Major plugin refactor and cleanup.

Switched to POCO library for unified platform/library interface.
Deprecated the external module API. It was creating more problems than solving.
Removed most built-in libraries in favor of system libraries for easier maintenance.
Cleaned and secured code with help from static analyzers.

vendor/POCO/Foundation/include/Poco/Base64Decoder.h

@@ -0,0 +1,110 @@
+//
+// Base64Decoder.h
+//
+// Library: Foundation
+// Package: Streams
+// Module:  Base64
+//
+// Definition of class Base64Decoder.
+//
+// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
+// and Contributors.
+//
+// SPDX-License-Identifier:	BSL-1.0
+//
+
+
+#ifndef Foundation_Base64Decoder_INCLUDED
+#define Foundation_Base64Decoder_INCLUDED
+
+
+#include "Poco/Foundation.h"
+#include "Poco/UnbufferedStreamBuf.h"
+#include <istream>
+
+
+namespace Poco {
+
+
+class Foundation_API Base64DecoderBuf: public UnbufferedStreamBuf
+	/// This streambuf base64-decodes all data read
+	/// from the istream connected to it.
+	///
+	/// Note: For performance reasons, the characters 
+	/// are read directly from the given istream's 
+	/// underlying streambuf, so the state
+	/// of the istream will not reflect that of
+	/// its streambuf.
+{
+public:
+	Base64DecoderBuf(std::istream& istr, int options = 0);
+	~Base64DecoderBuf();
+
+private:
+	int readFromDevice();
+	int readOne();
+
+	int             _options;
+	unsigned char   _group[3];
+	int             _groupLength;
+	int             _groupIndex;
+	std::streambuf& _buf;
+	const unsigned char* _pInEncoding;
+
+	static unsigned char IN_ENCODING[256];
+	static bool          IN_ENCODING_INIT;
+	static unsigned char IN_ENCODING_URL[256];
+	static bool          IN_ENCODING_URL_INIT;
+
+private:
+	Base64DecoderBuf(const Base64DecoderBuf&);
+	Base64DecoderBuf& operator = (const Base64DecoderBuf&);
+};
+
+
+class Foundation_API Base64DecoderIOS: public virtual std::ios
+	/// The base class for Base64Decoder.
+	///
+	/// This class is needed to ensure the correct initialization
+	/// order of the stream buffer and base classes.
+{
+public:
+	Base64DecoderIOS(std::istream& istr, int options = 0);
+	~Base64DecoderIOS();
+	Base64DecoderBuf* rdbuf();
+
+protected:
+	Base64DecoderBuf _buf;
+
+private:
+	Base64DecoderIOS(const Base64DecoderIOS&);
+	Base64DecoderIOS& operator = (const Base64DecoderIOS&);
+};
+
+
+class Foundation_API Base64Decoder: public Base64DecoderIOS, public std::istream
+	/// This istream base64-decodes all data
+	/// read from the istream connected to it.
+	///
+	/// The class implements RFC 4648 - https://tools.ietf.org/html/rfc4648
+	///
+	/// Note: For performance reasons, the characters 
+	/// are read directly from the given istream's 
+	/// underlying streambuf, so the state
+	/// of the istream will not reflect that of
+	/// its streambuf.
+{
+public:
+	Base64Decoder(std::istream& istr, int options = 0);
+	~Base64Decoder();
+
+private:
+	Base64Decoder(const Base64Decoder&);
+	Base64Decoder& operator = (const Base64Decoder&);
+};
+
+
+} // namespace Poco
+
+
+#endif // Foundation_Base64Decoder_INCLUDED