diff -r 28294b895e5e -r 68a281aefa76 src/lib/TransactionalBuffer.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/lib/TransactionalBuffer.h	Sat Jul 24 17:35:27 2021 +0200
@@ -0,0 +1,139 @@
+/**
+ * Relational pipes
+ * Copyright © 2021 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 <string>
+#include <exception>
+#include <cstring>
+
+#include "AbstractParser.h"
+
+namespace relpipe {
+namespace in {
+namespace asn1 {
+namespace lib {
+
+class TransactionalBuffer {
+private:
+	uint8_t* buffer;
+	size_t bufferSize;
+	bool hasData = false;
+	size_t writePosition = 0;
+	// size_t writePositionCommited = 0; // TODO: transactions also on the writing side?
+	size_t readPosition = 0;
+	size_t readPositionCommited = 0;
+
+	size_t bytesRead = 0;
+	size_t bytesReadCommited = 0;
+
+	size_t availableForReading() {
+		if (readPosition < writePosition) return writePosition - readPosition;
+		else if (readPosition > writePosition) return bufferSize - readPosition + writePosition;
+		else if (hasData) return bufferSize;
+		else return 0;
+	}
+
+	size_t availableForWriting() {
+		if (readPositionCommited < writePosition) return bufferSize - writePosition + readPositionCommited;
+		else if (readPositionCommited > writePosition) return readPositionCommited - writePosition;
+		else if (hasData) return 0;
+		else return bufferSize;
+	}
+
+public:
+
+	/**
+	 * Is thrown from read() and peak() methods if there are not enough data.
+	 * Interrupts current update() cycle and causes rollback.
+	 */
+	class ReadBufferUnderflowException {
+		// TODO: common super-class for exceptions, hidden implementation
+	};
+
+	/**
+	 * Is thrown from write() method of the buffer when there is not enough space.
+	 * Interrupts whole process.
+	 */
+	class WriteBufferOverflowException {
+	};
+
+	TransactionalBuffer(size_t initialSize = 4096) : bufferSize(initialSize) {
+		// TODO: initial size + resize + hard upper limit
+		buffer = (uint8_t*) malloc(bufferSize);
+	}
+
+	virtual ~TransactionalBuffer() {
+		free(buffer);
+	}
+
+	void write(const uint8_t* inputBuffer, const size_t length) {
+		if (length == 0) return;
+		if (length > availableForWriting()) throw WriteBufferOverflowException(); // TODO: optional resize
+
+		hasData = true;
+
+		const size_t a = std::min(length, bufferSize - writePosition);
+		const size_t b = length - a;
+
+		// TODO: map buffer twice in the memory in order to create a continuous area and avoid the second memcpy()?
+		memcpy(buffer + writePosition, inputBuffer, a);
+		memcpy(buffer, inputBuffer + a, b);
+
+		writePosition = (writePosition + length) % bufferSize;
+	}
+
+	void read(uint8_t* outputBuffer, const size_t length) {
+		if (length == 0) return;
+
+		peek(outputBuffer, length);
+		readPosition = (readPosition + length) % bufferSize;
+		hasData = readPosition != writePosition;
+		bytesRead += length;
+	}
+
+	void peek(uint8_t* outputBuffer, const size_t length) {
+		if (length == 0) return;
+		if (length > availableForReading()) throw ReadBufferUnderflowException();
+
+		const size_t a = std::min(length, bufferSize - readPosition);
+		const size_t b = length - a;
+
+		memcpy(outputBuffer, buffer + readPosition, a);
+		memcpy(outputBuffer + a, buffer, b);
+	}
+
+	void commitRead() {
+		readPositionCommited = readPosition;
+		bytesReadCommited = bytesRead;
+	}
+
+	void rollbackRead() {
+		readPosition = readPositionCommited;
+		bytesRead = bytesReadCommited;
+	}
+
+	size_t getBytesRead() {
+		return bytesRead;
+	}
+
+};
+
+
+}
+}
+}
+}