr &)> callback) -> AsyncTask {
		auto sql = app().getDbClient();
		auto result = co_await sql->execSqlCoro("select * from users where username = $1 limit $2;", "the_user", 1);
		auto resp = HttpResponse::newHttpResponse();
		callback(resp);
	});

	app().registerHandler("/test_request_coro", [](HttpRequestPtr req, std::function<void (const HttpResponsePtr &)> callback) -> AsyncTask {
		auto client = HttpClient::newHttpClient("http://example.com");
		auto example_req = HttpRequest::newHttpRequest();
		example_req->setPath("/");

		try {
			auto example_resp = co_await client->sendRequestCoro(example_req);
			if(example_resp->getBody().size() == 0)
				throw std::runtime_error("Why is there nothing");
		}
		catch(const std::exception& e) {
			std::cerr << "Error in request: " << e.what() << std::endl;
		}
		auto resp = HttpResponse::newHttpResponse();
		callback(resp);
	});

	app().run();
}