package com.atlassian.mail;
   
   import org.apache.commons.io.IOUtils;
   import org.apache.commons.lang.StringUtils;
   import org.apache.commons.lang.Validate;
   import org.apache.log4j.Logger;
   
   import java.io.BufferedReader;
   import java.io.ByteArrayOutputStream;
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.FileNotFoundException;
  import java.io.FileOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.Reader;
  import java.io.StringWriter;
  import java.io.UnsupportedEncodingException;
  import java.net.InetAddress;
  import java.net.UnknownHostException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Locale;
  import java.util.StringTokenizer;
  import java.util.zip.ZipEntry;
  import java.util.zip.ZipOutputStream;
  import javax.activation.DataHandler;
  import javax.activation.DataSource;
  import javax.activation.FileDataSource;
  import javax.mail.Address;
  import javax.mail.BodyPart;
  import javax.mail.Message;
  import javax.mail.MessagingException;
  import javax.mail.Multipart;
  import javax.mail.Part;
  import javax.mail.internet.AddressException;
  import javax.mail.internet.InternetAddress;
  import javax.mail.internet.MimeBodyPart;
  import javax.mail.internet.MimeUtility;
  
  // TODO: Doesn't handle charsets/encoding very well. Or, indeed, at all.
  /**
   * This class contains a bunch of static helper methods that make life a bit easier particularly with the processing of
   * Parts.
   */
  public class MailUtils
  {
      private static final String DEFAULT_ENCODING = "ISO-8859-1";
      
      static final int BUFFER_SIZE = 64 * 1024;
      static final String MULTIPART_ALTERNATE_CONTENT_TYPE = "multipart/alternative";
      static final String MULTIPART_RELATED_CONTENT_TYPE = "multipart/related";
      static final String TEXT_CONTENT_TYPE = "text/plain";
      static final String MESSAGE_CONTENT_TYPE = "message/rfc822";
      static final String HTML_CONTENT_TYPE = "text/html";
      static final String CONTENT_TYPE_X_PKCS7 = "application/x-pkcs7-signature";
      static final String CONTENT_TYPE_PKCS7 = "application/pkcs7-signature";
  
      private static final HtmlToTextConverter htmlConverter = new HtmlToTextConverter();
      private static final Logger log = Logger.getLogger(MailUtils.class);
  
      /**
       * The content transfer encoding header, which is used to identify whether a part is base64 encoded.
       */
      private static final String CONTENT_TRANSFER_ENCODING_HEADER = "Content-Transfer-Encoding";
  
      /**
       * Content header id
       */
      private static final String CONTENT_ID_HEADER = "Content-ID";
  
      /**
       * Very simple representation of a mail attachment after it has been
       * extracted from a message.
       */
      public static class Attachment {
          private final String contentType;
          private final String fileName;
          private final byte[] contents;
  
          public Attachment(String contentType, String fileName, byte[] contents)
          {
              this.contentType = contentType;
              this.fileName = fileName;
              this.contents = contents;
          }
  
          public String getContentType()
          {
              return contentType;
          }
  
          public byte[] getContents()
          {
              return contents;
          }
  
          public String getFilename()
         {
             return fileName;
         }
     }
 
     /**
      * Parse addresses from a comma (and space) separated string into the proper array
      */
     public static InternetAddress[] parseAddresses(String addresses) throws AddressException
     {
         List<InternetAddress> list = new ArrayList<InternetAddress>();
         list.clear();
         StringTokenizer st = new StringTokenizer(addresses, ", ");
         while (st.hasMoreTokens())
         {
             list.add(new InternetAddress(st.nextToken()));
         }
         return list.toArray(new InternetAddress[list.size()]);
     }
 
     /**
      * Get the body of the message as a String. The algorithm for finding the body is as follows:
      *
      * <ol><li>If the message is a single part, and that part is text/plain, return it.
      *     <li>If the message is a single part, and that part is text/html, convert it to
      *         text (stripping out the HTML) and return it.
      *     <li>If the message is multi-part, return the first text/plain part that isn't marked
      *         explicitly as an attachment.
      *     <li>If the message is multi-part, but does not contain any text/plain parts, return
      *         the first text/html part that isn't marked explicitly as an attachment, converting
      *         it to text and stripping the HTML.
      *     <li>If nothing is found in any of the steps above, return null.
      * </ol>
      *
      * <p>Note: If the message contains nested multipart parts, an HTML part nested at a higher level will
      * take precedence over a text part nested deeper.
      *
      * @param message The message to retrieve the body from
      * @return The message body, or null if the message could not be parsed
      * @throws javax.mail.MessagingException If there was an error getting the content from the message
      */
     public static String getBody(Message message) throws MessagingException
     {
         try
         {
             String content = extractTextFromPart(message);
                 
             if (content == null)
             {
                 if (message.getContent() instanceof Multipart)
                 {
                     content = getBodyFromMultipart((Multipart) message.getContent());
                 }
             }
 
             if (content == null)
             {
                 //didn't match anything above
                 log.info("Could not find any body to extract from the message");
             }
             
             return content;
         }
         catch (ClassCastException cce)
         {
             log.info("Exception getting the content type of message - probably not of type 'String': " + cce.getMessage());
             return null;
         }
         catch (IOException e)
         {
             log.info("IOException whilst getting message content " + e.getMessage());
             return null;
         }
     }
 
     /**
      * Gets all parts of a message that are attachments rather than alternative inline bits.
      *
      * @param message the message from which to extract the attachments
      * @return an array of the extracted attachments
      */
     public static Attachment[] getAttachments(Message message) throws MessagingException, IOException
     {
         List<Attachment> attachments = new ArrayList<Attachment>();
 
         if (message.getContent() instanceof Multipart)
         {
             addAttachments(attachments, (Multipart)message.getContent());
         }
 
         return attachments.toArray(new Attachment[attachments.size()]);
     }
 
     private static void addAttachments(List<Attachment> attachments, Multipart parts) throws MessagingException, IOException
     {
         for (int i = 0, n = parts.getCount(); i < n; i++)
         {
             BodyPart part = parts.getBodyPart(i);
 
             if (isAttachment(part))
             {
                 InputStream content = part.getInputStream();
                 String contentType = part.getContentType();
 
                 attachments.add(new Attachment(contentType, part.getFileName(), toByteArray(content)));
             }
             else
             {
                 try
                 {
                     if (part.getContent() instanceof Multipart)
                     {
                         addAttachments(attachments, (Multipart) part.getContent());
                     }
                 }
                 catch (UnsupportedEncodingException e)
                 {
                     // ignore because it's probably not a multipart part anyway
                     // if the encoding is unsupported
                     log.warn("Unsupported encoding found for part while trying to discover attachments. "
                             + "Attachment will be ignored.", e);
                 }
             }
         }
     }
 
     private static boolean isAttachment(BodyPart part)
             throws MessagingException
     {
         return Part.ATTACHMENT.equals(part.getDisposition()) || Part.INLINE.equals(part.getDisposition())
 				|| (part.getDisposition() == null && part.getFileName() != null);
     }
 
     /**
      * Convert the contents of an input stream into a byte array.
      *
      * @param in
      * @return the contents of that stream as a byte array.
      */
     private static byte[] toByteArray(InputStream in) throws IOException
     {
         ByteArrayOutputStream out = new ByteArrayOutputStream();
         byte[] buf = new byte[512];
         int count;
         while ((count = in.read(buf)) != -1)
         {
             out.write(buf, 0, count);
         }
 
         out.close();
         return out.toByteArray();
     }
 
     /**
      * @return true if at least one of the recipients matches the email address given.
      */
     public static boolean hasRecipient(String matchEmail, Message message) throws MessagingException
     {
         Address[] addresses = message.getAllRecipients();
 
         if (addresses == null || addresses.length == 0)
             return false;
 
         for (int i = 0; i < addresses.length; i++)
         {
             InternetAddress email = (InternetAddress) addresses[i];
 
             if (matchEmail.compareToIgnoreCase(email.getAddress()) == 0)
                 return true;
         }
 
         return false;
     }
 
     /**
      * Returns a List<String> of trimmed non-null email addresses from the
      * given potentially dirty pile of addresses listed as senders on the
      * given message.
      * @param message the message from which to get senders.
      * @return a nice List<String> of email addresses.
      * @throws MessagingException if the senders can't be retrieved from message.
      */
     public static List<String> getSenders(Message message) throws MessagingException
     {
 
         ArrayList<String> senders = new ArrayList<String>();
         Address[] addresses = message.getFrom();
         if (addresses != null)
         {
             for (int i = 0; i < addresses.length; i++)
             {
                 if (addresses[i] instanceof InternetAddress)
                 {
                     InternetAddress addr = (InternetAddress) addresses[i];
                     // Trim down the email address to remove any whitespace etc.
                     String emailAddress = StringUtils.trimToNull(addr.getAddress());
                     if (emailAddress != null)
                     {
                         senders.add(emailAddress);
                     }
                 }
             }
         }
         return senders;
     }
 
     /**
      * Produces a mimebodypart object from an attachment file path. An attachment needs to be in this form to be attached
      * to an email for sending
      *
      * @param path
      * @return
      * @throws MessagingException
      */
     public static MimeBodyPart createAttachmentMimeBodyPart(String path) throws MessagingException
     {
         MimeBodyPart attachmentPart = new MimeBodyPart();
         DataSource source = new FileDataSource(path);
         attachmentPart.setDataHandler(new DataHandler(source));
 
         String fileName = extractFilenameFromPath(path);
 
         attachmentPart.setFileName(fileName);
         return attachmentPart;
     }
 
     private static String extractFilenameFromPath(String path) {
         if (path == null) return null;
         StringTokenizer st = new StringTokenizer(path, "\\/");
 
         String fileName;
         do
         {
             fileName = st.nextToken();
         }
         while (st.hasMoreTokens());
         return fileName;
     }
 
     public static MimeBodyPart createZippedAttachmentMimeBodyPart(String path) throws MessagingException
     {
         File tmpFile = null;
         String fileName = extractFilenameFromPath(path);
 
         try {
             tmpFile = File.createTempFile("atlassian", null);
             FileOutputStream fout = new FileOutputStream(tmpFile);
             ZipOutputStream zout = new ZipOutputStream(fout);
             zout.putNextEntry(new ZipEntry(fileName));
 
             InputStream in = new FileInputStream(path);
             final byte[] buffer = new byte[ BUFFER_SIZE ];
             int n = 0;
             while ( -1 != (n = in.read(buffer)) ) {
                 zout.write(buffer, 0, n);
             }
             zout.close();
             in.close();
             log.debug("Wrote temporary zip of attachment to " + tmpFile);
         } catch (FileNotFoundException e) {
             String err = "Couldn't find file '"+path+"' on server: "+e;
             log.error(err, e);
             MimeBodyPart mimeBodyPart = new MimeBodyPart();
             mimeBodyPart.setText(err);
             return mimeBodyPart;
         } catch (IOException e) {
             String err = "Error zipping log file '"+path+"' on server: "+e;
             log.error(err, e);
             MimeBodyPart mimeBodyPart = new MimeBodyPart();
             mimeBodyPart.setText(err);
             return mimeBodyPart;
         }
         MimeBodyPart attachmentPart = new MimeBodyPart();
         DataSource source = new FileDataSource(tmpFile);
         attachmentPart.setDataHandler(new DataHandler(source));
         attachmentPart.setFileName(fileName+".zip");
         attachmentPart.setHeader("Content-Type", "application/zip");
         return attachmentPart;
     }
 
     private static String getBodyFromMultipart(Multipart multipart) throws MessagingException, IOException
     {
         StringBuffer sb = new StringBuffer();
         getBodyFromMultipart(multipart, sb);
         return sb.toString();
     }
 
     private static void getBodyFromMultipart(Multipart multipart, StringBuffer sb) throws MessagingException, IOException
     {
         String multipartType = multipart.getContentType();
 
         // if an multipart/alternative type we just get the first text or html content found
         if(multipartType != null && compareContentType(multipartType, MULTIPART_ALTERNATE_CONTENT_TYPE))
         {
             BodyPart part = getFirstInlinePartWithMimeType(multipart, TEXT_CONTENT_TYPE);
             if(part != null)
             {
                 appendMultipartText(extractTextFromPart(part), sb);
             }
             else
             {
                 part = getFirstInlinePartWithMimeType(multipart, HTML_CONTENT_TYPE);
                 appendMultipartText(extractTextFromPart(part), sb);
             }
             return;
         }
 
         // otherwise assume multipart/mixed type and construct the contents by retrieving all text and html
         for (int i = 0, n = multipart.getCount(); i < n; i++)
         {
             BodyPart part = multipart.getBodyPart(i);
             String contentType = part.getContentType();
 
             if (!Part.ATTACHMENT.equals(part.getDisposition()) && contentType != null)
             {
                 try
                 {
                     String content = extractTextFromPart(part);
                     if (content != null)
                     {
                         appendMultipartText(content, sb);
                     }
                     else if(part.getContent() instanceof Multipart)
                     {
                         getBodyFromMultipart((Multipart) part.getContent(), sb);
                     }
                 }
                 catch (IOException exception)
                 {
                     // We swallow the exception because we want to allow processing to continue
                     // even if there is a bad part in one part of the message
                     log.warn("Error retrieving content from part '" + exception.getMessage() + "'", exception);
                 }
             }
         }
     }
 
     private static void appendMultipartText(String content, StringBuffer sb) throws IOException, MessagingException
     {
         if (content != null)
         {
             if(sb.length() > 0) sb.append("\n");
             sb.append(content);
         }
     }
 
     private static String extractTextFromPart(Part part) throws IOException, MessagingException,
             UnsupportedEncodingException
     {
         if (part == null)
             return null;
 
         String content = null;
 
         if (isPartPlainText(part))
         {
             try
             {
                 content = (String) part.getContent();
             }
             catch (UnsupportedEncodingException e)
             {
                 // If the encoding is unsupported read the content with default encoding
                 log.warn("Found unsupported encoding '" + e.getMessage() + "'. Reading content with "
                         + DEFAULT_ENCODING + " encoding.");
                 content = getBody(part, DEFAULT_ENCODING);
             }
         }
         else if (isPartHtml(part))
         {
             content = htmlConverter.convert((String) part.getContent());
         }
 
         if (content == null)
         {
             log.warn("Unable to extract text from MIME part with Content-Type '" + part.getContentType());
         }
 
         return content;
     }
 
     private static String getBody(Part part, String charsetName) throws UnsupportedEncodingException,
             IOException, MessagingException
     {
         Reader input = null;
         StringWriter output = null;
         try
         {
             input = new BufferedReader(new InputStreamReader(part.getInputStream(), charsetName));
             output = new StringWriter();
             IOUtils.copy(input, output);
             return output.getBuffer().toString();
         }
         finally
         {
             IOUtils.closeQuietly(input);
             IOUtils.closeQuietly(output);
         }
     }
 
     private static BodyPart getFirstInlinePartWithMimeType(Multipart multipart, String mimeType) throws MessagingException
     {
         for (int i = 0, n = multipart.getCount(); i < n; i++)
         {
             BodyPart part = multipart.getBodyPart(i);
             String contentType = part.getContentType();
             if (!Part.ATTACHMENT.equals(part.getDisposition()) && contentType != null && compareContentType(contentType, mimeType))
             {
                 return part;
             }
         }
         return null;
     }
 
     private static boolean compareContentType(String contentType, String mimeType)
     {
         return contentType.toLowerCase().startsWith(mimeType);
     }
 
 
     /**
      * Tests if a particular part content type is text/html.
      *
      * @param part The part being tested.
      * @return true if the part content type is text/html
      * @throws MessagingException if javamail complains
      */
     static public boolean isPartHtml(final Part part) throws MessagingException
     {
         final String contentType = MailUtils.getContentType(part);
         return HTML_CONTENT_TYPE.equalsIgnoreCase(contentType);
     }
 
     /**
      * Tests if the provided part content type is text/plain.
      *
      * @param part The part being tested.
      * @return true if the part content type is text/plain
      * @throws MessagingException if javamail complains
      */
     static public boolean isPartPlainText(final Part part) throws MessagingException
     {
         final String contentType = MailUtils.getContentType(part);
         return TEXT_CONTENT_TYPE.equalsIgnoreCase(contentType);
     }
 
     /**
      * Tests if the provided part's content type is message/rfc822
      *
      * @param part The part being tested.
      * @return true if the part content type is message/rfc822
      * @throws MessagingException if javamail complains
      */
     static public boolean isPartMessageType(final Part part) throws MessagingException
     {
         // currently, only "message/rfc822" content type is supported
         final String contentType = MailUtils.getContentType(part);
         return MESSAGE_CONTENT_TYPE.equalsIgnoreCase(contentType);
     }
 
     /**
      * Tests if the provided part's content type is multipart/related
      *
      * @param part The part being tested.
      * @return true if the part content type is multipart/related
      * @throws MessagingException if javamail complains
      */
     static public boolean isPartRelated(final Part part) throws MessagingException
     {
         final String contentType = getContentType(part);
         return MULTIPART_RELATED_CONTENT_TYPE.equalsIgnoreCase(contentType);
     }
 
     /**
      * Helper which returns the pure mime/subMime content type less any other extra parameters which may
      * accompany the header value.
      *
      * @param part the mail part to extract the content-type from.
      * @return the pure mime/subMime type
      * @throws MessagingException if retrieving the part's Content-Type header fails
      */
     static public String getContentType(final Part part) throws MessagingException
     {
         checkPartNotNull(part);
 
         final String contentType = part.getContentType();
         return getContentType(contentType);
     }
 
     /**
      * Helper which extracts the content type from a header value removing parameters and so on.
      *
      * @param headerValue The header value.
      * @return The actual content type
      */
     static public String getContentType(final String headerValue)
     {
         checkHeaderValue(headerValue);
 
         String out = headerValue;
 
         final int semiColon = headerValue.indexOf(';');
         if (-1 != semiColon)
         {
             out = headerValue.substring(0, semiColon);
         }
 
         return out.trim();
     }
 
     static private void checkHeaderValue(final String headerValue)
     {
         Validate.notEmpty(headerValue);
     }
 
     /**
      * Tests if the content of the part content is empty.  The definition of empty depends on whether the content is text
      * or binary.
      * <p/>
      * Text content for content types like plain/text and html/text is defined as being empty if it contains an empty string
      * after doing a trim(). If the string contains 50 spaces it is still empty whilst a string with a solitary "a"
      * isnt.
      * <p/>
      * For binary content (like images) if the content contains 0 bytes it is empty whilst anything with 1 or more bytes
      * is NOT considered empty.
      *
      * @param part a mail part - may or may not have content.
      * @return true/false if the content is deemed empty as per above rules.
      * @throws MessagingException if retrieving content fails.
      * @throws IOException        if retrieving content fails or reading content input stream fails.
      */
     static public boolean isContentEmpty(final Part part) throws MessagingException, IOException
     {
         checkPartNotNull(part);
 
         boolean definitelyEmpty = false;
         final Object content = part.getContent();
         if (null == content)
         {
             definitelyEmpty = true;
         }
         else
         {
             if (content instanceof String)
             {
                 final String stringContent = (String) content;
                 definitelyEmpty = StringUtils.isBlank(stringContent);
             }
 
             if (content instanceof InputStream)
             {
                 final InputStream inputStream = (InputStream) content;
                 try
                 {
 
                     // try and read a byte.. it we get one its not empty, if we dont its empty.
                     final int firstByte = inputStream.read();
                     definitelyEmpty = -1 == firstByte;
 
                 }
                 finally
                 {
                     IOUtils.closeQuietly(inputStream);
                 }
             }
         }
 
         return definitelyEmpty;
     }
 
     /**
      * Asserts that the part parameter is not null, throwing a NullPointerException if the part parameter is null.
      *
      * @param part The parameter part
      */
     static private void checkPartNotNull(final Part part)
     {
         Validate.notNull(part, "part should not be null.");
     }
 
     /**
      * This method uses a number of checks to determine if the given part actually represents an inline (typically image) part.
      * Some email clients (aka lotus notes) dont appear to correctly set the disposition to inline so a number of
      * additional checks are required, hence the multi staged approached.
      * <p/>
      * eg. inline images from notes wont have a inline disposition but will have a content id and will also have their
      * content base64 encoded. This approach helps us correctly identify inline images or other binary parts.
      *
      * @param part The part being tested.
      * @return True if the part is inline false in all other cases.
      * @throws MessagingException as thrown by java mail
      */
     static public boolean isPartInline(final Part part) throws MessagingException
     {
         checkPartNotNull(part);
 
         boolean inline = false;
 
         // an inline part is only considered inline if its also got a filename...
         final String disposition = part.getDisposition();
         if (Part.INLINE.equalsIgnoreCase(disposition))
         {
             final String file = part.getFileName();
             if(!StringUtils.isBlank(file))
             {
                 inline = true;
             }
             return inline;
         }
 
         final boolean gotContentId = MailUtils.hasContentId(part);
         if (!gotContentId)
         {
             return false;
         }
         final boolean gotBase64 = MailUtils.isContentBase64Encoded(part);
         if (!gotBase64)
         {
             return false;
         }
 
         return true;
     }
 
     static private boolean hasContentId(final Part part) throws MessagingException
     {
         boolean gotContentId = false;
         final String[] contentIds = part.getHeader(MailUtils.CONTENT_ID_HEADER);
         if (null != contentIds)
         {
             for (int i = 0; i < contentIds.length; i++)
             {
                 final String contentId = contentIds[i];
                 if (contentId != null && contentId.length() > 0)
                 {
                     gotContentId = true;
                     break;
                 }
             } // for
         }
         return gotContentId;
     }
 
     /**
      * Checks if a part's content is base64 encoded by scanning for a content transfer encoding header value.
      *
      * @param part THe part being tested.
      * @return True if the content is base 64 encoded, false in all other cases.
      * @throws MessagingException if javamail complains
      */
     static private boolean isContentBase64Encoded(final Part part) throws MessagingException
     {
         boolean gotBase64 = false;
         final String[] contentTransferEncodings = part.getHeader(CONTENT_TRANSFER_ENCODING_HEADER);
         if (null != contentTransferEncodings)
         {
             for (int i = 0; i < contentTransferEncodings.length; i++)
             {
                 final String contentTransferEncoding = contentTransferEncodings[i];
                 if ("base64".equals(contentTransferEncoding))
                 {
                     gotBase64 = true;
                     break;
                 }
             }
         }
 
         return gotBase64;
     }
 
     /**
      * Tests if the provided part is an attachment. Note this method does not test if the content is empty etc it merely
      * tests whether or not the part is an attachment of some sort.
      *
      * @param part The part being tested.
      * @throws MessagingException if javamail complains
      * @returns True if the part is an attachment otherwise returns false
      */
     static public boolean isPartAttachment(final Part part) throws MessagingException
     {
         checkPartNotNull(part);
         return Part.ATTACHMENT.equalsIgnoreCase(part.getDisposition());
     }
 
     /**
      * This method may be used to fix any mime encoded filenames that have been returned by javamail.
      * No harm can occur from calling this method unnecessarily except for wasting a few cpu cycles...
      * <p/>
      * Very probably a MIME-encoded filename - see http://java.sun.com/products/javamail/FAQ.html#encodefilename
      *
      * @param filename
      * @return The fixed filename.
      * @throws IOException {@see MimeUtility#decodeText}
      */
     static public String fixMimeEncodedFilename(final String filename) throws IOException
     {
         String newFilename = filename;
         if (filename.startsWith("=?") || filename.endsWith("?="))
         {
             newFilename = MimeUtility.decodeText(filename);
         }
         return newFilename;
     }
 
 
     /**
      * Tests if a part is actually a signature. This is required to fix JRA-9933.
      *
      * @param part a mail part. The part is assumed to have a content-type header.
      * @return true if the content-type header matches the standard PKCS7 mime types
      * @throws MessagingException if retrieving the Content-Type from the part fails.
      */
     static public boolean isPartSignaturePKCS7(final Part part) throws MessagingException
     {
         MailUtils.checkPartNotNull(part);
         final String contentType = MailUtils.getContentType(part).toLowerCase(Locale.getDefault());
         return contentType.startsWith(CONTENT_TYPE_PKCS7) || contentType.startsWith(CONTENT_TYPE_X_PKCS7);
     }
 
     /**
      * Get the local host name from InetAddress and return it in a form suitable for use in an email address or Message-ID.
      * <p>
      * Inspired by {@link javax.mail.internet.InternetAddress#getLocalAddress(javax.mail.Session)} and required because
      * {@link javax.mail.internet.InternetAddress#getLocalHostName()} is private.
      */
     @SuppressWarnings ("UnusedDeclaration")
     public static String getLocalHostName()
     {
         String host = null;
         InetAddress localHostAddress;
         try
         {
             localHostAddress = InetAddress.getLocalHost();
         }
         catch (UnknownHostException e)
         {
             return "localhost";
         }
         if (localHostAddress != null) {
             host = localHostAddress.getHostName();
             if (host != null && host.length() > 0 && isInetAddressLiteral(host))
             {
                 // required for an email address, not sure if it is required for a Message-ID, but no harm and this is
                 // what JavaMail would do.
                 host = '[' + host + ']';
             }
         }
         if (host == null)
             return "localhost";
         else
             return host;
     }
 
     /**
      * Is the address an IPv4 or IPv6 address literal, which needs to
      * be enclosed in "[]" in an email address?  IPv4 literals contain
      * decimal digits and dots, IPv6 literals contain hex digits, dots,
      * and colons.  We're lazy and don't check the exact syntax, just
      * the allowed characters; strings that have only the allowed
      * characters in a literal but don't meet the syntax requirements
      * for a literal definitely can't be a host name and thus will fail
      * later when used as an address literal.
      *
      * (Copied from javax.mail.internet.InternetAddress)
      */
     private static boolean isInetAddressLiteral(String addr)
     {
         boolean sawHex = false, sawColon = false;
         for (int i = 0; i < addr.length(); i++) {
             char c = addr.charAt(i);
             if (c >= '0' && c <= '9')
                 ;	// digits always ok
             else if (c == '.')
                 ;	// dot always ok
             else if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'))
                 sawHex = true;	// need to see a colon too
             else if (c == ':')
                 sawColon = true;
             else
                 return false;	// anything else, definitely not a literal
         }
         return !sawHex || sawColon;
     }
 
 }