--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/lib/BackspaceUnescapingProcessor.h	Sat Nov 28 18:14:15 2020 +0100
@@ -0,0 +1,70 @@
+/**
+ * Relational pipes
+ * Copyright © 2020 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 <sstream>
+
+#include "UnescapingProcessor.h"
+
+using namespace std;
+using namespace relpipe::writer;
+
+namespace relpipe {
+namespace in {
+namespace ini {
+namespace lib {
+
+class BackspaceUnescapingProcessor : public UnescapingProcessor {
+private:
+	const bool lastEscaphingPhase = true;
+public:
+
+	std::string unescape(const std::string& s, const TextType type) override {
+		std::stringstream result;
+		for (int i = 0, length = s.size(); i < length; i++) {
+			char ch = s[i];
+			if (i + 1 < length && ch == ESC) {
+				ch = s[i + 1];
+				if (ch == ESC) put(result, ESC, i); // unescape \\ to \.
+				else if (lastEscaphingPhase) throw std::logic_error(std::string("Unsupported escape sequence: ") + ch);
+				else result.put(ESC); // keep the escape sequence for later unescaping phase
+			} else if (ch == ESC) {
+				throw std::logic_error(std::string("Missing escape sequence")); // this should not happen
+			} else {
+				result.put(ch);
+			}
+		}
+		return result.str();
+	}
+
+	/**
+	 * @param lastEscaphingPhase whether this is final unescaping stage.
+	 * By default it is set to true, thus no unrecognized escape sequences may left after this stage.
+	 * Setting this to false is dangerous and may lead to errors and ambiguous behavior.
+	 * It should be used only as a last resort.
+	 * Because both "\\ \xxx" and "\ \xxx" will be converted to "\ \xxx" and the information will be lost.
+	 * So, it is usually better to keep the "\" escaped as "\\" and process both the escaped backspaces and unrecognized escape sequences later.
+	 */
+	BackspaceUnescapingProcessor(bool lastEscaphingPhase = true) : lastEscaphingPhase(lastEscaphingPhase) {
+	}
+
+};
+
+}
+}
+}
+}