/*******************************************************************************
 *
 * Copyright (c) 2004-2009 Oracle Corporation.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 * 
 *    Kohsuke Kawaguchi
 *
 *
 *******************************************************************************/ 

package hudson.util;

import org.apache.commons.io.output.ByteArrayOutputStream;

import java.io.FilterInputStream;
import java.io.InputStream;
import java.io.IOException;

/**
 * {@link FilterInputStream} that buffers the first N bytes to a byte array on
 * the side. This byte array can be then accessed later.
 *
 * <p> Useful for sniffing the content of the stream after the error is
 * discovered.
 *
 * @author Kohsuke Kawaguchi
 */
public class HeadBufferingStream extends FilterInputStream {

    private final ByteArrayOutputStream side;
    private final int sideBufferSize;

    public HeadBufferingStream(InputStream in, int sideBufferSize) {
        super(in);
        this.sideBufferSize = sideBufferSize;
        this.side = new ByteArrayOutputStream(sideBufferSize);
    }

    @Override
    public int read() throws IOException {
        int i = in.read();
        if (i >= 0 && space() > 0) {
            side.write(i);
        }
        return i;
    }

    @Override
    public int read(byte b[], int off, int len) throws IOException {
        int r = in.read(b, off, len);
        if (r > 0) {
            int sp = space();
            if (sp > 0) {
                side.write(b, off, Math.min(r, sp));
            }
        }
        return r;
    }

    /**
     * Available space in the {@link #side} buffer.
     */
    private int space() {
        return sideBufferSize - side.size();
    }

    /**
     * Read until we fill up the side buffer.
     */
    public void fillSide() throws IOException {
        byte[] buf = new byte[space()];
        while (space() > 0) {
            if (read(buf) < 0) {
                return;
            }
        }
    }

    /**
     * Gets the side buffer content.
     */
    public byte[] getSideBuffer() {
        return side.toByteArray();
    }
}