/ 
Mail-Box-2.003
River stage one • 8 direct dependents • 8 total dependents
/ Mail::Box::MH

NAME

Mail::Box::MH - handle folders with a file per message.

CLASS HIERARCHY

Mail::Box::MH
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. The working of MH-messages are described in Mail::Box::MH::Message.

METHOD INDEX

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

MB addMessage  MESSAGE               MR log [LEVEL [,STRINGS]]
MB addMessages MESSAGE [, MESS...    MB message INDEX [,MESSAGE]
MB allMessageIds                     MB messageId MESSAGE-ID [,MESS...
MB close OPTIONS                     MB messages
MB create FOLDERNAME [, OPTIONS]     MB modified [BOOLEAN]
MB current [NUMBER|MESSAGE|MES...    MB name
MB delete                               new OPTIONS
   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

The extra methods for extension writers:

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

Methods prefixed with an abbreviation are described in the following manual-pages:

MB = L<Mail::Box>
MR = L<Mail::Reporter>

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_index        Mail::Box::MH      0
labels_filename   Mail::Box::MH      foldername.'/.mh_sequence'
extract           Mail::Box          10kB
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::Mbox. Common users of folders you will not specify these:

OPTION            DEFINED BY         DEFAULT
body_type         Mail::Box::MH      <see below>
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::MH      '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
lock_type         Mail::Box          'DOTLOCK'
multipart_type    Mail::Box          'Mail::Message::Body::Multipart'
manager           Mail::Box          undef
message_type      Mail::Box          'Mail::Box::MH::Message'
organization      Mail::Box          'DIRECTORY'
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.

  • head_delayed_type => CLASS

    The headers which are delayed: which will be read from file when it is needed, but not before.

  • 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.

The body_type options for Mbox folders defaults to:

sub determine_body_type($$)
{   my $head = shift;
    my $size = shift || 0;
    'Mail::Message::Body::' . ($size > 10000 ? 'File' : 'Lines');
}

which will cause messages larger than 10kB to be stored in files, and smaller files in memory.

directory

Returns the directory related to this folder.

Example:

print $folder->directory;

METHODS for extension writers

folderToDirectory FOLDERNAME, FOLDERDIR

(class method) Translate a foldername into a filename, with use of the FOLDERDIR to replace a leading =.

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.

readMessageFilenames DIRECTORY

Returns a list of all filenames which are found in this folder directory and represent a message. Message files are recognized by having a number as name.

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.

readAllHeaders

Force all messages to be read at least till their header information is known.

IMPLEMENTATION

The explanation is complicated, but for normal use you should bother yourself with all details.

How MH-folders work

MH-type folders use a directory to store the messages of one folder. Each message is stored in a seperate 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 as threads is desired.

So, each message is written in a seperate file. The file-names 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.

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.

Delayed loading

SEE ALSO

Mail::Box-Overview

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 2.003.

Copyright (c) 2001 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.