server/protocols/jmap-rfc-8621/src/main/java/org/apache/james/jmap/mailet/TextCalendarBodyToAttachment.java

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package org.apache.james.jmap.mailet;

import java.util.Collections;
import java.util.List;

import jakarta.mail.Header;
import jakarta.mail.MessagingException;
import jakarta.mail.Multipart;
import jakarta.mail.Part;
import jakarta.mail.internet.MimeBodyPart;
import jakarta.mail.internet.MimeMessage;
import jakarta.mail.internet.MimeMultipart;

import org.apache.mailet.Mail;
import org.apache.mailet.base.GenericMailet;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableList;

/**
 * This mailet converts Content-Type of MimeMessage from text/calendar to mulitpart/mixed
 *
 * The BodyPart should be retrieved from content of text/calendar with all the same "Content-*" headers from original message
 * and those "Content-" header are removed from original message
 *
 * <br />
 * It does not takes any parameter
 *
 * Sample configuration:
 * <p/>
 * <pre><code>
 * &lt;mailet match="All" class="TextCalendarBodyToAttachment"/&gt;
 * </code></pre>
 *
 */
public class TextCalendarBodyToAttachment extends GenericMailet {
    private static final String TEXT_CALENDAR_TYPE = "text/calendar";
    private static final String CONTENT_HEADER_PREFIX = "Content-";

    @Override
    public String getMailetInfo() {
        return "Moves body part of content type text/calendar to attachment";
    }

    @Override
    public void service(Mail mail) throws MessagingException {
        MimeMessage mimeMessage = mail.getMessage();
        if (mimeMessage.isMimeType(TEXT_CALENDAR_TYPE)) {
            processTextBodyAsAttachment(mimeMessage);
        }
    }

    @VisibleForTesting
    void processTextBodyAsAttachment(MimeMessage mimeMessage) throws MessagingException {
        List<Header> contentHeaders = getContentHeadersFromMimeMessage(mimeMessage);

        removeAllContentHeaderFromMimeMessage(mimeMessage, contentHeaders);

        Multipart multipart = new MimeMultipart();
        multipart.addBodyPart(createMimeBodyPartWithContentHeadersFromMimeMessage(mimeMessage, contentHeaders));

        mimeMessage.setContent(multipart);
        mimeMessage.saveChanges();
    }

    private List<Header> getContentHeadersFromMimeMessage(MimeMessage mimeMessage) throws MessagingException {
        return Collections.list(mimeMessage.getAllHeaders())
            .stream()
            .filter(header -> header.getName().startsWith(CONTENT_HEADER_PREFIX))
            .collect(ImmutableList.toImmutableList());
    }

    private MimeBodyPart createMimeBodyPartWithContentHeadersFromMimeMessage(MimeMessage mimeMessage, List<Header> contentHeaders) throws MessagingException {
        MimeBodyPart fileBody = new MimeBodyPart(mimeMessage.getRawInputStream());
        for (Header header : contentHeaders) {
            fileBody.setHeader(header.getName(), header.getValue());
        }

        fileBody.setDisposition(Part.ATTACHMENT);
        return fileBody;
    }

    private void removeAllContentHeaderFromMimeMessage(MimeMessage mimeMessage, List<Header> contentHeaders) throws MessagingException {
        for (Header header : contentHeaders) {
            mimeMessage.removeHeader(header.getName());
        }
    }
}