# SPDX-License-Identifier: GPL-2.0-or-later

package Amavis::MIME::Body::OnOpenFh;

# A body class that keeps data on an open file handle, read-only,
# while allowing to prepend a couple of lines when reading from it.
# $skip_bytes bytes at the beginning of a given open file are ignored.

use strict;
use re 'taint';

BEGIN {
  require Exporter;
  require MIME::Body;
  use vars qw(@ISA @EXPORT @EXPORT_OK %EXPORT_TAGS $VERSION);
  $VERSION = '2.412';
  @ISA = qw(Exporter MIME::Body);  # subclass of MIME::Body
}

use Amavis::Util qw(ll do_log);

sub init {
  my($self, $fh,$prefix_lines,$skip_bytes) = @_;
  $self->{MB_Am_fh} = $fh;
  $self->{MB_Am_prefix} = defined $prefix_lines ? join('',@$prefix_lines) : '';
  $self->{MB_Am_prefix_l} = length($self->{MB_Am_prefix});
  $self->{MB_Am_skip_bytes} = !defined $skip_bytes ? 0 : $skip_bytes;
  $self->is_encoded(1);
  $self;
}

sub open {
  my($self,$mode) = @_;
  $self->close;  # ignoring status
  $mode eq 'r' or die "Only offers read-only access, mode: $mode";
  my $fh = $self->{MB_Am_fh}; my $skip = $self->{MB_Am_skip_bytes};
  $fh->seek($skip,0) or die "Can't rewind mail file: $!";
  $self->{MB_Am_pos} = 0;
  bless { parent => $self };   #** One-argument "bless" warning
}

sub close { 1 }

sub read {  # SCALAR,LENGTH,OFFSET
  my $self = shift; my $len = $_[1]; my $offset = $_[2];
  my $parent = $self->{parent}; my $pos = $parent->{MB_Am_pos};
  my $str1 = ''; my $str2 = ''; my $nbytes = 0;
  if ($len > 0 && $pos < $parent->{MB_Am_prefix_l}) {
    $str1 = substr($parent->{MB_Am_prefix}, $pos, $len);
    $nbytes += length($str1); $len -= $nbytes;
  }
  my $msg;
  if ($len > 0) {
    my $nb = $parent->{MB_Am_fh}->read($str2,$len);
    if (!defined $nb) {
      $msg = "Error reading: $!";
    } elsif ($nb < 1) {
      # read returns 0 at eof
    } else {
      $nbytes += $nb; $len -= $nb;
    }
  }
  if (defined $msg) {
    undef $nbytes;  # $! already set by a failed read
  } else {
    ($offset ? substr($_[0],$offset) : $_[0]) = $str1.$str2;
    $pos += $nbytes; $parent->{MB_Am_pos} = $pos;
  }
  $nbytes;   # eof: 0;  error: undef
}

1;