--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Hex.h	Thu Apr 21 00:57:30 2022 +0200
@@ -0,0 +1,85 @@
+/**
+ * Relational pipes
+ * Copyright © 2022 František Kučera (Frantovo.cz, GlobalCode.info)
+ *
+ * This program 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 3 of the License.
+ *
+ * This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+
+#include <iomanip>
+#include <iostream>
+#include <sstream>
+#include <vector>
+#include <stdexcept>
+
+namespace relpipe {
+namespace tr {
+namespace http {
+
+class Hex {
+private:
+
+	Hex() {
+	}
+
+	static char fromHex(wchar_t ch) {
+		if (L'0' <= ch && ch <= L'9') return ch - L'0';
+		else if (L'a' <= ch && ch <= L'f') return ch - L'a' + 10;
+		else throw std::invalid_argument("Unable to decode hexadeximal string.");
+	}
+
+public:
+
+	static std::stringstream fromHex(const std::wstring& hex) {
+		std::stringstream octets;
+
+		char octet = 0;
+
+		for (size_t i = 0, limit = hex.size(); i < limit; i++) {
+			if (i % 2 == 0) {
+				octet = fromHex(hex[i]) << 4;
+			} else {
+				octet += fromHex(hex[i]);
+				octets.put(octet);
+			}
+		}
+
+		return octets;
+	}
+
+	static std::wstring toHex(const std::string& octets) {
+		std::wstring_convert < codecvt_utf8<wchar_t>> convertor; // TODO: do not create converter each time
+		std::stringstream hex;
+		hex << std::hex << std::setfill('0') << std::hex;
+		for (size_t i = 0, size = octets.size(); i < size; i++) hex << std::setw(2) << (0xff & octets[i]);
+		return convertor.from_bytes(hex.str());
+	}
+
+	static std::wstring toTxt(const std::string& octets, bool* validEncoding = nullptr) {
+		std::wstring_convert < codecvt_utf8<wchar_t>> convertor; // TODO: do not create converter each time
+		try {
+			if (validEncoding) *validEncoding = true;
+			// TODO: use encoding from the HTTP response headers instead of the constant one?
+			return convertor.from_bytes(octets);
+		} catch (...) {
+			if (validEncoding) *validEncoding = false;
+			std::stringstream filtered;
+			for (char ch : octets) filtered << (ch >= ' ' && ch < 127 ? ch : '.');
+			return convertor.from_bytes(filtered.str());
+		}
+	}
+};
+
+}
+}
+}