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The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. 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.

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package org.bouncycastle.mime.encoding;

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

/**
 * Input stream that processes quoted-printable data, converting it into what was originally intended.
 */
public class QuotedPrintableInputStream
    extends FilterInputStream
{

    public QuotedPrintableInputStream(InputStream input)
    {
        super(input);
    }

    public int read(byte[] buf, int bufOff, int len) throws IOException
    {
        int i = 0;
        while (i != len)
        {
            int ch = this.read();
            if (ch < 0)
            {
                break;
            }
            buf[i + bufOff] = (byte)ch;
            i++;
        }

        if (i == 0)
        {
            return -1;
        }
        
        return i;
    }

    public int read()
        throws IOException
    {
        int v = in.read();
        if (v == -1)
        {
            return -1;
        }
 
        // V was the quote '=' character/
        while (v == '=')
        {
            //
            // Get the next character.
            //
            int j = in.read();
            if (j == -1)
            {
                throw new IllegalStateException("Quoted '=' at end of stream");
            }

            // For systems generating CRLF line endings.
            if (j == '\r')
            {
                j = in.read();
                if (j == '\n')
                {
                    //
                    // This was a line break that was not actually a line break in the original information.
                    // So return the next data.
                    //
                    j = in.read();
                }
                v = j;
                continue;
            }
            else if (j == '\n')
            {
                // As above but without preceding CR.
                v = in.read();
                continue;
            }
            else
            {

                int chr = 0;

                if (j >= '0' && j <= '9')
                {
                    chr = j - '0';
                }
                else if (j >= 'A' && j <= 'F')
                {
                    chr = 10 + (j - 'A');
                }
                else
                {
                    throw new IllegalStateException("Expecting '0123456789ABCDEF after quote that was not immediately followed by LF or CRLF");
                }

                chr <<= 4;

                j = in.read();

                if (j >= '0' && j <= '9')
                {
                    chr |= j - '0';
                }
                else if (j >= 'A' && j <= 'F')
                {
                    chr |= 10 + (j - 'A');
                }
                else
                {
                    throw new IllegalStateException("Expecting second '0123456789ABCDEF after quote that was not immediately followed by LF or CRLF");
                }

                return chr;
            }
        }

        return v;
    }
}