ErrorOutputStream.java

// Copyright 2014 Michel Kraemer
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package de.undercouch.citeproc.tool.shell;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * A filter output stream that colors everything in red on ANSI terminals
 * @author Michel Kraemer
 */
public class ErrorOutputStream extends FilterOutputStream {
	/**
	 * True if we're currently writing to the underlying output stream
	 */
	private boolean writing = false;
	
	/**
	 * Constructs a new filter output stream
	 * @param out the underlying output stream
	 */
	public ErrorOutputStream(OutputStream out) {
		super(out);
	}
	
	@Override
	public void write(int b) throws IOException {
		boolean oldwriting = enableRed();
		super.write(b);
		if (!oldwriting) {
			disableRed();
		}
	}
	
	@Override
	public void write(byte b[], int off, int len) throws IOException {
		boolean oldwriting = enableRed();
		super.write(b, off, len);
		if (!oldwriting) {
			disableRed();
		}
	}
	
	/**
	 * Enables colored output
	 * @return true if the colored output was already enabled before
	 * @throws IOException if writing to the underlying output stream failed
	 */
	private boolean enableRed() throws IOException {
		boolean oldwriting = writing;
		if (!writing) {
			writing = true;
			byte[] en = "\u001B[31m".getBytes();
			super.write(en, 0, en.length);
		}
		return oldwriting;
	}
	
	/**
	 * Disabled colored output
	 * @throws IOException if writing to the underlying output stream failed
	 */
	private void disableRed() throws IOException {
		byte[] dis = "\u001B[0m".getBytes();
		super.write(dis, 0, dis.length);
		writing = false;
	}
}