#!/usr/bin/perl
#
# Script to retrieve a single article from a news server, either by
# message-id or by group name and article number.
#
# Usage:     nntpid <messageid>
#    or:     nntpid messageid               (angle brackets optional)
#    or:     nntpid news.group.name 1234    (group+number form)
#    or:     nntpid -a news.group.name      (download all available articles)
#
# The name of your news server is obtained from the environment variable
# NNTPSERVER, or from the file /etc/nntpserver if that's not set.
#
# This script supports AUTHINFO GENERIC authentication using the
# environment variable NNTPAUTH. It will only attempt this if it receives
# a 480 response from the news server; if your news server isn't paranoid
# then the script will never need to look at NNTPAUTH.

# Copyright 2000,2004 Simon Tatham. All rights reserved.

require 5.002;
use Socket;
use FileHandle;

$usage =
  "usage: nntpid [ -v ] [ -d ] <message-id>\n" .
  "   or: nntpid [ -v ] [ -d ] <newsgroup> <article-number>\n" .
  "   or: nntpid [ -v ] -a <newsgroup>\n" .
  "where: -v                  verbose (print interaction with news server)\n" .
  "       -d                  direct output (don't consider using PAGER)\n" .
  "       -a                  dump all articles in group to stdout as mbox\n" .
  " also: nntpid --version    report version number\n" .
  "       nntpid --help       display this help text\n" .
  "       nntpid --licence    display (MIT) licence text\n";

$licence =
  "nntpid is copyright 2000,2004 Simon Tatham.\n" .
  "\n" .
  "Permission is hereby granted, free of charge, to any person\n" .
  "obtaining a copy of this software and associated documentation files\n" .
  "(the \"Software\"), to deal in the Software without restriction,\n" .
  "including without limitation the rights to use, copy, modify, merge,\n" .
  "publish, distribute, sublicense, and/or sell copies of the Software,\n" .
  "and to permit persons to whom the Software is furnished to do so,\n" .
  "subject to the following conditions:\n" .
  "\n" .
  "The above copyright notice and this permission notice shall be\n" .
  "included in all copies or substantial portions of the Software.\n" .
  "\n" .
  "THE SOFTWARE IS PROVIDED \"AS IS\", WITHOUT WARRANTY OF ANY KIND,\n" .
  "EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF\n" .
  "MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND\n" .
  "NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS\n" .
  "BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN\n" .
  "ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN\n" .
  "CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE\n" .
  "SOFTWARE.\n";

$pager = 1;
$verbose = 0;
$all = 0;

while ($ARGV[0] =~ /^-(.+)$/) {
  shift @ARGV;
  $verbose = 1, next if $1 eq "v";
  $pager = 0, next if $1 eq "d";
  $all = 1, next if $1 eq "a";
  if ($1 eq "-help") {
    print STDERR $usage;
    exit 0;
  } elsif ($1 eq "-version") {
    if ('$Revision$' =~ /Revision:\s+(\d+)/) {
	print "nntpid revision $1\n";
    } else {
	print "nntpid: unknown revision\n";
    }
    exit 0;
  } elsif ($1 eq "-licence" or $1 eq "-license") {
    print $licence;
    exit 0;
  }
}

die $usage if !defined $ARGV[0];

if ($all) {
  $group = $ARGV[0];
} elsif (defined $ARGV[1]) {
  $group = $ARGV[0];
  $mid = $ARGV[1];
} else {
  $group = "misc.misc";
  $mid = $ARGV[0];
  $mid =~ s/^<//;
  $mid =~ s/>$//;
  $mid = "<$mid>";
}

$ns=$ENV{'NNTPSERVER'};
if (!defined $ns or !length $ns) {
  $ns = `cat /etc/nntpserver`;
  chomp $ns;
}
$port = (getservbyname("nntp", "tcp"))[2];
$ns = inet_aton($ns);
$proto = getprotobyname("tcp");
$paddr = sockaddr_in($port, $ns);

socket(S,PF_INET,SOCK_STREAM,$proto) or die "socket: $!";
connect(S,$paddr) or die "connect: $!";

S->autoflush(1);

$fatal = 1; # most errors need to be fatal

&getline;
$code =~ /^2\d\d/ or die "no initial greeting from server\n";

&docmd("MODE READER");
# some servers require a GROUP before an ARTICLE command
$numbers = &docmd("GROUP $group");
if ($all) {
    @numbers = split / /, $numbers;
    $fatal = 0; # ignore failure to retrieve any given article
    for ($mid = $numbers[1]; $mid <= $numbers[2]; $mid++) {
	$art = &getart($mid);
	$art =~ s/\n(>*From )/\n>$1/gs;
	print "From nntpid ".(localtime)."\n".$art."\n";
    }
} else {
    $art = &getart($mid);
    &docmd("QUIT");
    close S;

    if ($pager and -t STDOUT) {
	$pagername = $ENV{"PAGER"};
	$pagername = "more" unless defined $pagername;
	open PAGER, "| $pagername";
	print PAGER $art;
	close PAGER;
    } else {
	print $art;
    }
}

sub getart {
  my ($mid) = @_;
  $ret = &docmd("ARTICLE $mid");
  return undef if !defined $ret;
  $art = "";
  while (1) {
    &getline;
    s/[\r\n]//g;
    last if /^\.$/;
    s/^\.//;
    $art .= "$_\n";
  }
  return $art;
}

sub putline {
  my ($line) = @_;
  print STDERR ">>> $line\n" if $verbose;
  print S "$line\r\n";
}

sub getline {
  $_ = <S>;
  s/[\r\n]*$//s;
  $code = substr($_,0,3);
  print STDERR "<<< $_\n" if $verbose;
  return substr($_,4);
}

sub docmd {
  my ($cmd) = @_;
  # We go at most twice round the following loop. If the first attempt
  # to fetch the article fails with a 480 response, we try again
  # having authenticated first; but if the second attempt also fails
  # with 480, then the authentication didn't work, so we should give
  # up rather than try it pointlessly again.
  for my $n (0,1) {
    &putline($cmd);
    $line = &getline;
    if ($code eq "480") { &auth; } else { last; }
  }
  if ($code !~ /^2\d\d/) {
    die "failed on `$cmd':\n$_\n" if $fatal;
    return undef;
  }
  return $line;
}

sub auth {
  # Authentication.
  if ($ENV{"NNTPAUTH"}) {
    $auth = $ENV{"NNTPAUTH"};
    &putline("AUTHINFO GENERIC $auth");
    pipe AUTHSTDIN, TOAUTH or die "unable to create pipes";
    pipe FROMAUTH, AUTHSTDOUT or die "unable to create pipes";
    $pid = fork;
    if (!defined $pid) {
      die "unable to fork for authentication helper";
    } elsif ($pid == 0) {
      # we are child
      $ENV{"NNTP_AUTH_FDS"} = "0.1";
      open STDIN, "<&AUTHSTDIN";
      open STDOUT, ">&AUTHSTDOUT";
      close S;
      exec $auth;
    }
    # we are parent
    close AUTHSTDIN;
    close AUTHSTDOUT;
    autoflush TOAUTH 1;
    &getline; print TOAUTH "$_\n";
    while (<FROMAUTH>) {
      s/[\r\n]*$//s;
      &putline($_);
      &getline;
      print TOAUTH "$_\n";
    }
    die "failed authentication\n" unless $? == 0;
  }
}