Implement NetworkManager

For now there are two methods:

- `NETWORK:IsUrlAllowed()`: Check whether access to a certain URL is allowed.
- `NETWORK:HttpRequest()`: Perform an HTTP request.

By default access to the network is disabled for all target hosts. It
can be enabled by setting `HttpEnable=1` in the preferences. Individual
hosts have to be added to `HttpAllowHosts` as a comma separated list to
allow access.

See included docs for more details on usage.

src/NetworkManager.h

@@ -0,0 +1,105 @@
+#ifndef NETWORK_MANAGER_H
+#define NETWORK_MANAGER_H
+
+#include "Preference.h"
+#include "StdString.h"
+
+#include <functional>
+#include <map>
+#include <string>
+
+#include <ixwebsocket/IXHttp.h>
+#include <ixwebsocket/IXHttpClient.h>
+
+#include "EnumHelper.h"
+#include "LuaManager.h"
+
+struct lua_State;
+
+enum HttpErrorCode
+{
+	HttpErrorCode_Blocked,
+	HttpErrorCode_UnknownError,
+
+	// from IXWebSocket
+	HttpErrorCode_CannotConnect,
+	HttpErrorCode_Timeout,
+	HttpErrorCode_Gzip,
+	HttpErrorCode_UrlMalformed,
+	HttpErrorCode_CannotCreateSocket,
+	HttpErrorCode_SendError,
+	HttpErrorCode_ReadError,
+	HttpErrorCode_CannotReadStatusLine,
+	HttpErrorCode_MissingStatus,
+	HttpErrorCode_HeaderParsingError,
+	HttpErrorCode_MissingLocation,
+	HttpErrorCode_TooManyRedirects,
+	HttpErrorCode_ChunkReadError,
+	HttpErrorCode_CannotReadBody,
+
+	NUM_HttpErrorCode,
+	HttpErrorCode_Invalid,
+};
+const RString& HttpErrorCodeToString(HttpErrorCode dc);
+HttpErrorCode StringToHttpErrorCode(const RString& sDC);
+LuaDeclareType( HttpErrorCode );
+
+struct HttpRequestArgs
+{
+	std::string url;
+	std::string method = ix::HttpClient::kGet;
+	std::string body;
+	std::string multipartBoundary;
+	std::map<string, string> headers;
+	int connectTimeout = -1;
+	int transferTimeout = -1;
+	std::function<void(const ix::HttpResponsePtr& response)> onResponse = [](const ix::HttpResponsePtr& response) {};
+};
+
+class NetworkManager
+{
+public:
+	NetworkManager();
+	~NetworkManager();
+
+	bool IsUrlAllowed(const std::string& url);
+	void HttpRequest(const HttpRequestArgs& args);
+
+	// Lua
+	void PushSelf(lua_State *L);
+
+private:
+	ix::HttpClient httpClient;
+
+	static Preference<bool> httpEnabled;
+	static Preference<RString> httpAllowHosts;
+};
+
+extern NetworkManager*	NETWORK;
+
+#endif
+
+/*
+ * (c) 2021 Martin Natano
+ * All rights reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, and/or sell copies of the Software, and to permit persons to
+ * whom the Software is furnished to do so, provided that the above
+ * copyright notice(s) and this permission notice appear in all copies of
+ * the Software and that both the above copyright notice(s) and this
+ * permission notice appear in supporting documentation.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF
+ * THIRD PARTY RIGHTS. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR HOLDERS
+ * INCLUDED IN THIS NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT
+ * OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+ * OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */