=encoding utf8

=head1 NAME

Mail::Box::File - handle file-based folders

=head1 INHERITANCE

 Mail::Box::File
   is a Mail::Box
   is a Mail::Reporter

 Mail::Box::File is extended by
   Mail::Box::Mbox

=head1 SYNOPSIS

=head1 DESCRIPTION

C<Mail::Box::File> is the base-class for all file-based folders: folders
which bundle multiple messages into one single file.  Usually, these
messages are separated by a special line which indicates the start of
the next one.

Extends L<"DESCRIPTION" in Mail::Box|Mail::Box/"DESCRIPTION">.

=head1 OVERLOADED

Extends L<"OVERLOADED" in Mail::Box|Mail::Box/"OVERLOADED">.

=over 4

=item overload: B<'""'> stringification

Inherited, see L<Mail::Box/"OVERLOADED">

=item overload: B<'@{}'> use as ARRAY

Inherited, see L<Mail::Box/"OVERLOADED">

=item overload: B<cmp> string comparison

Inherited, see L<Mail::Box/"OVERLOADED">

=back

=head1 METHODS

Extends L<"METHODS" in Mail::Box|Mail::Box/"METHODS">.

=head2 Constructors

Extends L<"Constructors" in Mail::Box|Mail::Box/"Constructors">.

=over 4

=item $class-E<gt>B<new>(%options)

Inherited, see L<Mail::Box/"Constructors">

 -Option           --Defined in     --Default
  access             Mail::Box        'r'
  body_delayed_type  Mail::Box        Mail::Message::Body::Delayed
  body_type                           <see description>
  coerce_options     Mail::Box        +[]
  create             Mail::Box        false
  extract            Mail::Box        10240
  field_type         Mail::Box        undef
  fix_headers        Mail::Box        false
  folder             Mail::Box        $ENV{MAIL}
  folderdir          Mail::Box        $ENV{HOME}.'/Mail'
  head_delayed_type  Mail::Box        Mail::Message::Head::Delayed
  head_type          Mail::Box        Mail::Message::Head::Complete
  keep_dups          Mail::Box        false
  lock_extension                      '.lock'
  lock_file          Mail::Box        <foldername><lock-extension>
  lock_timeout       Mail::Box        1 hour
  lock_type          Mail::Box        Mail::Box::Locker::DotLock
  lock_wait          Mail::Box        10 seconds
  locker             Mail::Box        undef
  manager            Mail::Box        undef
  message_type       Mail::Box        Mail::Box::File::Message
  multipart_type     Mail::Box        Mail::Message::Body::Multipart
  remove_when_empty  Mail::Box        true
  save_on_exit       Mail::Box        true
  trusted            Mail::Box        <depends on folder location>
  write_policy                        undef

=over 2

=item access => $mode

=item body_delayed_type => CLASS

=item body_type => CLASS|CODE

The default C<body_type> option for C<File> folders, which will cause
messages larger than 10kB to be stored in files and smaller files
in memory, is implemented like this:

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

=item coerce_options => ARRAY

=item create => BOOLEAN

=item extract => INTEGER|CODE|METHOD|'LAZY'|'ALWAYS'

=item field_type => $class

=item fix_headers => BOOLEAN

=item folder => $name

=item folderdir => $directory

=item head_delayed_type => $class

=item head_type => $class

=item keep_dups => BOOLEAN

=item lock_extension => $file|STRING

When the dotlock locking mechanism is used, the lock is created with a
hardlink to the folder file.  For C<Mail::Box::File> type of folders, this
filename is by default named as the folder-file itself followed by
C<.lock>.  For example: the C<Mail/inbox> folder file will have a hardlink
made as C<Mail/inbox.lock>.

You may specify an absolute C<$file>, a relative (to the folder's
directory) filename, or an extension (preceded by a dot).  So valid
examples are:

  .lock                  # appended to the folder's filename
  my_own_lockfile.test   # full filename, same dir
  /etc/passwd            # somewhere else

When the program runs with less privileges (as normal user), often the
default inbox folder can not be locked with the lockfile name which is
produced by default.

=item lock_file => $file

=item lock_timeout => $seconds

=item lock_type => $class|$name|\@names

=item lock_wait => $seconds

=item locker => $locker

=item manager => $manager

=item message_type => $class

=item multipart_type => CLASS

=item remove_when_empty => BOOLEAN

=item save_on_exit => BOOLEAN

=item trusted => BOOLEAN

=item write_policy => 'REPLACE'|'INPLACE'|undef

Sets the default write policy, as default for a later call to
L<write(policy)|Mail::Box::File/"Internals">.  With C<undef>, the best policy is autodetected.

=back

=back

=head2 Attributes

Extends L<"Attributes" in Mail::Box|Mail::Box/"Attributes">.

=over 4

=item $obj-E<gt>B<filename>()

Returns the filename for this folder, which may be an absolute or relative
path to the file.

» example: 

  print $folder->filename;

=item $obj-E<gt>B<fixHeaders>()

Inherited, see L<Mail::Box/"Attributes">

=item $obj-E<gt>B<folderdir>( [$directory] )

Inherited, see L<Mail::Box/"Attributes">

=item $obj-E<gt>B<isTrusted>()

Inherited, see L<Mail::Box/"Attributes">

=item $obj-E<gt>B<name>()

Inherited, see L<Mail::Box/"Attributes">

=item $obj-E<gt>B<removeEmpty>()

Inherited, see L<Mail::Box/"Attributes">

=item $obj-E<gt>B<type>()

Inherited, see L<Mail::Box/"Attributes">

=back

=head2 The folder

Extends L<"The folder" in Mail::Box|Mail::Box/"The folder">.

=over 4

=item $obj-E<gt>B<addMessage>($message, %options)

Inherited, see L<Mail::Box/"The folder">

=item $obj-E<gt>B<addMessages>(@messages)

Inherited, see L<Mail::Box/"The folder">

=item $class-E<gt>B<appendMessages>(%options)

Appending messages to a file based folder which is not opened is a little
risky.  In practice, this is often done without locking the folder.  So,
another application may write to the folder at the same time... :(
Hopefully, all goes fast enough that the chance on collision is small.

All C<%options> of L<Mail::Box::Mbox::new()|Mail::Box::Mbox/"METHODS"> can be supplied.
Improves base, see L<Mail::Box/"The folder">

 -Option   --Defined in     --Default
  folder     Mail::Box        <required>
  lock_type                   NONE
  message    Mail::Box        undef
  messages   Mail::Box        undef
  share      Mail::Box        false

=over 2

=item folder => $name

=item lock_type => ...

See L<Mail::Box::new(lock_type)|Mail::Box/"Constructors"> for possible values.

=item message => $message

=item messages => $message|\@messages

=item share => BOOLEAN

=back

=item $obj-E<gt>B<close>(%options)

Inherited, see L<Mail::Box/"The folder">

=item $obj-E<gt>B<copyTo>($folder, %options)

Inherited, see L<Mail::Box/"The folder">

=item $obj-E<gt>B<delete>(%options)

Inherited, see L<Mail::Box/"The folder">

=item $obj-E<gt>B<organization>()

Inherited, see L<Mail::Box/"The folder">

=item $obj-E<gt>B<size>()

Inherited, see L<Mail::Box/"The folder">

=item $obj-E<gt>B<update>(%options)

Inherited, see L<Mail::Box/"The folder">

=item $obj-E<gt>B<url>()

Inherited, see L<Mail::Box/"The folder">

=back

=head2 Folder flags

Extends L<"Folder flags" in Mail::Box|Mail::Box/"Folder flags">.

=over 4

=item $obj-E<gt>B<access>()

Inherited, see L<Mail::Box/"Folder flags">

=item $obj-E<gt>B<isModified>()

Inherited, see L<Mail::Box/"Folder flags">

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

Inherited, see L<Mail::Box/"Folder flags">

=item $obj-E<gt>B<writable>()

Inherited, see L<Mail::Box/"Folder flags">

=back

=head2 The messages

Extends L<"The messages" in Mail::Box|Mail::Box/"The messages">.

=over 4

=item $obj-E<gt>B<current>( [$number|$message|$message_id] )

Inherited, see L<Mail::Box/"The messages">

=item $obj-E<gt>B<find>($message_id)

Inherited, see L<Mail::Box/"The messages">

=item $obj-E<gt>B<findFirstLabeled>( $label, [BOOLEAN, [\@msgs]] )

Inherited, see L<Mail::Box/"The messages">

=item $obj-E<gt>B<message>( $index, [$message] )

Inherited, see L<Mail::Box/"The messages">

=item $obj-E<gt>B<messageId>( $message_id, [$message] )

Inherited, see L<Mail::Box/"The messages">

=item $obj-E<gt>B<messageIds>()

Inherited, see L<Mail::Box/"The messages">

=item $obj-E<gt>B<messages>( <'ALL'|$range|'ACTIVE'|'DELETED'|$label| !$label|$filter> )

Inherited, see L<Mail::Box/"The messages">

=item $obj-E<gt>B<nrMessages>(%options)

Inherited, see L<Mail::Box/"The messages">

=item $obj-E<gt>B<scanForMessages>($message, $message_ids, $timespan, $window)

Inherited, see L<Mail::Box/"The messages">

=back

=head2 Sub-folders

Extends L<"Sub-folders" in Mail::Box|Mail::Box/"Sub-folders">.

=over 4

=item $any-E<gt>B<listSubFolders>(%options)

Inherited, see L<Mail::Box/"Sub-folders">

=item $any-E<gt>B<nameOfSubFolder>( $subname, [$parentname] )

Inherited, see L<Mail::Box/"Sub-folders">

=item $obj-E<gt>B<openRelatedFolder>(%options)

Inherited, see L<Mail::Box/"Sub-folders">

=item $obj-E<gt>B<openSubFolder>($subname, %options)

Inherited, see L<Mail::Box/"Sub-folders">

=item $any-E<gt>B<topFolderWithMessages>()

Inherited, see L<Mail::Box/"Sub-folders">

=back

=head2 Internals

Extends L<"Internals" in Mail::Box|Mail::Box/"Internals">.

=over 4

=item $obj-E<gt>B<coerce>($message, %options)

Inherited, see L<Mail::Box/"Internals">

=item $any-E<gt>B<create>($foldername, %options)

Inherited, see L<Mail::Box/"Internals">

 -Option   --Defined in--Default
  folderdir  Mail::Box   undef

=over 2

=item folderdir => $directory

=back

=item $obj-E<gt>B<determineBodyType>($message, $head)

Inherited, see L<Mail::Box/"Internals">

=item $any-E<gt>B<folderToFilename>( $foldername, $folderdir, [$subext] )

Translate a C<$foldername> into a filename, using the C<$folderdir> value
to replace a leading “C<<= >>”.  The optional C<$subext> is only used for MBOX
folders.

=item $class-E<gt>B<foundIn>( [$foldername], %options )

Inherited, see L<Mail::Box/"Internals">

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

Inherited, see L<Mail::Box/"Internals">

=item $obj-E<gt>B<locker>()

Inherited, see L<Mail::Box/"Internals">

=item $obj-E<gt>B<messageCreateOptions>( [$type, $config] )

Returns a key-value list of options to be used each time a new message
is read from a file.  The list is preceded by the C<$type> of message which
has to be created.

This data is used by L<readMessages()|Mail::Box/"Internals"> and L<updateMessages()|Mail::Box::File/"Internals">.  With
C<$type> and C<$config>, a new configuration is set.

=item $obj-E<gt>B<moveAwaySubFolder>($directory, $extension)

The C<$directory> is renamed by appending the C<$extension>, which defaults to “C<.d>”,
to make place for a folder file on that specific location.  C<false> is
returned if this failed.

=item $obj-E<gt>B<parser>()

Create a parser for this mailbox.  The parser stays alive as long as
the folder is open.

=item $obj-E<gt>B<read>(%options)

Inherited, see L<Mail::Box/"Internals">

=item $obj-E<gt>B<readMessages>(%options)

Inherited, see L<Mail::Box/"Internals">

=item $obj-E<gt>B<storeMessage>($message)

Inherited, see L<Mail::Box/"Internals">

=item $obj-E<gt>B<toBeThreaded>($messages)

Inherited, see L<Mail::Box/"Internals">

=item $obj-E<gt>B<toBeUnthreaded>($messages)

Inherited, see L<Mail::Box/"Internals">

=item $obj-E<gt>B<updateMessages>(%options)

For file based folders, the file handle stays open until the folder
is closed.  Update is therefore rather simple: move to the end
of the last known message, and continue reading...
Improves base, see L<Mail::Box/"Internals">

=item $obj-E<gt>B<write>(%options)

Inherited, see L<Mail::Box/"Internals">

 -Option      --Defined in     --Default
  force         Mail::Box        false
  policy                         undef
  save_deleted  Mail::Box        false

=over 2

=item force => BOOLEAN

=item policy => 'REPLACE'|'INPLACE'|undef

In what way will the mail folder be updated.  If not specified during the
write, the value of the L<new(write_policy)|Mail::Box::File/"METHODS"> at folder creation is taken.

Valid values:

=over 4

=item * C<REPLACE>

First a new folder is written in the same directory as the folder which has
to be updated, and then a call to move will throw away the old immediately
replacing it by the new.

Writing in C<REPLACE> module is slightly optimized: messages which are not
modified are copied from file to file, byte by byte.  This is much
faster than printing the data which is will be done for modified messages.

=item * C<INPLACE>

The original folder file will be opened read/write.  All message which where
not changed will be left untouched, until the first deleted or modified
message is detected.  All further messages are printed again.

=item * C<undef>

As default, or when C<undef> is explicitly specified, first C<REPLACE> mode
is tried.  Only when that fails, an C<INPLACE> update is performed.

=back

C<INPLACE> will be much faster than C<REPLACE> when applied on large
folders, however requires the C<truncate> function to be implemented on
your operating system (at least available for recent versions of Linux,
Solaris, Tru64, HPUX).  It is also dangerous: when the program is interrupted
during the update process, the folder is corrupted.  Data may be lost.

However, in some cases it is not possible to write the folder with
C<REPLACE>.  For instance, the usual incoming mail folder on UNIX is
stored in a directory where a user can not write.  Of course, the
C<root> and C<mail> users can, but if you want to use this Perl module
with permission of a normal user, you can only get it to work in C<INPLACE>
mode.  Be warned that in this case folder locking via a lockfile is not
possible as well.

=item save_deleted => BOOLEAN

=back

=item $obj-E<gt>B<writeMessages>(%options)

Inherited, see L<Mail::Box/"Internals">

=back

=head2 Other methods

Extends L<"Other methods" in Mail::Box|Mail::Box/"Other methods">.

=over 4

=item $any-E<gt>B<timespan2seconds>($time)

Inherited, see L<Mail::Box/"Other methods">

=back

=head2 Error handling

Extends L<"Error handling" in Mail::Box|Mail::Box/"Error handling">.

=over 4

=item $obj-E<gt>B<AUTOLOAD>()

Inherited, see L<Mail::Reporter/"Error handling">

=item $obj-E<gt>B<notImplemented>()

Inherited, see L<Mail::Reporter/"Error handling">

=back

=head2 Cleanup

Extends L<"Cleanup" in Mail::Box|Mail::Box/"Cleanup">.

=over 4

=item $obj-E<gt>B<DESTROY>()

Inherited, see L<Mail::Box/"Cleanup">

=back

=head1 DETAILS

Extends L<"DETAILS" in Mail::Box|Mail::Box/"DETAILS">.

=head2 Different kinds of folders

Extends L<"Different kinds of folders" in Mail::Box|Mail::Box/"Different kinds of folders">.

=head2 Available folder types

Extends L<"Available folder types" in Mail::Box|Mail::Box/"Available folder types">.

=head2 Folder class implementation

Extends L<"Folder class implementation" in Mail::Box|Mail::Box/"Folder class implementation">.

=head2 File based folders

File based folders maintain a folder (a set of messages) in one
single file.  The advantage is that your folder has only one
single name, which speeds-up access to all messages at once.

The disadvantage over directory based folder (see L<Mail::Box::Dir|Mail::Box::Dir>)
is that you have to construct some means to keep all message apart,
for instance by adding a message separator, and this will cause
problems.  Where access to all messages at once is faster in file
based folders, access to a single message is (much) slower, because
the whole folder must be read.

=head1 DIAGNOSTICS

=over 4

=item Error: cannot append messages to folder file $file: $!

Appending messages to a not-opened file-organized folder may fail when the
operating system does not allow write access to the file at hand.
Cast by C<appendMessages()>

=item Fault: cannot create directory $dir for folder $name: $!

While creating a file-organized folder, at most one level of directories
is created above it.  Apparently, more levels of directories are needed,
or the operating system does not allow you to create the directory.
Cast by C<create()>

=item Fault: cannot create folder file $file: $!

The file-organized folder file cannot be created for the indicated reason.
In common cases, the operating system does not grant you write access to
the directory where the folder file should be stored.
Cast by C<create()>

=item Error: cannot get a lock on $type folder $name.

Cast by C<new()>

=item Fault: cannot move away sub-folder $dir: $!

Cast by C<moveAwaySubFolder()>

=item Warning: cannot remove folder $name file $filename: $!

Writing an empty folder will usually cause that folder to be removed,
which fails for the indicated reason.  L<new(remove_when_empty)|Mail::Box/"Constructors">
controls whether the empty folder will removed; setting it to C<false>
(C<0>) may be needed to avoid this message.
Cast by C<write()>

=item Fault: cannot replace $to by $from to update folder $name: $!

The replace policy wrote a new folder file to update the existing, but
was unable to give the final touch: replacing the old version of the
folder file for the indicated reason.
Cast by C<write()>

=item Warning: changes not written to read-only folder $name.

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)|Mail::Box/"The folder"> if you want to overrule the access mode, or close
the folder with L<close(write)|Mail::Box/"The folder"> set to C<NEVER>.
Cast by C<close()>

=item Error: class $package does not implement method $method.

Fatal error: the specific C<$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.
Cast by C<notImplemented()>

=item Error: copying failed for one message.

For some reason, for instance disk full, removed by external process, or
read-protection, it is impossible to copy one of the messages.  Copying will
proceed for the other messages.
Cast by C<copyTo()>

=item 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 controlled by your operating system.
Cast by C<copyTo()>

=item 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.
Cast by C<messageId()>

=item Error: file $name too short to get write message $msgnr ($size < $expect)

L<Mail::Box|Mail::Box> is lazy: it tries to leave messages in the folders until they
are used, which saves time and memory usage.  When this message appears,
something is terribly wrong: some lazy message are needed for updating the
folder, but they cannot be retrieved from the original file anymore.  In
this case, messages can be lost.

This message does appear regularly on Windows systems when using the
'replace' write policy.  Please help to find the cause, probably something
to do with Windows incorrectly handling multiple filehandles open in the
same file.
Cast by C<write()>

=item Warning: folder $name file $file is write-protected.

The folder is opened writable or for appending via L<new(access)|Mail::Box/"Constructors">,
but the operating system does not permit writing to the C<$file>.  The folder
will be opened read-only.
Cast by C<new()>

=item Warning: 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.
Cast by C<delete()>

=item Error: folder file $name does not exist.

Cast by C<new()>

=item Error: invalid timespan '$span'.

The string does not follow the strict rules of the time span syntax which
is permitted as parameter.
Cast by C<timespan2seconds()>

=item 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.
Cast by C<messageId()>

=item Error: unable to update folder $name.

When a folder is to be written, both replace and inplace write policies are
tried,  If both fail, the whole update fails.  You may see other, related,
error messages to indicate the real problem.
Cast by C<write()>

=item Error: unknown value to folder->close(write => $when).

Cast by C<close()>

=item Error: you cannot add a message which is already part of a folder to a new one.  Please use moveTo or copyTo.

Cast by C<addMessage()>

=back

=head1 SEE ALSO

This module is part of Mail-Box version 4.02,
built on April 10, 2026. Website: F<http://perl.overmeer.net/CPAN/>

=head1 LICENSE

For contributors see file ChangeLog.

This software is copyright (c) 2001-2026 by Mark Overmeer.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

