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The Bouncy Castle Java APIs for the OpenPGP Protocol. The APIs are designed primarily to be used in conjunction with the BC FIPS provider. The APIs may also be used with other providers although if being used in a FIPS context it is the responsibility of the user to ensure that any other providers used are FIPS certified and used appropriately.

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package org.bouncycastle.bcpg;

import java.io.ByteArrayInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.channels.FileChannel;

class StreamUtil
{
    private static final long  MAX_MEMORY = Runtime.getRuntime().maxMemory();

    /**
     * Find out possible longest length, capped by available memory.
     *
     * @param in input stream of interest
     * @return length calculation or MAX_VALUE.
     */
    static int findLimit(InputStream in)
    {
        // TODO: this can obviously be improved.
        if (in instanceof ByteArrayInputStream)
        {
            return ((ByteArrayInputStream)in).available();
        }
        else if (in instanceof FileInputStream)
        {
            try
            {
                FileChannel channel = ((FileInputStream)in).getChannel();
                long  size = (channel != null) ? channel.size() : Integer.MAX_VALUE;

                if (size < Integer.MAX_VALUE)
                {
                    return (int)size;
                }
            }
            catch (IOException e)
            {
                // ignore - they'll find out soon enough!
            }
        }

        if (MAX_MEMORY > Integer.MAX_VALUE)
        {
            return Integer.MAX_VALUE;
        }

        return (int)MAX_MEMORY;
    }
}