Feature: allow setting (game) coordinator and content server connection strings using environment variables

OTTD_COORDINATOR_CS for the game coordinator defaults to coordinator.openttd.org:3976
OTTD_CONTENT_SERVER_CS for the content server defaults to content.openttd.org:3978
OTTD_CONTENT_MIRROR_CS for the content mirror server defaults to binaries.openttd.org:80

5 files changed, 67 insertions, 9 deletions

diff --git a/src/network/core/CMakeLists.txt b/src/network/core/CMakeLists.txt
index 6eb255f6f..82bf7843d 100644
--- a/src/network/core/CMakeLists.txt
+++ b/src/network/core/CMakeLists.txt
@@ -1,6 +1,7 @@
 add_files(
     address.cpp
     address.h
+    config.cpp
     config.h
     core.cpp
     core.h
diff --git a/src/network/core/config.cpp b/src/network/core/config.cpp
new file mode 100644
index 000000000..c5fe3adbd
--- /dev/null
+++ b/src/network/core/config.cpp
@@ -0,0 +1,59 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @file config.cpp Configuration of the connection strings for network stuff using environment variables.
+ */
+
+#include "../../stdafx.h"
+
+#include <cstdlib>
+#include "../../string_func.h"
+
+#include "../../safeguards.h"
+
+/**
+ * Get the environment variable using std::getenv and when it is an empty string (or nullptr), return a fallback value instead.
+ * @param variable The environment variable to read from.
+ * @param fallback The fallback in case the environment variable is not set.
+ * @return The environment value, or when that does not exist the given fallback value.
+ */
+static const char *GetEnv(const char *variable, const char *fallback)
+{
+	const char *value = std::getenv(variable);
+	return StrEmpty(value) ? fallback : value;
+}
+
+/**
+ * Get the connection string for the game coordinator from the environment variable OTTD_COORDINATOR_CS,
+ * or when it has not been set a hard coded default DNS hostname of the production server.
+ * @return The game coordinator's connection string.
+ */
+const char *NetworkCoordinatorConnectionString()
+{
+	return GetEnv("OTTD_COORDINATOR_CS", "coordinator.openttd.org");
+}
+
+/**
+ * Get the connection string for the content server from the environment variable OTTD_CONTENT_SERVER_CS,
+ * or when it has not been set a hard coded default DNS hostname of the production server.
+ * @return The game coordinator's connection string.
+ */
+const char *NetworkContentServerConnectionString()
+{
+	return GetEnv("OTTD_CONTENT_SERVER_CS", "content.openttd.org");
+}
+
+/**
+ * Get the connection string for the content mirror from the environment variable OTTD_CONTENT_MIRROR_CS,
+ * or when it has not been set a hard coded default DNS hostname of the production server.
+ * @return The game coordinator's connection string.
+ */
+const char *NetworkContentMirrorConnectionString()
+{
+	return GetEnv("OTTD_CONTENT_MIRROR_CS", "binaries.openttd.org");
+}
diff --git a/src/network/core/config.h b/src/network/core/config.h
index ab1c3082e..d64dec2d9 100644
--- a/src/network/core/config.h
+++ b/src/network/core/config.h
@@ -12,12 +12,10 @@
 #ifndef NETWORK_CORE_CONFIG_H
 #define NETWORK_CORE_CONFIG_H
 
-/** DNS hostname of the Game Coordinator server */
-static const char * const NETWORK_COORDINATOR_SERVER_HOST       = "coordinator.openttd.org";
-/** DNS hostname of the content server */
-static const char * const NETWORK_CONTENT_SERVER_HOST           = "content.openttd.org";
-/** DNS hostname of the HTTP-content mirror server */
-static const char * const NETWORK_CONTENT_MIRROR_HOST           = "binaries.openttd.org";
+const char *NetworkCoordinatorConnectionString();
+const char *NetworkContentServerConnectionString();
+const char *NetworkContentMirrorConnectionString();
+
 /** URL of the HTTP mirror system */
 static const char * const NETWORK_CONTENT_MIRROR_URL            = "/bananas";
 
diff --git a/src/network/network_content.cpp b/src/network/network_content.cpp
index eff54885d..13172f9ea 100644
--- a/src/network/network_content.cpp
+++ b/src/network/network_content.cpp
@@ -342,7 +342,7 @@ void ClientNetworkContentSocketHandler::DownloadSelectedContentHTTP(const Conten
 
 	this->http_response_index = -1;
 
-	new NetworkHTTPContentConnecter(NETWORK_CONTENT_MIRROR_HOST, this, NETWORK_CONTENT_MIRROR_URL, content_request);
+	new NetworkHTTPContentConnecter(NetworkContentMirrorConnectionString(), this, NETWORK_CONTENT_MIRROR_URL, content_request);
 	/* NetworkHTTPContentConnecter takes over freeing of content_request! */
 }
 
@@ -774,7 +774,7 @@ void ClientNetworkContentSocketHandler::Connect()
 {
 	if (this->sock != INVALID_SOCKET || this->isConnecting) return;
 	this->isConnecting = true;
-	new NetworkContentConnecter(NETWORK_CONTENT_SERVER_HOST);
+	new NetworkContentConnecter(NetworkContentServerConnectionString());
 }
 
 /**
diff --git a/src/network/network_coordinator.cpp b/src/network/network_coordinator.cpp
index b9299d549..5f1f9f9d1 100644
--- a/src/network/network_coordinator.cpp
+++ b/src/network/network_coordinator.cpp
@@ -159,7 +159,7 @@ void ClientNetworkCoordinatorSocketHandler::Connect()
 	this->connecting = true;
 	this->last_activity = std::chrono::steady_clock::now();
 
-	new NetworkCoordinatorConnecter(NETWORK_COORDINATOR_SERVER_HOST);
+	new NetworkCoordinatorConnecter(NetworkCoordinatorConnectionString());
 }
 
 NetworkRecvStatus ClientNetworkCoordinatorSocketHandler::CloseConnection(bool error)