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local/lib/perl5/IO/Async/FileStream.pm  view on Meta::CPAN

Because this is a subclass of L<IO::Async::Stream> in read-only mode, all the
events supported by C<Stream> relating to the read handle are supported here.
This is not a full list; see also the documentation relating to
L<IO::Async::Stream>.

=head2 $ret = on_read \$buffer, $eof

Invoked when more data is available in the internal receiving buffer.

Note that C<$eof> only indicates that all the data currently available in the
file has now been read; in contrast to a regular L<IO::Async::Stream>, this
object will not stop watching after this condition. Instead, it will continue
watching the file for updates.

=head2 on_truncated

Invoked when the file size shrinks. If this happens, it is presumed that the
file content has been replaced. Reading will then commence from the start of
the file.

=head2 on_initial $size

Invoked the first time the file is looked at. It is passed the initial size of
the file. The code implementing this method can use the C<seek> or
C<seek_to_last> methods to set the initial read position in the file to skip
over some initial content.

This method may be useful to skip initial content in the file, if the object
should only respond to new content added after it was created.

=cut

sub _init
{
   my $self = shift;
   my ( $params ) = @_;

   $self->SUPER::_init( $params );

   $params->{close_on_read_eof} = 0;

   $self->{last_size} = undef;

   $self->add_child( $self->{file} = IO::Async::File->new(
      on_devino_changed => $self->_replace_weakself( 'on_devino_changed' ),
      on_size_changed   => $self->_replace_weakself( 'on_size_changed' ),
   ) );
}

=head1 PARAMETERS

The following named parameters may be passed to C<new> or C<configure>, in
addition to the parameters relating to reading supported by
L<IO::Async::Stream>.

=head2 filename => STRING

Optional. If supplied, watches the named file rather than the filehandle given
in C<read_handle>. The file will be opened by the constructor, and then
watched for renames. If the file is renamed, the new filename is opened and
tracked similarly after closing the previous file.

=head2 interval => NUM

Optional. The interval in seconds to poll the filehandle using C<stat(2)>
looking for size changes. A default of 2 seconds will be applied if not
defined.

=cut

sub configure
{
   my $self = shift;
   my %params = @_;

   foreach (qw( on_truncated on_initial )) {
      $self->{$_} = delete $params{$_} if exists $params{$_};
   }

   foreach (qw( interval )) {
      $self->{file}->configure( $_ => delete $params{$_} ) if exists $params{$_};
   }
   if( exists $params{filename} ) {
      $self->{file}->configure( filename => delete $params{filename} );
      $params{read_handle} = $self->{file}->handle;
   }
   elsif( exists $params{handle} or exists $params{read_handle} ) {
      my $handle = delete $params{handle};
      defined $handle or $handle = delete $params{read_handle};

      $self->{file}->configure( handle => $handle );
      $params{read_handle} = $self->{file}->handle;
   }

   croak "Cannot have a write_handle in a ".ref($self) if defined $params{write_handle};

   $self->SUPER::configure( %params );

   if( $self->read_handle and !defined $self->{last_size} ) {
      my $size = (stat $self->read_handle)[7];

      $self->{last_size} = $size;

      local $self->{running_initial} = 1;
      $self->maybe_invoke_event( on_initial => $size );
   }
}

=head1 METHODS

=cut

# Replace IO::Async::Handle's implementation
sub _watch_read
{
   my $self = shift;
   my ( $want ) = @_;

   if( $want ) {
      $self->{file}->start if !$self->{file}->is_running;
   }
   else {
      $self->{file}->stop;
   }
}

sub _watch_write
{
   my $self = shift;
   my ( $want ) = @_;

   croak "Cannot _watch_write in " . ref($self) if $want;
}

sub on_devino_changed
{
   my $self = shift or return;

   $self->{renamed} = 1;
   $self->debug_printf( "read tail of old file" );
   $self->read_more;
}

sub on_size_changed
{
   my $self = shift or return;
   my ( $size ) = @_;

   if( $size < $self->{last_size} ) {
      $self->maybe_invoke_event( on_truncated => );
      $self->{last_pos} = 0;
   }

   $self->{last_size} = $size;

   $self->debug_printf( "read_more" );
   $self->read_more;
}

sub read_more
{
   my $self = shift;

   sysseek( $self->read_handle, $self->{last_pos}, SEEK_SET ) if defined $self->{last_pos};

   $self->on_read_ready;

   $self->{last_pos} = sysseek( $self->read_handle, 0, SEEK_CUR ); # == systell

   if( $self->{last_pos} < $self->{last_size} ) {
      $self->loop->later( sub { $self->read_more } );
   }
   elsif( $self->{renamed} ) {
      $self->debug_printf( "reopening for rename" );

      $self->{last_size} = 0;

      if( $self->{last_pos} ) {
         $self->maybe_invoke_event( on_truncated => );
         $self->{last_pos} = 0;
         $self->loop->later( sub { $self->read_more } );
      }

      $self->configure( read_handle => $self->{file}->handle );
      undef $self->{renamed};
   }
}

sub write
{
   carp "Cannot ->write from a ".ref($_[0]);
}

=head2 seek

   $filestream->seek( $offset, $whence )

Callable only during the C<on_initial> event. Moves the read position in the
filehandle to the given offset. C<$whence> is interpreted as for C<sysseek>,
should be either C<SEEK_SET>, C<SEEK_CUR> or C<SEEK_END>. Will be set to
C<SEEK_SET> if not provided.

Normally this would be used to seek to the end of the file, for example

 on_initial => sub {
    my ( $self, $filesize ) = @_;
    $self->seek( $filesize );
 }

=cut

sub seek
{
   my $self = shift;
   my ( $offset, $whence ) = @_;

   $self->{running_initial} or croak "Cannot ->seek except during on_initial";

   defined $whence or $whence = SEEK_SET;

   sysseek( $self->read_handle, $offset, $whence );
}

=head2 seek_to_last

   $success = $filestream->seek_to_last( $str_pattern, %opts )

Callable only during the C<on_initial> event. Attempts to move the read
position in the filehandle to just after the last occurance of a given match.
C<$str_pattern> may be a literal string or regexp pattern. 

Returns a true value if the seek was successful, or false if not. Takes the
following named arguments:

=over 8

=item blocksize => INT

Optional. Read the file in blocks of this size. Will take a default of 8KiB if
not defined.

=item horizon => INT

Optional. Give up looking for a match after this number of bytes. Will take a
default value of 4 times the blocksize if not defined.