netplay: more strict checks for error codes from socket operations

lib/netplay/netsocket.cpp

@@ -72,7 +72,7 @@ struct Socket
 
 	SOCKET fd[SOCK_COUNT];
 	bool ready;
-	std::error_code writeErrorCode = make_network_error_code(0);
+	optional<std::error_code> writeErrorCode = nullopt;
 	bool deleteLater;
 	char textAddress[40] = {};
 
@@ -650,9 +650,9 @@ net::result<ssize_t> writeAll(Socket& sock, const void *buf, size_t size, size_t
 		return tl::make_unexpected(make_network_error_code(EBADF));
 	}
 
-	if (sock.writeErrorCode)
+	if (sock.writeErrorCode.has_value())
 	{
-		return tl::make_unexpected(sock.writeErrorCode);
+		return tl::make_unexpected(sock.writeErrorCode.value());
 	}
 
 	if (size > 0)
@@ -731,7 +731,7 @@ void socketFlush(Socket& sock, uint8_t player, size_t *rawByteCount)
 		return;  // Not compressed, so don't mess with zlib.
 	}
 
-	ASSERT(!sock.writeErrorCode, "Socket write error?? (Player: %" PRIu8 "", player);
+	ASSERT(!sock.writeErrorCode.has_value(), "Socket write error?? (Player: %" PRIu8 "", player);
 
 	// Flush data out of zlib compression state.
 	do

lib/netplay/netsocket.h

@@ -26,6 +26,9 @@
 #include <system_error>
 #include <vector>
 
+#include <nonstd/optional.hpp>
+using nonstd::optional;
+using nonstd::nullopt;
 #include <tl/expected.hpp>
 
 namespace net
@@ -137,7 +140,6 @@ int checkSockets(const SocketSet& set, unsigned int timeout); ///< Checks which
 // Higher-level functions for opening a connection / socket
 struct OpenConnectionResult
 {
-public:
 	OpenConnectionResult(std::error_code ec, std::string errorString)
 	: errorCode(ec)
 	, errorString(errorString)
@@ -146,19 +148,19 @@ struct OpenConnectionResult
 	OpenConnectionResult(Socket* open_socket)
 	: open_socket(open_socket)
 	{ }
-public:
-	bool hasError() const { return static_cast<bool>(errorCode); }
-public:
+
+	bool hasError() const { return errorCode.has_value(); }
+
 	OpenConnectionResult( const OpenConnectionResult& other ) = delete; // non construction-copyable
 	OpenConnectionResult& operator=( const OpenConnectionResult& ) = delete; // non copyable
 	OpenConnectionResult(OpenConnectionResult&&) = default;
 	OpenConnectionResult& operator=(OpenConnectionResult&&) = default;
-public:
+
 	struct SocketDeleter {
 		void operator()(Socket* b) { if (b) { socketClose(b); } }
 	};
 	std::unique_ptr<Socket, SocketDeleter> open_socket;
-	std::error_code errorCode;
+	optional<std::error_code> errorCode = nullopt;
 	std::string errorString;
 };
 typedef std::function<void (OpenConnectionResult&& result)> OpenConnectionToHostResultCallback;

src/screens/joiningscreen.cpp

@@ -1149,8 +1149,9 @@ void WzJoiningGameScreen_HandlerRoot::processOpenConnectionResult(size_t connect
 		{
 			debug(LOG_ERROR, "%s", result.errorString.c_str());
 			// Done trying connections - all failed
-			const auto sockErrorMsg = result.errorCode.message();
-			auto localizedError = astringf(_("Failed to open connection: [%d] %s"), result.errorCode.value(), sockErrorMsg.c_str());
+			const auto errCode = result.errorCode.value();
+			const auto sockErrorMsg = errCode.message();
+			auto localizedError = astringf(_("Failed to open connection: [%d] %s"), errCode.value(), sockErrorMsg.c_str());
 			handleFailure(FailureDetails::makeFromInternalError(WzString::fromUtf8(localizedError)));
 		}
 		return;