SearchAndReplaceInputStream.java

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

/**
 * @author alex.collins
 */
public class SearchAndReplaceInputStream extends InputStream {
    private final InputStream is;
    private final byte[] search;
    private final byte[] replace;

    private int len, pos, idx;
    private byte ch, buf[];

    public SearchAndReplaceInputStream(InputStream is, byte[] search, byte[] replace) {
        this.is = is;
        this.search = search;
        this.replace = replace;

        len = this.search.length;
        pos = 0;
        idx = -1;

        ch = this.search[0];
        buf = new byte[Math.max(this.search.length, this.replace.length)];
    }

    @Override
    public int read() throws IOException {
        if (idx == -1) {
            idx = 0;

            int i;
            while ((i = is.read()) != -1 && (buf[pos] = (byte) i) == ch) {
                if (++pos == len) {
                    break;
                }

                ch = search[pos];
            }

            if (pos == len) {
                buf = new byte[Math.max(this.search.length, this.replace.length)];
                System.arraycopy(replace, 0, buf, 0, replace.length);
            }

            pos = 0;
            ch = search[pos];
        }

        int toReturn = -1;
        if (idx > -1 && buf[idx] != 0) {
            toReturn = buf[idx];
            buf[idx] = 0;
            if (idx < buf.length - 1 && buf[idx + 1] != 0) {
                idx++;
            } else {
                idx = -1;
                buf = new byte[Math.max(this.search.length, this.replace.length)];
            }
        }

        return toReturn;
    }
}