=encoding utf8

=head1 NAME

Mail::Box::Parser - reading and writing messages

=head1 INHERITANCE

 Mail::Box::Parser
   is a Mail::Reporter

 Mail::Box::Parser is extended by
   Mail::Box::Parser::C
   Mail::Box::Parser::Perl

=head1 SYNOPSIS

 # Not instatiatiated itself

=head1 DESCRIPTION

The C<Mail::Box::Parser> manages the parsing of folders.  Usually, you won't
need to know anything about this module, except the options which are
involved with this code.

There are two implementations of this module planned:

=over 4

=item * L<Mail::Box::Parser::Perl|Mail::Box::Parser::Perl>

A slower parser which only uses plain Perl.  This module is a bit slower,
and does less checking and less recovery.

=item * L<Mail::Box::Parser::C|Mail::Box::Parser::C>

A fast parser written in C<C>.  This package is released as separate
module on CPAN, because the module distribution via CPAN can not
handle XS files which are not located in the root directory of the
module tree.  If a C compiler is available on your system, it will be
used automatically.

=back

Extends L<"DESCRIPTION" in Mail::Reporter|Mail::Reporter/"DESCRIPTION">.
 
=head1 METHODS

Extends L<"METHODS" in Mail::Reporter|Mail::Reporter/"METHODS">.
 
=head2 Constructors

Extends L<"Constructors" in Mail::Reporter|Mail::Reporter/"Constructors">.
 
=over 4

=item Mail::Box::Parser-E<gt>B<new>(%options)

Create a parser object which can handle one file.  For
mbox-like mailboxes, this object can be used to read a whole folder.  In
case of MH-like mailboxes, each message is contained in a single file,
so each message has its own parser object.

 -Option  --Defined in     --Default
  file                       undef
  filename                   <required>
  log       Mail::Reporter   'WARNINGS'
  mode                       'r'
  trace     Mail::Reporter   'WARNINGS'

=over 2

=item file => FILE-HANDLE

Any C<IO::File> or C<GLOB> which can be used to read the data from.  In
case this option is specified, the C<filename> is informational only.

=item filename => FILENAME

The name of the file to be read.

=item log => LEVEL

=item mode => OPENMODE

File-open mode, which defaults to C<'r'>, which means `read-only'.
See C<perldoc -f open> for possible modes.  Only applicable 
when no C<file> is specified.

=item trace => LEVEL

=back

=back

=head2 The parser

=over 4

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

Returns whether the file which is parsed has changed after the last
time takeFileInfo() was called.

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

Returns the name of the file this parser is working on.

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

Restart the parser on a certain file, usually because the content has
changed.

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

Start the parser by opening a file.

 -Option--Default
  file    undef

=over 2

=item file => FILEHANDLE|undef

The file is already open, for instance because the data must be read
from STDIN.

=back

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

Stop the parser, which will include a close of the file.  The lock on the
folder will not be removed (is not the responsibility of the parser).

=back

=head2 Parsing

=over 4

=item $obj-E<gt>B<bodyAsFile>( $fh [$chars, [$lines]] )

Try to read one message-body from the file, and immediately write
it to the specified file-handle.  Optionally, the predicted number
of CHARacterS and/or $lines to be read can be supplied.  These values may be
C<undef> and may be wrong.

The return is a list of three scalars: the location of the body (begin
and end) and the number of lines in the body.

=item $obj-E<gt>B<bodyAsList>( [$chars, [$lines]] )

Try to read one message-body from the file.  Optionally, the predicted number
of CHARacterS and/or $lines to be read can be supplied.  These values may be
C<undef> and may be wrong.

The return is a list of scalars, each containing one line (including
line terminator), preceded by two integers representing the location
in the file where this body started and ended.

=item $obj-E<gt>B<bodyAsString>( [$chars, [$lines]] )

Try to read one message-body from the file.  Optionally, the predicted number
of CHARacterS and/or $lines to be read can be supplied.  These values may be
C<undef> and may be wrong.

The return is a list of three scalars, the location in the file
where the body starts, where the body ends, and the string containing the
whole body.

=item $obj-E<gt>B<bodyDelayed>( [$chars, [$lines]] )

Try to read one message-body from the file, but the data is skipped.
Optionally, the predicted number of CHARacterS and/or $lines to be skipped
can be supplied.  These values may be C<undef> and may be wrong.

The return is a list of four scalars: the location of the body (begin and
end), the size of the body, and the number of lines in the body.  The
number of lines may be C<undef>.

=item $obj-E<gt>B<filePosition>( [$position] )

Returns the location of the next byte to be used in the file which is
parsed.  When a $position is specified, the location in the file is
moved to the indicated spot first.

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

Returns the character or characters which are used to separate lines
in the folder file.  This is based on the first line of the file.
UNIX systems use a single LF to separate lines.  Windows uses a CR and
a LF.  Mac uses CR.

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

Remove the last-pushed separator from the list which is maintained by the
parser.  This will return C<undef> when there is none left.

=item $obj-E<gt>B<pushSeparator>(STRING|Regexp)

Add a boundary line.  Separators tell the parser where to stop reading.
A famous separator is the C<From>-line, which is used in Mbox-like
folders to separate messages.  But also parts (I<attachments>) is a
message are divided by separators.

The specified STRING describes the start of the separator-line.  The
Regexp can specify a more complicated format.

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

Read the whole message-header and return it as list of field-value
pairs.  Mind that some fields will appear more than once.

The first element will represent the position in the file where the
header starts.  The follows the list of header field names and bodies.

example: 

 my ($where, @header) = $parser->readHeader;

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

Read the currently active separator (the last one which was pushed).  The
line (or C<undef>) is returned.  Blank-lines before the separator lines
are ignored.

The return are two scalars, where the first gives the location of the
separator in the file, and the second the line which is found as
separator.  A new separator is activated using L<pushSeparator()|Mail::Box::Parser/"Parsing">.

=back

=head2 Internals

=over 4

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

Close the file which was being parsed.

=item $obj-E<gt>B<defaultParserType>( [$class] )

=item Mail::Box::Parser-E<gt>B<defaultParserType>( [$class] )

Returns the parser to be used to parse all subsequent
messages, possibly first setting the parser using the optional argument.
Usually, the parser is autodetected; the C<C>-based parser will be used
when it can be, and the Perl-based parser will be used otherwise.

The $class argument allows you to specify a package name to force a
particular parser to be used (such as your own custom parser). You have
to C<use> or C<require> the package yourself before calling this method
with an argument. The parser must be a sub-class of C<Mail::Box::Parser>.

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

Open the file to be parsed.  $args is a ref-hash of options.

 -Option  --Default
  filename  <required>
  mode      <required>

=over 2

=item filename => FILENAME

=item mode => STRING

=back

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

Capture some data about the file being parsed, to be compared later.

=back

=head2 Error handling

Extends L<"Error handling" in Mail::Reporter|Mail::Reporter/"Error handling">.
 
=over 4

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

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

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

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

=item $obj-E<gt>B<defaultTrace>( [$level]|[$loglevel, $tracelevel]|[$level, $callback] )

=item Mail::Box::Parser-E<gt>B<defaultTrace>( [$level]|[$loglevel, $tracelevel]|[$level, $callback] )

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

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

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

=item $obj-E<gt>B<log>( [$level, [$strings]] )

=item Mail::Box::Parser-E<gt>B<log>( [$level, [$strings]] )

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

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

=item Mail::Box::Parser-E<gt>B<logPriority>($level)

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

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

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

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

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

=item $obj-E<gt>B<report>( [$level] )

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

=item $obj-E<gt>B<reportAll>( [$level] )

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

=item $obj-E<gt>B<trace>( [$level] )

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

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

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

=back

=head2 Cleanup

Extends L<"Cleanup" in Mail::Reporter|Mail::Reporter/"Cleanup">.
 
=over 4

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

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

=back

=head1 DIAGNOSTICS

=over 4

=item Warning: File $filename changed during access.

When a message parser starts working, it takes size and modification time
of the file at hand.  If the folder is written, it checks wether there
were changes in the file made by external programs.

Calling L<Mail::Box::update()|Mail::Box/"The folder"> on a folder before it being closed
will read these new messages.  But the real source of this problem is
locking: some external program (for instance the mail transfer agent,
like sendmail) uses a different locking mechanism as you do and therefore
violates your rights.

=item Error: Filename or handle required to create a parser.

A message parser needs to know the source of the message at creation.  These
sources can be a filename (string), file handle object or GLOB.
See new(filename) and new(file).

=item 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.

=back

=head1 SEE ALSO

This module is part of Mail-Message distribution version 3.004,
built on December 21, 2017.

Do not forget to read
L<Mail::Box-Overview>,
L<Mail::Box-Cookbook>, and
L<Mail::Box-Index>.
Examples are included in the Mail-Box distribution, directories 'examples'
and 'scripts'.

Browseable manuals, papers, and other released material van be found
at  Website: F<http://perl.overmeer.net/mailbox/>

The central modules (in separate distributions) in the MailBox suite are:
L<Mail::Message>,
L<Mail::Box>,
L<Mail::Box::IMAP4>,
L<Mail::Box::POP3>,
L<Mail::Box::Parser::C>,
L<Mail::Box::Dbx> (unpublished),
L<Mail::Transport>,
L<Object::Realize::Later>, and
L<User::Identity>.

Please post questions or ideas to the author F<markov@cpan.org>.

=head1 LICENSE

Copyrights 2001-2017 by [Mark Overmeer]. For other contributors see ChangeLog.

This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
See F<http://dev.perl.org/licenses/>

