core/src/main/java/org/apache/james/mime4j/io/LimitedInputStream.java

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 * Licensed to the Apache Software Foundation (ASF) under one   *
 * or more contributor license agreements.  See the NOTICE file *
 * distributed with this work for additional information        *
 * regarding copyright ownership.  The ASF licenses this file   *
 * to you 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   *
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 *   http://www.apache.org/licenses/LICENSE-2.0                 *
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 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY       *
 * KIND, either express or implied.  See the License for the    *
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 * under the License.                                           *
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package org.apache.james.mime4j.io;

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

public class LimitedInputStream extends PositionInputStream {

    private final long limit;

    public LimitedInputStream(InputStream instream, long limit) {
        super(instream);
        if (limit < 0) {
            throw new IllegalArgumentException("Limit may not be negative");
        }
        this.limit = limit;
    }

    private void enforceLimit() throws IOException {
        if (position >= limit) {
            throw new IOException("Input stream limit exceeded. Limit was " + limit + " and position " + position);
        }
    }

    @Override
    public int read() throws IOException {
        enforceLimit();
        return super.read();
    }

    @Override
    public int read(byte b[], int off, int len) throws IOException {
        enforceLimit();
        len = Math.min(len, getBytesLeft());
        return super.read(b, off, len);
    }

    @Override
    public long skip(long n) throws IOException {
        enforceLimit();
        n = Math.min(n, getBytesLeft());
        return super.skip(n);
    }

    private int getBytesLeft() {
        return (int)Math.min(Integer.MAX_VALUE, limit - position);
    }

}