
=head1 NAME

Mail::Box::MH - handle MH folders


=head1 INHERITANCE

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


=head1 SYNOPSIS

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


=head1 DESCRIPTION

This documentation describes how MH mailboxes work, and what you
can do with the MH folder object C<Mail::Box::MH>.


=head1 OVERLOADED


overload: B<"">

=over 4

See L<Mail::Box/"OVERLOADED">

=back

overload: B<@{}>

=over 4

See L<Mail::Box/"OVERLOADED">

=back

overload: B<cmp>

=over 4

See L<Mail::Box/"OVERLOADED">

=back


=head1 METHODS


=head2 Constructors


$obj-E<gt>B<create>(FOLDERNAME, OPTIONS)

Mail::Box::MH-E<gt>B<create>(FOLDERNAME, OPTIONS)

=over 4

 Option     Defined in    Default
 folderdir  L<Mail::Box>  undef  

. folderdir DIRECTORY

=back

Mail::Box::MH-E<gt>B<new>(OPTIONS)

=over 4

 Option             Defined in       Default                                                         
 access             L<Mail::Box>     C<'r'>                                                          
 body_delayed_type  L<Mail::Box>     L<Mail::Message::Body::Delayed|Mail::Message::Body::Delayed>    
 body_type          L<Mail::Box>     L<Mail::Message::Body::Lines|Mail::Message::Body::Lines>        
 coerce_options     L<Mail::Box>     C<[]>                                                           
 create             L<Mail::Box>     <false>                                                         
 extract            L<Mail::Box>     C<10240>                                                        
 field_type         L<Mail::Box>     undef                                                           
 fix_headers        L<Mail::Box>     <false>                                                         
 folder             L<Mail::Box>     C<$ENV{MAIL}>                                                   
 folderdir          L<Mail::Box>     C<$ENV{HOME}/.mh>                                               
 head_delayed_type  L<Mail::Box>     L<Mail::Message::Head::Delayed|Mail::Message::Head::Delayed>    
 head_type          L<Mail::Box>     L<Mail::Message::Head::Complete|Mail::Message::Head::Complete>  
 index                               undef                                                           
 index_filename                      <foldername>C</.index>                                          
 index_type                          L<Mail::Box::MH::Index|Mail::Box::MH::Index>                    
 keep_dups          L<Mail::Box>     <false>                                                         
 keep_index                          0                                                               
 labels                              undef                                                           
 labels_filename                     <foldername>C</.mh_sequence>                                    
 labels_type                         L<Mail::Box::MH::Labels|Mail::Box::MH::Labels>                  
 lock_file          L<Mail::Box>     <index_file>                                                    
 lock_timeout       L<Mail::Box>     1 hour                                                          
 lock_type          L<Mail::Box>     L<Mail::Box::Locker::DotLock|Mail::Box::Locker::DotLock>        
 lock_wait          L<Mail::Box>     10 seconds                                                      
 locker             L<Mail::Box>     undef                                                           
 log                L<Mail::Reporter>  C<'WARNINGS'>                                                   
 manager            L<Mail::Box>     undef                                                           
 message_type       L<Mail::Box>     L<Mail::Box::Message|Mail::Box::Message>                        
 multipart_type     L<Mail::Box>     L<Mail::Message::Body::Multipart|Mail::Message::Body::Multipart>
 remove_when_empty  L<Mail::Box>     <true>                                                          
 save_on_exit       L<Mail::Box>     <true>                                                          
 trace              L<Mail::Reporter>  C<'WARNINGS'>                                                   
 trusted            L<Mail::Box>     <depends on folder location>                                    

. access MODE

. body_delayed_type CLASS

. body_type CLASS|CODE

. coerce_options ARRAY

. create BOOLEAN

. extract INTEGER | CODE | METHOD | 'LAZY'|'ALWAYS'

. field_type CLASS

. fix_headers BOOLEAN

. folder FOLDERNAME

. folderdir DIRECTORY

. head_delayed_type CLASS

. head_type CLASS

. index OBJECT

=over 4

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

=back

. index_filename FILENAME

=over 4

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
C</usr/people/jan/.index>, nor C<subdir/.index>, but say C<.index>.)

=back

. index_type CLASS

. keep_dups BOOLEAN

. keep_index BOOLEAN

=over 4

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.

=back

. labels OBJECT

=over 4

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

=back

. labels_filename FILENAME

=over 4

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 C<.mh_sequences>, but that name can
be overruled with this flag.

=back

. labels_type CLASS

. lock_file FILENAME

. lock_timeout SECONDS

. lock_type CLASS|STRING

. lock_wait SECONDS

. locker OBJECT

. log LEVEL

. manager MANAGER

. message_type CLASS

. multipart_type CLASS

. remove_when_empty BOOLEAN

. save_on_exit BOOLEAN

. trace LEVEL

. trusted BOOLEAN

=back

=head2 The folder


$obj-E<gt>B<addMessage>(MESSAGE)

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<addMessages>(MESSAGE [, MESSAGE, ...])

=over 4

See L<Mail::Box/"The folder">

=back

Mail::Box::MH-E<gt>B<appendMessages>(OPTIONS)

=over 4

Append a message to a folder which is not open.

 Option    Defined in       Default   
 folder    L<Mail::Box>     <required>
 message   L<Mail::Box>     undef     
 messages  L<Mail::Box>     undef     

. folder FOLDERNAME

. message MESSAGE

. messages ARRAY-OF-MESSAGES

=back

$obj-E<gt>B<close>(OPTIONS)

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<copyTo>(FOLDER, OPTIONS)

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<delete>

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<directory>

=over 4

See L<Mail::Box::Dir/"The folder">

=back

$obj-E<gt>B<folderdir>([DIRECTORY])

=over 4

See L<Mail::Box/"The folder">

=back

Mail::Box::MH-E<gt>B<foundIn>([FOLDERNAME], OPTIONS)

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<name>

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<organization>

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<type>

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<update>(OPTIONS)

=over 4

See L<Mail::Box/"The folder">

=back

$obj-E<gt>B<url>

=over 4

See L<Mail::Box/"The folder">

=back

=head2 Folder flags


$obj-E<gt>B<isModified>

=over 4

See L<Mail::Box/"Folder flags">

=back

$obj-E<gt>B<modified>([BOOLEAN])

=over 4

See L<Mail::Box/"Folder flags">

=back

$obj-E<gt>B<writable>

=over 4

See L<Mail::Box/"Folder flags">

=back

=head2 The messages


$obj-E<gt>B<current>([NUMBER|MESSAGE|MESSAGE-ID])

=over 4

See L<Mail::Box/"The messages">

=back

$obj-E<gt>B<find>(MESSAGE-ID)

=over 4

See L<Mail::Box/"The messages">

=back

$obj-E<gt>B<message>(INDEX [,MESSAGE])

=over 4

See L<Mail::Box/"The messages">

=back

$obj-E<gt>B<messageId>(MESSAGE-ID [,MESSAGE])

=over 4

See L<Mail::Box/"The messages">

=back

$obj-E<gt>B<messageIds>

=over 4

See L<Mail::Box/"The messages">

=back

$obj-E<gt>B<messages>(['ALL',RANGE,'ACTIVE','DELETED',LABEL,!LABEL,FILTER])

=over 4

See L<Mail::Box/"The messages">

=back

$obj-E<gt>B<scanForMessages>(MESSAGE, MESSAGE-IDS, TIMESPAN, WINDOW)

=over 4

See L<Mail::Box/"The messages">

=back

=head2 Sub-folders


$obj-E<gt>B<listSubFolders>(OPTIONS)

Mail::Box::MH-E<gt>B<listSubFolders>(OPTIONS)

=over 4

See L<Mail::Box/"Sub-folders">

=back

$obj-E<gt>B<nameOfSubFolder>(NAME)

=over 4

See L<Mail::Box/"Sub-folders">

=back

$obj-E<gt>B<openRelatedFolder>(OPTIONS)

=over 4

See L<Mail::Box/"Sub-folders">

=back

$obj-E<gt>B<openSubFolder>(NAME, OPTIONS)

=over 4

See L<Mail::Box/"Sub-folders">

=back

=head2 Internals


$obj-E<gt>B<coerce>(MESSAGE)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<determineBodyType>(MESSAGE, HEAD)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<folderToDirectory>(FOLDERNAME, FOLDERDIR)

=over 4

See L<Mail::Box::Dir/"Internals">

=back

$obj-E<gt>B<highestMessageNumber>

=over 4

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).

=back

$obj-E<gt>B<index>

=over 4

Create a index reader/writer object.

=back

$obj-E<gt>B<labels>

=over 4

Create a label reader/writer object.

=back

$obj-E<gt>B<lineSeparator>([STRING|'CR'|'LF'|'CRLF'])

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<locker>

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<read>(OPTIONS)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<readMessageFilenames>(DIRECTORY)

=over 4

See L<Mail::Box::Dir/"Internals">

=back

$obj-E<gt>B<readMessages>(OPTIONS)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<storeMessage>(MESSAGE)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<toBeThreaded>(MESSAGES)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<toBeUnthreaded>(MESSAGES)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<updateMessages>(OPTIONS)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<write>(OPTIONS)

=over 4

See L<Mail::Box/"Internals">

=back

$obj-E<gt>B<writeMessages>(OPTIONS)

=over 4

 Option    Defined in       Default   
 messages  L<Mail::Box>     <required>
 renumber                   <true>    

. messages ARRAY

. renumber BOOLEAN

=over 4

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

=back

=back

=head2 Other methods


$obj-E<gt>B<timespan2seconds>(TIME)

Mail::Box::MH-E<gt>B<timespan2seconds>(TIME)

=over 4

See L<Mail::Box/"Other methods">

=back

=head2 Error handling


$obj-E<gt>B<AUTOLOAD>

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<defaultTrace>([LEVEL, [LEVEL])

Mail::Box::MH-E<gt>B<defaultTrace>([LEVEL, [LEVEL])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<errors>

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<log>([LEVEL [,STRINGS]])

Mail::Box::MH-E<gt>B<log>([LEVEL [,STRINGS]])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<logPriority>(LEVEL)

Mail::Box::MH-E<gt>B<logPriority>(LEVEL)

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<logSettings>

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<notImplemented>

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<report>([LEVEL])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<reportAll>([LEVEL])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<trace>([LEVEL])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<warnings>

=over 4

See L<Mail::Reporter/"Error handling">

=back

=head2 Cleanup


$obj-E<gt>B<DESTROY>

=over 4

See L<Mail::Box/"Cleanup">

=back

$obj-E<gt>B<inGlobalDestruction>

=over 4

See L<Mail::Reporter/"Cleanup">

=back



=head1 DIAGNOSTICS

I<Error:> Cannot append message without lock on $folder.

It is impossible to append one or more messages to the folder which is
not opened, because locking it failes.  The folder may be in use by
an other application, or you may need to specify some lock related
options (see L<new()|"METHODS">).

I<Error:> Cannot create MH folder $name: $!

For some reason, it is impossible to create the folder.  Check the permissions
and the name of the folder.  Does the path to the directory to be created
exist?

I<Error:> Cannot write folder $name without lock.

It is impossible to get a lock on the folder, which means that the changes
can not be made.  You may need to tune the lock related options which
are available at folder creation.

I<Warning:> Changes not written to read-only folder $self.

You have opened the folder read-only --which is the default set
by L<new(access)|Mail::Box/"Constructors">--, made modifications, and now want to close it.
Set L<close(force)|"The folder"> if you want to overrule the access mode, or close
the folder with L<close(write)|"The folder"> set to C<NEVER>.

I<Error:> Copying failed for one message.

For some reason, for instance disc full, removed by external process, or
read-protection, it is impossible to copy one of the messages.  Copying will
proceed for the other messages.

I<Error:> Destination folder $name is not writable.

The folder where the messages are copied to is not opened with write
access (see L<new(access)|Mail::Box/"Constructors">).  This has no relation with write permission
to the folder which is controled by your operating system.

I<Warning:> Different messages with id $msgid.

The message id is discovered more than once within the same folder, but the
content of the message seems to be different.  This should not be possible:
each message must be unique.

I<Error:> Folder $name is opened read-only

You can not write to this folder unless you have opened the folder to
write or append with L<new(access)|Mail::Box/"Constructors">, or the C<force> option is set true.

I<Error:> Folder $name not deleted: not writable.

The folder must be opened with write access via L<new(access)|Mail::Box/"Constructors">, otherwise
removing it will be refused.  So, you may have write-access according to
the operating system, but that will not automatically mean that this
C<delete> method permits you to.  The reverse remark is valid as well.

I<Error:> Invalid timespan '$timespan' specified.

The string does not follow the strict rules of the time span syntax which
is permitted as parameter.

I<Warning:> Message-id '$msgid' does not contain a domain.

According to the RFCs, message-ids need to contain a unique random part,
then an C<@>, and then a domain name.  This is made to avoid the creation
of two messages with the same id.  The warning emerges when the C<@> is
missing from the string.

I<Error:> Package $package does not implement $method.

Fatal error: the specific package (or one of its superclasses) does not
implement this method where it should. This message means that some other
related classes do implement this method however the class at hand does
not.  Probably you should investigate this and probably inform the author
of the package.

I<Error:> Unable to create subfolder $name of $folder.

The copy includes the subfolders, but for some reason it was not possible
to copy one of these.  Copying will proceed for all other sub-folders.

I<Error:> Unable to write message for $folder to $filename: $!

The new message could not be written to its new file, for the specific
reason.

I<Error:> Writing folder $name failed

For some reason (you probably got more error messages about this problem)
it is impossible to write the folder, although you should because there
were changes made.


=head1 DETAILS


=head2 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 L<Mail::Box::Thread::Manager|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 C<1>.  Next to these message files, a
directory may contain a file named C<.mh_sequences>, storing labels which
relate to the messages.  Furthermore, a folder-directory may contain
sub-directories, which are seen as sub-folders.

=head2 Labels

User actions on a message are flagged with a label.  When the folder is
opened, these flags are read from the C<.mh_sequences> file.  When the
folder is closed that file gets updated.  C<Status> and C<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.

=head2 This implementation

This implementation supports the C<.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 C<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.

L<Mail::Box::MH|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.

=head2 An index-file

If you specify L<new(keep_index)|"METHODS">, 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 C<.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.





=head1 REFERENCES

See the Mail::Box website at L<http://perl.overmeer.net/mailbox/> for more details.

=head1 COPYRIGHTS

Module version 2.042.
Written by Mark Overmeer (mark@overmeer.net).  See the ChangeLog for
other contributors.

Copyright (c) 2001-2003 by the author(s). All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.


