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Mail-Box-2.017
River stage one • 8 direct dependents • 8 total dependents
/ Mail::Box::MH

NAME

Mail::Box::MH - handle MH folders

CLASS HIERARCHY

 Mail::Box::MH
 is a Mail::Box::Dir
 is a Mail::Box
 is a Mail::Reporter

SYNOPSIS

 use Mail::Box::MH;
 my $folder = new Mail::Box::MH folder => $ENV{MAIL}, ...;

DESCRIPTION

This documentation describes how MH mailboxes work, and what you can do with the MH folder object Mail::Box::MH. Please read Mail::Box-Overview and Mail::Box first.

The internal organization and details are found at the bottom of this manual-page.

METHOD INDEX

Methods prefixed with an abbreviation are described in Mail::Box (MB), Mail::Reporter (MR), Mail::Box::Dir (MBD).

The general methods for Mail::Box::MH objects:

   MB addMessage  MESSAGE               MB message INDEX [,MESSAGE]
   MB addMessages MESSAGE [, MESS...    MB messageId MESSAGE-ID [,MESS...
   MB close OPTIONS                     MB messageIds
   MB copyTo FOLDER, OPTIONS            MB messages ['ALL',RANGE,'ACTI...
   MB create FOLDERNAME [, OPTIONS]     MB modified [BOOLEAN]
   MB current [NUMBER|MESSAGE|MES...    MB name
   MB delete                               new OPTIONS
  MBD directory                         MB openSubFolder NAME [,OPTIONS]
   MR errors                            MR report [LEVEL]
   MB find MESSAGE-ID                   MR reportAll [LEVEL]
   MB listSubFolders OPTIONS            MR trace [LEVEL]
   MB locker                            MR warnings
   MR log [LEVEL [,STRINGS]]            MB writable

The extra methods for extension writers:

   MR AUTOLOAD                          MB openRelatedFolder OPTIONS
   MB DESTROY                           MB organization
   MB appendMessages OPTIONS            MB read OPTIONS
   MB clone OPTIONS                    MBD readAllHeaders
   MB coerce MESSAGE                   MBD readMessageFilenames DIRECTORY
   MB determineBodyType MESSAGE, ...    MB readMessages OPTIONS
  MBD folderToDirectory FOLDERNAM...    MB scanForMessages MESSAGE, ME...
   MB folderdir [DIR]                   MB sort PREPARE, COMPARE, LIST
   MB foundIn [FOLDERNAME], OPTIONS     MB storeMessage MESSAGE
      highestMessageNumber              MB timespan2seconds TIME
   MR inGlobalDestruction               MB toBeThreaded MESSAGES
      index                             MB toBeUnthreaded MESSAGES
      labels                            MB update OPTIONS
   MB lineSeparator [STRING|'CR'|...    MB updateMessages OPTIONS
   MR logPriority LEVEL                 MB write OPTIONS
   MR logSettings                          writeMessages [OPTIONS]
   MR notImplemented

METHODS

new OPTIONS

Create a new folder. The are many options which are taken from other objects. For some, different options are set. For MH-specific options see below, but first the full list.

 OPTION            DEFINED BY         DEFAULT
 access            Mail::Box          'r'
 create            Mail::Box          0
 folder            Mail::Box          $ENV{MAIL}
 folderdir         Mail::Box          <no default>
 head_wrap         Mail::Box          72
 index_filename    Mail::Box::MH      foldername.'/.index'
 keep_dups         Mail::Box          0
 keep_index        Mail::Box::MH      0
 labels_filename   Mail::Box::MH      foldername.'/.mh_sequence'
 extract           Mail::Box          10kB
 lock_type         Mail::Box          'DOTLOCK'
 lock_file         Mail::Box          foldername.'/.lock'
 lock_timeout      Mail::Box          3600    (1 hour)
 lock_wait         Mail::Box          10      (seconds)
 log               Mail::Reporter     'WARNINGS'
 remove_when_empty Mail::Box          1
 save_on_exit      Mail::Box          1
 trace             Mail::Reporter     'WARNINGS'
 trusted           Mail::Box          <depends on folder location>

Only useful to write extension to Mail::Box::MH. Common users of folders you will not specify these:

 OPTION            DEFINED BY         DEFAULT
 body_type         Mail::Box::Dir     <see Mail::Box::Dir>
 body_delayed_type Mail::Box          'Mail::Message::Body::Delayed'
 coerce_options    Mail::Box          []
 field_type        Mail::Box          undef
 head_type         Mail::Box          'Mail::Message::Head::Complete'
 head_delayed_type Mail::Box          'Mail::Message::Head::Delayed'
 index             Mail::Box::MH      undef
 index_type        Mail::Box::MH      'Mail::Box::MH::Index'
 labels            Mail::Box::MH      undef
 labels_type       Mail::Box::MH      'Mail::Box::MH::Labels'
 locker            Mail::Box          undef
 multipart_type    Mail::Box          'Mail::Message::Body::Multipart'
 manager           Mail::Box          undef
 message_type      Mail::Box          'Mail::Box::MH::Message'
 realhead_type     Mail::Box          'Mail::Message::Head'

MH specific options:

  • keep_index => BOOL

    Keep an index file of the specified mailbox, one file per directory. Using an index file will speed up things considerably, because it avoids reading all the message files the moment that you open the folder. When you open a folder, you can use the index file to retrieve information such as the subject of each message, instead of having to read possibly thousands of messages.

  • index_filename => FILENAME

    The FILENAME which is used in each directory to store the headers of all mails. The filename shall not contain a directory path. (e.g. Do not use /usr/people/jan/.index, nor subdir/.index, but say .index.)

  • index => OBJECT

    You may specify an OBJECT of a type which extends Mail::Box::MH::Index (at least implements the get() method), as alternative for an index file reader as created by Mail::Box::MH.

  • labels_filename => FILENAME

    In MH-folders, messages can be labeled, for instance based on the sender or whether it is read or not. This status is kept in a file which is usually called .mh_sequences, but that name can be overruled with this flag.

  • labels => OBJECT

    You may specify an OBJECT of a type which extends Mail::Box::MH::Labels (at least implements the get() method), as alternative for labels file reader as created by Mail::Box::MH.

METHODS for extension writers

highestMessageNumber

Returns the highest number which is used in the folder to store a file. This method may be called when the folder is read (then this number can be derived without file-system access), but also when the folder is not read (yet).

index

Create a index reader/writer object.

labels

Create a label reader/writer object.

writeMessages [OPTIONS]

Write all messages to the folder-file.

 OPTION            DEFINED BY         DEFAULT
 force             Mail::Box          <true>
 head_wrap         Mail::Box          72
 keep_deleted      Mail::Box          <false>
 renumber          Mail::Box::MH      <true>
 save_deleted      Mail::Box          <false>

MH specific options:

  • renumber => BOOL

    Permit renumbering of message. Bij default this is true, but for some unknown reason, you may be thinking that messages should not be renumbered.

IMPLEMENTATION

How MH-folders work

MH-type folders use a directory to store the messages of one folder. Each message is stored in a separate file. This seems useful, because changes in a folder change only a few of these small files, in contrast with file-based folders where changes in a folder cause rewrites of huge folder files.

However, MH-based folders perform very bad if you need header information of all messages. For instance, if you want to have full knowledge about all message-threads (see Mail::Box::Thread::Manager) in the folder, it requires to read all header lines in all message files. And usually, reading your messages in threads is desired.

So, each message is written in a separate file. The filenames are numbers, which count from 1. Next to these message files, a directory may contain a file named .mh_sequences, storing labels which relate to the messages. Furthermore, a folder-directory may contain sub-directories, which are seen as sub-folders.

Labels

User actions on a message are flagged with a label. When the folder is opened, these flags are read from the .mh_sequences file. When the folder is closed that file gets updated. Status and X-Status lines in the message headers -as used by Mbox folders- are only looked at when new messages are added to the folder. These lines are only updated when a MH message has to be written to a folder for some reason.

This implementation

This implementation supports the .mh-sequences file and sub-folders. Next to this, considerable effort it made to avoid reading each message-file. This should boost performance of the Mail::Box module over other Perl-modules which are able to read folders.

Folder-types which store their messages each in one file, together in one directory, are bad for performance. Consider that you want to know the subjects of all messages, while browser through a folder with your mail-reading client. This would cause all message-files to be read.

Mail::Box::MH has two ways to try improve performance. You can use an index-file, and use on delay-loading. The combination performs even better. Both are explained in the next sections.

An index-file

If you specify keep_index as option to the folder creation method new(), then all header-lines of all messages from the folder which have been read once, will also be written into one dedicated index-file (one file per folder). The default filename is .index

However, index-files are not supported by any other reader which supports MH (as far as I know). If you read the folders with such I client, it will not cause unrecoverable conflicts with this index-file, but at most be bad for performance.

If you do not (want to) use an index-file, then delay-loading may save your day.

SEE ALSO

Mail::Box-Overview

For support and additional documentation, see http://perl.overmeer.net/mailbox/

AUTHOR

Mark Overmeer (mailbox@overmeer.net). All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

VERSION

This code is beta, version 2.017.

Copyright (c) 2001-2002 Mark Overmeer. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.