servers: implement consistent error handling policy for coro_* functions

- coro_ read function returns empty unique_ptr on error
- coro_ write functions close socket on error
- caller does need only to handle empty unique_ptr from reads, generally
  with immediate return

src/server/campaignd/server.cpp

@@ -1153,11 +1153,9 @@ void server::handle_request_campaign(const server::request& req)
 
 			LOG_CS << req << "Sending add-on '" << name << "' version: " << from << " -> " << to << " (delta)\n";
 
-			if(utils::visit([this, &req, &doc](auto && sock) {
-				boost::system::error_code ec;
-				coro_send_doc(sock, doc, req.yield[ec]);
-				return check_error(ec, sock);
-			}, req.sock)) return;
+			utils::visit([this, &req, &doc](auto && sock) {
+				coro_send_doc(sock, doc, req.yield);
+			}, req.sock);
 
 			full_pack_path.clear();
 		}
@@ -1173,11 +1171,9 @@ void server::handle_request_campaign(const server::request& req)
 		}
 
 		LOG_CS << req << "Sending add-on '" << name << "' version: " << to << " size: " << full_pack_size / 1024 << " KiB\n";
-		if(utils::visit([this, &req, &full_pack_path](auto&& socket) {
-			boost::system::error_code ec;
-			coro_send_file(socket, full_pack_path, req.yield[ec]);
-			return check_error(ec, socket);
-		}, req.sock)) return;
+		utils::visit([this, &req, &full_pack_path](auto&& socket) {
+			coro_send_file(socket, full_pack_path, req.yield);
+		}, req.sock);
 	}
 
 	// Clients doing upgrades or some other specific thing shouldn't bump
@@ -1229,11 +1225,9 @@ void server::handle_request_campaign_hash(const server::request& req)
 		}
 
 		LOG_CS << req << "Sending add-on hash index for '" << req.cfg["name"] << "' size: " << file_size / 1024 << " KiB\n";
-		if(utils::visit([this, &path, &req](auto&& socket) {
-			boost::system::error_code ec;
-			coro_send_file(socket, path, req.yield[ec]);
-			return check_error(ec, socket);
-		}, req.sock)) return;
+		utils::visit([this, &path, &req](auto&& socket) {
+			coro_send_file(socket, path, req.yield);
+		}, req.sock);
 	}
 }
 

src/server/common/server_base.cpp

@@ -347,7 +347,10 @@ template<class SocketPtr> void coro_send_file_userspace(SocketPtr socket, const
 
 	boost::system::error_code ec;
 	async_write(*socket, boost::asio::buffer(data_size.buf), yield[ec]);
-	if(check_error(ec, socket)) return;
+	if(check_error(ec, socket)) {
+		socket->lowest_layer().close();
+		return;
+	}
 
 	auto ifs { filesystem::istream_file(filename) };
 	ifs->seekg(0);
@@ -355,7 +358,10 @@ template<class SocketPtr> void coro_send_file_userspace(SocketPtr socket, const
 		char buf[16384];
 		ifs->read(buf, sizeof(buf));
 		async_write(*socket, boost::asio::buffer(buf, ifs->gcount()), yield[ec]);
-		if(check_error(ec, socket)) return;
+		if(check_error(ec, socket)) {
+			socket->lowest_layer().close();
+			return;
+		}
 	}
 }
 

src/server/common/server_base.hpp

@@ -104,6 +104,7 @@ public:
 	 * Receive WML document from a coroutine
 	 * @param socket
 	 * @param yield The function will suspend on read operation using this yield context
+	 * @return unique_ptr with doc deceived. In case of error empty unique_ptr
 	 */
 	template<class SocketPtr> std::unique_ptr<simple_wml::document> coro_receive_doc(SocketPtr socket, boost::asio::yield_context yield);
 

src/server/wesnothd/server.cpp

@@ -683,13 +683,10 @@ void server::handle_new_client(tls_socket_ptr socket)
 template<class SocketPtr>
 void server::login_client(boost::asio::yield_context yield, SocketPtr socket)
 {
-	boost::system::error_code ec;
+	coro_send_doc(socket, version_query_response_, yield);
 
-	coro_send_doc(socket, version_query_response_, yield[ec]);
-	if(check_error(ec, socket)) return;
-
-	auto doc { coro_receive_doc(socket, yield[ec]) };
-	if(check_error(ec, socket) || !doc) return;
+	auto doc { coro_receive_doc(socket, yield) };
+	if(!doc) return;
 
 	std::string client_version, client_source;
 	if(const simple_wml::node* const version = doc->child("version")) {
@@ -706,8 +703,7 @@ void server::login_client(boost::asio::yield_context yield, SocketPtr socket)
 		if(accepted_it != accepted_versions_.end()) {
 			LOG_SERVER << log_address(socket) << "\tplayer joined using accepted version " << client_version
 					   << ":\ttelling them to log in.\n";
-			coro_send_doc(socket, login_response_, yield[ec]);
-			if(check_error(ec, socket)) return;
+			coro_send_doc(socket, login_response_, yield);
 		} else {
 			simple_wml::document response;
 
@@ -748,8 +744,8 @@ void server::login_client(boost::asio::yield_context yield, SocketPtr socket)
 	bool registered, is_moderator;
 
 	while(true) {
-		auto login_response { coro_receive_doc(socket, yield[ec]) };
-		if(check_error(ec, socket) || !login_response) return;
+		auto login_response { coro_receive_doc(socket, yield) };
+		if(!login_response) return;
 
 		if(const simple_wml::node* const login = login_response->child("login")) {
 			username = (*login)["username"].to_string();
@@ -765,8 +761,7 @@ void server::login_client(boost::asio::yield_context yield, SocketPtr socket)
 	simple_wml::document join_lobby_response;
 	join_lobby_response.root().add_child("join_lobby").set_attr("is_moderator", is_moderator ? "yes" : "no");
 	join_lobby_response.root().child("join_lobby")->set_attr_dup("profile_url_prefix", "https://r.wesnoth.org/u");
-	coro_send_doc(socket, join_lobby_response, yield[ec]);
-	if(check_error(ec, socket)) return;
+	coro_send_doc(socket, join_lobby_response, yield);
 
 	simple_wml::node& player_cfg = games_and_users_list_.root().add_child("user");
 	wesnothd::player new_player(
@@ -1100,8 +1095,8 @@ template<class SocketPtr> void server::handle_player(boost::asio::yield_context
 
 	while(true) {
 		boost::system::error_code ec;
-		auto doc { coro_receive_doc(socket, yield[ec]) };
-		if(check_error(ec, socket) || !doc) return;
+		auto doc { coro_receive_doc(socket, yield) };
+		if(!doc) return;
 
 		// DBG_SERVER << client_address(socket) << "\tWML received:\n" << doc->output() << std::endl;
 		if(doc->child("refresh_lobby")) {