Untested java.io.Reader decorator that filters out a set of characters

CharacterSkippingReader.java

/*******************************************************************************
 * Copyright (c) 2025 Xored Software Inc and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-v20.html
 *
 * Contributors:
 *     Xored Software Inc - initial API and implementation and/or initial documentation
 *******************************************************************************/
package org.eclipse.rcptt.core.persistence.plain;

import java.io.FilterReader;
import java.io.IOException;
import java.io.Reader;
import java.nio.CharBuffer;
import java.util.Objects;

public class CharacterSkippingReader extends FilterReader {
	private final CharBuffer buffer = CharBuffer.allocate(2048);
	private String charsToRemove;

	public CharacterSkippingReader(Reader in, String charsToRemove) {
		super(in);
		this.charsToRemove = Objects.requireNonNull(charsToRemove);
	}


	@Override
	public int read(char[] cbuf, int off, int len) throws IOException {
		int toRead = Math.min(buffer.remaining(), len);
		buffer.get(cbuf, off, toRead);
		if (toRead > 0) {
			return toRead;
		}
		int result = readUpstream();
		if (result <= 0) {
			return result;
		}
		toRead = Math.min(buffer.remaining(), len);
		buffer.get(cbuf, off, toRead);
		return toRead;
	}
	
	@Override
	public int read(CharBuffer target) throws IOException {
		int result = buffer.read(target);
		if (result > 0) {
			return result;
		}
		result = readUpstream();
		if (result <= 0) {
			return result;
		}
		return buffer.read(target);
	}
	
	@Override
	public void reset() throws IOException {
		super.reset();
		buffer.clear();
	}

	private int readUpstream() throws IOException {
		buffer.compact();
		try {
			int startPosition = buffer.position();
			while (buffer.position() == startPosition) {
				int result = in.read(buffer);
				assert buffer.position() >= startPosition;
				if (result <= 0) {
					return result;
				}
				removeChars(buffer, charsToRemove);
				assert buffer.position() >= startPosition;
			}
			return buffer.position() - startPosition;
		} finally {
			buffer.flip();
		}
	}
	
	private static void removeChars(CharBuffer inout, String charsToRemove) {
		int readCursor = 0, writeCursor = 0;
		for (;;) {
			assert readCursor >= writeCursor;
			if (readCursor >= inout.position()) {
				break;
			}
			char c = inout.get(readCursor++);
			if (charsToRemove.indexOf(c) >= 0) {
				continue;
			}
			inout.put(writeCursor++, c);
		}
		inout.position(writeCursor);
	}
}