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   1  =head1 NAME
   2  
   3  libnetFAQ - libnet Frequently Asked Questions
   4  
   5  =head1 DESCRIPTION
   6  
   7  =head2 Where to get this document
   8  
   9  This document is distributed with the libnet distribution, and is also
  10  available on the libnet web page at
  11  
  12      http://search.cpan.org/~gbarr/libnet/
  13  
  14  =head2 How to contribute to this document
  15  
  16  You may mail corrections, additions, and suggestions to me
  17  gbarr@pobox.com.
  18  
  19  =head1 Author and Copyright Information
  20  
  21  Copyright (c) 1997-1998 Graham Barr. All rights reserved.
  22  This document is free; you can redistribute it and/or modify it
  23  under the terms of the Artistic License.
  24  
  25  =head2 Disclaimer
  26  
  27  This information is offered in good faith and in the hope that it may
  28  be of use, but is not guaranteed to be correct, up to date, or suitable
  29  for any particular purpose whatsoever.  The authors accept no liability
  30  in respect of this information or its use.
  31  
  32  
  33  =head1 Obtaining and installing libnet
  34  
  35  =head2 What is libnet ?
  36  
  37  libnet is a collection of perl5 modules which all related to network
  38  programming. The majority of the modules available provided the
  39  client side of popular server-client protocols that are used in
  40  the internet community.
  41  
  42  =head2 Which version of perl do I need ?
  43  
  44  libnet has been know to work with versions of perl from 5.002 onwards. However
  45  if your release of perl is prior to perl5.004 then you will need to
  46  obtain and install the IO distribution from CPAN. If you have perl5.004
  47  or later then you will have the IO modules in your installation already,
  48  but CPAN may contain updates.
  49  
  50  =head2 What other modules do I need ?
  51  
  52  The only modules you will need installed are the modules from the IO
  53  distribution. If you have perl5.004 or later you will already have
  54  these modules.
  55  
  56  =head2 What machines support libnet ?
  57  
  58  libnet itself is an entirely perl-code distribution so it should work
  59  on any machine that perl runs on. However IO may not work
  60  with some machines and earlier releases of perl. But this
  61  should not be the case with perl version 5.004 or later.
  62  
  63  =head2 Where can I get the latest libnet release
  64  
  65  The latest libnet release is always on CPAN, you will find it
  66  in 
  67  
  68   http://www.cpan.org/modules/by-module/Net/
  69  
  70  The latest release and information is also available on the libnet web page
  71  at
  72  
  73   http://search.cpan.org/~gbarr/libnet/
  74  
  75  =head1 Using Net::FTP
  76  
  77  =head2 How do I download files from an FTP server ?
  78  
  79  An example taken from an article posted to comp.lang.perl.misc
  80  
  81      #!/your/path/to/perl
  82  
  83      # a module making life easier
  84  
  85      use Net::FTP;
  86  
  87      # for debugging: $ftp = Net::FTP->new('site','Debug',10);
  88      # open a connection and log in!
  89  
  90      $ftp = Net::FTP->new('target_site.somewhere.xxx');
  91      $ftp->login('username','password');
  92  
  93      # set transfer mode to binary
  94  
  95      $ftp->binary();
  96  
  97      # change the directory on the ftp site
  98  
  99      $ftp->cwd('/some/path/to/somewhere/');
 100  
 101      foreach $name ('file1', 'file2', 'file3') {
 102  
 103      # get's arguments are in the following order:
 104      # ftp server's filename
 105      # filename to save the transfer to on the local machine
 106      # can be simply used as get($name) if you want the same name
 107  
 108        $ftp->get($name,$name);
 109      }
 110  
 111      # ftp done!
 112  
 113      $ftp->quit;
 114  
 115  =head2 How do I transfer files in binary mode ?
 116  
 117  To transfer files without <LF><CR> translation Net::FTP provides
 118  the C<binary> method
 119  
 120      $ftp->binary;
 121  
 122  =head2 How can I get the size of a file on a remote FTP server ?
 123  
 124  =head2 How can I get the modification time of a file on a remote FTP server ?
 125  
 126  =head2 How can I change the permissions of a file on a remote server ?
 127  
 128  The FTP protocol does not have a command for changing the permissions
 129  of a file on the remote server. But some ftp servers may allow a chmod
 130  command to be issued via a SITE command, eg
 131  
 132      $ftp->quot('site chmod 0777',$filename);
 133  
 134  But this is not guaranteed to work.
 135  
 136  =head2 Can I do a reget operation like the ftp command ?
 137  
 138  =head2 How do I get a directory listing from an FTP server ?
 139  
 140  =head2 Changing directory to "" does not fail ?
 141  
 142  Passing an argument of "" to ->cwd() has the same affect of calling ->cwd()
 143  without any arguments. Turn on Debug (I<See below>) and you will see what is
 144  happening
 145  
 146      $ftp = Net::FTP->new($host, Debug => 1);
 147      $ftp->login;
 148      $ftp->cwd("");
 149  
 150  gives
 151  
 152      Net::FTP=GLOB(0x82196d8)>>> CWD /
 153      Net::FTP=GLOB(0x82196d8)<<< 250 CWD command successful.
 154  
 155  =head2 I am behind a SOCKS firewall, but the Firewall option does not work ?
 156  
 157  The Firewall option is only for support of one type of firewall. The type
 158  supported is an ftp proxy.
 159  
 160  To use Net::FTP, or any other module in the libnet distribution,
 161  through a SOCKS firewall you must create a socks-ified perl executable
 162  by compiling perl with the socks library.
 163  
 164  =head2 I am behind an FTP proxy firewall, but cannot access machines outside ?
 165  
 166  Net::FTP implements the most popular ftp proxy firewall approach. The scheme
 167  implemented is that where you log in to the firewall with C<user@hostname>
 168  
 169  I have heard of one other type of firewall which requires a login to the
 170  firewall with an account, then a second login with C<user@hostname>. You can
 171  still use Net::FTP to traverse these firewalls, but a more manual approach
 172  must be taken, eg
 173  
 174      $ftp = Net::FTP->new($firewall) or die $@;
 175      $ftp->login($firewall_user, $firewall_passwd) or die $ftp->message;
 176      $ftp->login($ext_user . '@' . $ext_host, $ext_passwd) or die $ftp->message.
 177  
 178  =head2 My ftp proxy firewall does not listen on port 21
 179  
 180  FTP servers usually listen on the same port number, port 21, as any other
 181  FTP server. But there is no reason why this has to be the case.
 182  
 183  If you pass a port number to Net::FTP then it assumes this is the port
 184  number of the final destination. By default Net::FTP will always try
 185  to connect to the firewall on port 21.
 186  
 187  Net::FTP uses IO::Socket to open the connection and IO::Socket allows
 188  the port number to be specified as part of the hostname. So this problem
 189  can be resolved by either passing a Firewall option like C<"hostname:1234">
 190  or by setting the C<ftp_firewall> option in Net::Config to be a string
 191  in in the same form.
 192  
 193  =head2 Is it possible to change the file permissions of a file on an FTP server ?
 194  
 195  The answer to this is "maybe". The FTP protocol does not specify a command to change
 196  file permissions on a remote host. However many servers do allow you to run the
 197  chmod command via the C<SITE> command. This can be done with
 198  
 199    $ftp->site('chmod','0775',$file);
 200  
 201  =head2 I have seen scripts call a method message, but cannot find it documented ?
 202  
 203  Net::FTP, like several other packages in libnet, inherits from Net::Cmd, so
 204  all the methods described in Net::Cmd are also available on Net::FTP
 205  objects.
 206  
 207  =head2 Why does Net::FTP not implement mput and mget methods
 208  
 209  The quick answer is because they are easy to implement yourself. The long
 210  answer is that to write these in such a way that multiple platforms are
 211  supported correctly would just require too much code. Below are
 212  some examples how you can implement these yourself.
 213  
 214  sub mput {
 215    my($ftp,$pattern) = @_;
 216    foreach my $file (glob($pattern)) {
 217      $ftp->put($file) or warn $ftp->message;
 218    }
 219  }
 220  
 221  sub mget {
 222    my($ftp,$pattern) = @_;
 223    foreach my $file ($ftp->ls($pattern)) {
 224      $ftp->get($file) or warn $ftp->message;
 225    }
 226  }
 227  
 228  
 229  =head1 Using Net::SMTP
 230  
 231  =head2 Why can't the part of an Email address after the @ be used as the hostname ?
 232  
 233  The part of an Email address which follows the @ is not necessarily a hostname,
 234  it is a mail domain. To find the name of a host to connect for a mail domain
 235  you need to do a DNS MX lookup
 236  
 237  =head2 Why does Net::SMTP not do DNS MX lookups ?
 238  
 239  Net::SMTP implements the SMTP protocol. The DNS MX lookup is not part
 240  of this protocol.
 241  
 242  =head2 The verify method always returns true ?
 243  
 244  Well it may seem that way, but it does not. The verify method returns true
 245  if the command succeeded. If you pass verify an address which the
 246  server would normally have to forward to another machine, the command
 247  will succeed with something like
 248  
 249      252 Couldn't verify <someone@there> but will attempt delivery anyway
 250  
 251  This command will fail only if you pass it an address in a domain
 252  the server directly delivers for, and that address does not exist.
 253  
 254  =head1 Debugging scripts
 255  
 256  =head2 How can I debug my scripts that use Net::* modules ?
 257  
 258  Most of the libnet client classes allow options to be passed to the
 259  constructor, in most cases one option is called C<Debug>. Passing
 260  this option with a non-zero value will turn on a protocol trace, which
 261  will be sent to STDERR. This trace can be useful to see what commands
 262  are being sent to the remote server and what responses are being
 263  received back.
 264  
 265      #!/your/path/to/perl
 266  
 267      use Net::FTP;
 268  
 269      my $ftp = new Net::FTP($host, Debug => 1);
 270      $ftp->login('gbarr','password');
 271      $ftp->quit;
 272  
 273  this script would output something like
 274  
 275   Net::FTP: Net::FTP(2.22)
 276   Net::FTP:   Exporter
 277   Net::FTP:   Net::Cmd(2.0801)
 278   Net::FTP:   IO::Socket::INET
 279   Net::FTP:     IO::Socket(1.1603)
 280   Net::FTP:       IO::Handle(1.1504)
 281  
 282   Net::FTP=GLOB(0x8152974)<<< 220 imagine FTP server (Version wu-2.4(5) Tue Jul 29 11:17:18 CDT 1997) ready.
 283   Net::FTP=GLOB(0x8152974)>>> user gbarr
 284   Net::FTP=GLOB(0x8152974)<<< 331 Password required for gbarr.
 285   Net::FTP=GLOB(0x8152974)>>> PASS ....
 286   Net::FTP=GLOB(0x8152974)<<< 230 User gbarr logged in.  Access restrictions apply.
 287   Net::FTP=GLOB(0x8152974)>>> QUIT
 288   Net::FTP=GLOB(0x8152974)<<< 221 Goodbye.
 289  
 290  The first few lines tell you the modules that Net::FTP uses and their versions,
 291  this is useful data to me when a user reports a bug. The last seven lines
 292  show the communication with the server. Each line has three parts. The first
 293  part is the object itself, this is useful for separating the output
 294  if you are using multiple objects. The second part is either C<<<<<> to
 295  show data coming from the server or C<&gt&gt&gt&gt> to show data
 296  going to the server. The remainder of the line is the command
 297  being sent or response being received.
 298  
 299  =head1 AUTHOR AND COPYRIGHT
 300  
 301  Copyright (c) 1997 Graham Barr.
 302  All rights reserved.
 303