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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.smime;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Map;

import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.mime.CanonicalOutputStream;
import org.bouncycastle.mime.Headers;
import org.bouncycastle.mime.MimeContext;
import org.bouncycastle.mime.MimeMultipartContext;
import org.bouncycastle.mime.MimeParserContext;
import org.bouncycastle.operator.DigestCalculator;
import org.bouncycastle.operator.OperatorCreationException;
import org.bouncycastle.util.io.TeeInputStream;
import org.bouncycastle.util.io.TeeOutputStream;

public class SMimeMultipartContext
    implements MimeMultipartContext
{
    private final SMimeParserContext parserContext;

    private DigestCalculator[] calculators;


    public SMimeMultipartContext(MimeParserContext parserContext, Headers headers)
    {
        this.parserContext = (SMimeParserContext)parserContext;
        this.calculators = createDigestCalculators(headers);
    }

    DigestCalculator[] getDigestCalculators()
    {
        return calculators;
    }

    OutputStream getDigestOutputStream()
    {
        if (calculators.length == 1)
        {
            return calculators[0].getOutputStream();
        }
        else
        {
            OutputStream compoundStream = calculators[0].getOutputStream();

            for (int i = 1; i < calculators.length; i++)
            {
                compoundStream = new TeeOutputStream(calculators[i].getOutputStream(), compoundStream);
            }

            return compoundStream;
        }
    }

    private DigestCalculator[] createDigestCalculators(Headers headers)
    {
        try
        {
            Map contentTypeFields = headers.getContentTypeAttributes();

            String micalgs = (String)contentTypeFields.get("micalg");
            if (micalgs == null)
            {
                throw new IllegalStateException("No micalg field on content-type header");
            }

            String[] algs = micalgs.substring(micalgs.indexOf('=') + 1).split(",");
            DigestCalculator[] dcOut = new DigestCalculator[algs.length];

            for (int t = 0; t < algs.length; t++)
            {
                // Deal with possibility of quoted parts, eg  "SHA1","SHA256" etc
                String alg = SMimeUtils.lessQuotes(algs[t]).trim();
                dcOut[t] = parserContext.getDigestCalculatorProvider().get(
                    new AlgorithmIdentifier(SMimeUtils.getDigestOID(alg)));
            }

            return dcOut;
        }
        catch (OperatorCreationException e)
        {
            return null;
        }
    }

    public MimeContext createContext(final int partNo)
        throws IOException
    {
        return new MimeContext()
        {
            public InputStream applyContext(Headers headers, InputStream contentStream)
                throws IOException
            {
                if (partNo == 0)
                {
                    OutputStream digestOut = getDigestOutputStream();

                    headers.dumpHeaders(digestOut);

                    digestOut.write('\r');
                    digestOut.write('\n');

                    return new TeeInputStream(contentStream, new CanonicalOutputStream(parserContext, headers, digestOut));
                }

                return contentStream;
            }
        };
    }

    public InputStream applyContext(Headers headers, InputStream contentStream)
        throws IOException
    {
        return contentStream;
    }
}