Feature: use Happy Eyeballs to make network connections (TCP-only) (#9199)

Hostnames like "content.openttd.org" resolve into multiple IPv4 and IPv6.
It is possible that either of the IPs is not working, either due to
a poorly configured OS (having IPv6 but no valid route), broken network
paths, or a service that is temporary unavailable.

Instead of trying the IPs one by one, waiting for a 3s timeout between
each, be a bit more like browsers, and stack attempts on top of each
other with slight delays. This is called Happy Eyebells.

Initially, try the first IPv6 address. If within 250ms there is no
connection yet, try the first IPv4 address. 250ms later, try the
second IPv6 address, etc, till all addresses are tried.

If any connection is created, abort all the other (pending) connections
and use the one that is created. If all fail 3s after the last connect(),
trigger a timeout for all.

1 files changed, 29 insertions, 12 deletions

diff --git a/src/network/network.cpp b/src/network/network.cpp
index 83a93a22e..bbf6bb5de 100644
--- a/src/network/network.cpp
+++ b/src/network/network.cpp
@@ -502,6 +502,19 @@ std::string_view ParseFullConnectionString(const std::string &connection_string,
 }
 
 /**
+ * Normalize a connection string. That is, ensure there is a port in the string.
+ * @param connection_string The connection string to normalize.
+ * @param default_port The port to use if none is given.
+ * @return The normalized connection string.
+ */
+std::string NormalizeConnectionString(const std::string &connection_string, uint16 default_port)
+{
+	uint16 port = default_port;
+	std::string_view ip = ParseFullConnectionString(connection_string, port);
+	return std::string(ip) + ":" + std::to_string(port);
+}
+
+/**
  * Convert a string containing either "hostname" or "hostname:ip" to a
  * NetworkAddress.
  *
@@ -1131,23 +1144,27 @@ static void NetworkGenerateServerId()
 	seprintf(_settings_client.network.network_id, lastof(_settings_client.network.network_id), "%s", hex_output);
 }
 
-void NetworkStartDebugLog(const std::string &connection_string)
-{
-	extern SOCKET _debug_socket;  // Comes from debug.c
+class TCPNetworkDebugConnecter : TCPConnecter {
+public:
+	TCPNetworkDebugConnecter(const std::string &connection_string) : TCPConnecter(connection_string, NETWORK_DEFAULT_DEBUGLOG_PORT) {}
 
-	NetworkAddress address = ParseConnectionString(connection_string, NETWORK_DEFAULT_DEBUGLOG_PORT);
+	void OnFailure() override
+	{
+		DEBUG(net, 0, "Failed to open connection to %s for redirecting DEBUG()", this->connection_string.c_str());
+	}
 
-	DEBUG(net, 0, "Redirecting DEBUG() to %s", address.GetAddressAsString().c_str());
+	void OnConnect(SOCKET s) override
+	{
+		DEBUG(net, 0, "Redirecting DEBUG() to %s", this->connection_string.c_str());
 
-	SOCKET s = address.Connect();
-	if (s == INVALID_SOCKET) {
-		DEBUG(net, 0, "Failed to open socket for redirection DEBUG()");
-		return;
+		extern SOCKET _debug_socket;
+		_debug_socket = s;
 	}
+};
 
-	_debug_socket = s;
-
-	DEBUG(net, 0, "DEBUG() is now redirected");
+void NetworkStartDebugLog(const std::string &connection_string)
+{
+	new TCPNetworkDebugConnecter(connection_string);
 }
 
 /** This tries to launch the network for a given OS */