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Simple API, Complex Emails. Now with DKIM support
There is a newer version: 8.12.2
/*
 * Copyright © 2009 Benny Bottema ([email protected])
 *
 * Licensed 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
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.simplejavamail.internal.dkimsupport;

import jakarta.mail.MessagingException;
import jakarta.mail.internet.MimeMessage;
import org.jetbrains.annotations.NotNull;
import org.simplejavamail.api.email.Email;
import org.simplejavamail.api.email.Recipient;
import org.simplejavamail.api.email.config.DkimConfig;
import org.simplejavamail.internal.modules.DKIMModule;
import org.simplejavamail.utils.mail.dkim.Canonicalization;
import org.simplejavamail.utils.mail.dkim.DkimSigner;
import org.simplejavamail.utils.mail.dkim.SigningAlgorithm;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;
import java.util.Collections;

import static org.simplejavamail.internal.util.MiscUtil.defaultTo;
import static org.simplejavamail.utils.mail.dkim.Canonicalization.RELAXED;
import static org.simplejavamail.utils.mail.dkim.Canonicalization.SIMPLE;
import static org.simplejavamail.utils.mail.dkim.SigningAlgorithm.SHA256_WITH_RSA;

/**
 * This class only serves to hide the DKIM implementation behind an easy-to-load-with-reflection class.
 */
@SuppressWarnings("unused") // it is ued through reflection
public class DKIMSigner implements DKIMModule {

	private static final Logger LOGGER = LoggerFactory.getLogger(DKIMSigner.class);

	/**
	 * @see DKIMModule#signMessageWithDKIM(Email email, MimeMessage, DkimConfig, Recipient)
	 */
	public MimeMessage signMessageWithDKIM(@NotNull Email email, @NotNull final MimeMessage messageToSign, @NotNull final DkimConfig dkimConfig, @NotNull final Recipient fromRecipient) {
		LOGGER.debug("signing MimeMessage with DKIM...");
		try {
			final DkimSigner dkimSigner = new DkimSigner(dkimConfig.getDkimSigningDomain(), dkimConfig.getDkimSelector(), new ByteArrayInputStream(dkimConfig.getDkimPrivateKeyData()));

			defaultTo(dkimConfig.getExcludedHeadersFromDkimDefaultSigningList(), Collections.emptySet())
					.forEach(dkimSigner::removeHeaderToSign);
			dkimSigner.setIdentity(fromRecipient.getAddress());
			dkimSigner.setHeaderCanonicalization(mapToNativeCanonicalization(defaultTo(dkimConfig.getHeaderCanonicalization(), DkimConfig.Canonicalization.RELAXED)));
			dkimSigner.setBodyCanonicalization(mapToNativeCanonicalization(defaultTo(dkimConfig.getBodyCanonicalization(), DkimConfig.Canonicalization.RELAXED)));
			dkimSigner.setSigningAlgorithm(SigningAlgorithm.valueOf(defaultTo(dkimConfig.getSigningAlgorithm(), SHA256_WITH_RSA.name())));
			dkimSigner.setLengthParam(defaultTo(dkimConfig.getUseLengthParam(), false));
			dkimSigner.setZParam(false);

			// during our junit tests, we don't want to actually connect to the internet to check the domain key
			if (fromRecipient.getAddress().endsWith("supersecret-testing-domain.com")) {
				dkimSigner.setCheckDomainKey(false);
			}

			return new DkimMessageIdFixingMimeMessage(messageToSign, dkimSigner, email.getId());
		} catch (IOException | NoSuchAlgorithmException | InvalidKeySpecException | MessagingException e) {
			throw new org.simplejavamail.internal.dkimsupport.DKIMSigningException(org.simplejavamail.internal.dkimsupport.DKIMSigningException.ERROR_SIGNING_DKIM_INVALID_DOMAINKEY, e);
		}
	}

	private static Canonicalization mapToNativeCanonicalization(DkimConfig.Canonicalization canonicalization) {
		return canonicalization == DkimConfig.Canonicalization.SIMPLE ? SIMPLE : RELAXED;
	}

	@Override
	public boolean isMessageIdFixingMessage(MimeMessage message) {
		return message instanceof DkimMessageIdFixingMimeMessage;
	}
}