Net::libnetFAQ (3)
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NAME
libnetFAQ - libnet Frequently Asked QuestionsDESCRIPTION
Where to get this document
This document is distributed with the libnet distribution, and is also available on the libnet web page at
search.cpan.org/dist/libnet
How to contribute to this document
You may report corrections, additions, and suggestions on the
rt.cpan.org/Public/Bug/Report.html?Queue=libnet
Author and Copyright Information
Copyright (c) 1997-1998 Graham Barr. All rights reserved. This document is free; you can redistribute it and/or modify it under the terms of the Artistic License.Currently maintained by Steve Hay <shay@cpan.org>.
Disclaimer
This information is offered in good faith and in the hope that it may be of use, but is not guaranteed to be correct, up to date, or suitable for any particular purpose whatsoever. The authors accept no liability in respect of this information or its use.Obtaining and installing libnet
What is libnet ?
libnet is a collection of perl5 modules which all related to network programming. The majority of the modules available provided the client side of popular server-client protocols that are used in the internet community.Which version of perl do I need ?
This version of libnet requires Perl 5.8.1 or higher.What other modules do I need ?
No non-core modules are required for normal use, except on os390, which requires Convert::EBCDIC.Authen::SASL is required for
IO::Socket::SSL version 2.007 or higher is required for
IO::Socket::IP version 0.20 or IO::Socket::INET6 version 2.62 is required for IPv6 support.
What machines support libnet ?
libnet itself is an entirely perl-code distribution so it should work on any machine that perl runs on.Where can I get the latest libnet release
The latest libnet release is always on
search.cpan.org/dist/libnet
Using Net::FTP
How do I download files from an FTP server ?
An example taken from an article posted to comp.lang.perl.misc
#!/your/path/to/perl
# a module making life easier
use Net::FTP;
# for debugging: $ftp = Net::FTP->new('site','Debug',10);
# open a connection and log in!
$ftp = Net::FTP->new('target_site.somewhere.xxx');
$ftp->login('username','password');
# set transfer mode to binary
$ftp->binary();
# change the directory on the ftp site
$ftp->cwd('/some/path/to/somewhere/');
foreach $name ('file1', 'file2', 'file3') {
# get's arguments are in the following order:
# ftp server's filename
# filename to save the transfer to on the local machine
# can be simply used as get($name) if you want the same name
$ftp->get($name,$name);
}
# ftp done!
$ftp->quit;
How do I transfer files in binary mode ?
To transfer files without <
$ftp->binary;
How can I get the size of a file on a remote FTP server ?
How can I get the modification time of a file on a remote FTP server ?
How can I change the permissions of a file on a remote server ?
The
$ftp->quot('site chmod 0777',$filename);
But this is not guaranteed to work.
Can I do a reget operation like the ftp command ?
How do I get a directory listing from an FTP server ?
Changing directory to does not fail ?
Passing an argument of "" to ->cwd() has the same affect of calling ->cwd() without any arguments. Turn on Debug (See below) and you will see what is happening
$ftp = Net::FTP->new($host, Debug => 1);
$ftp->login;
$ftp->cwd("");
gives
Net::FTP=GLOB(0x82196d8)>>> CWD /
Net::FTP=GLOB(0x82196d8)<<< 250 CWD command successful.
I am behind a SOCKS firewall, but the Firewall option does not work ?
The Firewall option is only for support of one type of firewall. The type
supported is an ftp proxy.
To use Net::FTP, or any other module in the libnet distribution, through a
I am behind an FTP proxy firewall, but cannot access machines outside ?
Net::FTP implements the most popular ftp proxy firewall approach. The scheme
implemented is that where you log in to the firewall with "user@hostname"
I have heard of one other type of firewall which requires a login to the firewall with an account, then a second login with "user@hostname". You can still use Net::FTP to traverse these firewalls, but a more manual approach must be taken, eg
$ftp = Net::FTP->new($firewall) or die $@;
$ftp->login($firewall_user, $firewall_passwd) or die $ftp->message;
$ftp->login($ext_user . '@' . $ext_host, $ext_passwd) or die $ftp->message.
My ftp proxy firewall does not listen on port 21
If you pass a port number to Net::FTP then it assumes this is the port number of the final destination. By default Net::FTP will always try to connect to the firewall on port 21.
Net::FTP uses IO::Socket to open the connection and IO::Socket allows the port number to be specified as part of the hostname. So this problem can be resolved by either passing a Firewall option like "hostname:1234" or by setting the "ftp_firewall" option in Net::Config to be a string in the same form.
Is it possible to change the file permissions of a file on an FTP server ?
The answer to this is ``maybe''. The
$ftp->site('chmod','0775',$file);
I have seen scripts call a method message, but cannot find it documented ?
Net::FTP, like several other packages in libnet, inherits from Net::Cmd, so all the methods described in Net::Cmd are also available on Net::FTP objects.Why does Net::FTP not implement mput and mget methods
The quick answer is because they are easy to implement yourself. The long answer is that to write these in such a way that multiple platforms are supported correctly would just require too much code. Below are some examples how you can implement these yourself.
sub mput {
my($ftp,$pattern) = @_;
foreach my $file (glob($pattern)) {
$ftp->put($file) or warn $ftp->message;
}
}
sub mget {
my($ftp,$pattern) = @_;
foreach my $file ($ftp->ls($pattern)) {
$ftp->get($file) or warn $ftp->message;
}
}
Using Net::SMTP
Why can't the part of an Email address after the @ be used as the hostname ?
The part of an Email address which follows the @ is not necessarily a hostname, it is a mail domain. To find the name of a host to connect for a mail domain you need to do aWhy does Net::SMTP not do DNS MX lookups ?
Net::SMTP implements the The verify method always returns true ?
Well it may seem that way, but it does not. The verify method returns true if the command succeeded. If you pass verify an address which the server would normally have to forward to another machine, the command will succeed with something like
252 Couldn't verify <someone@there> but will attempt delivery anyway
This command will fail only if you pass it an address in a domain the server directly delivers for, and that address does not exist.
Debugging scripts
How can I debug my scripts that use Net::* modules ?
Most of the libnet client classes allow options to be passed to the constructor, in most cases one option is called "Debug". Passing this option with a non-zero value will turn on a protocol trace, which will be sent to
#!/your/path/to/perl
use Net::FTP;
my $ftp = new Net::FTP($host, Debug => 1);
$ftp->login('gbarr','password');
$ftp->quit;
this script would output something like
Net::FTP: Net::FTP(2.22) Net::FTP: Exporter Net::FTP: Net::Cmd(2.0801) Net::FTP: IO::Socket::INET Net::FTP: IO::Socket(1.1603) Net::FTP: IO::Handle(1.1504) Net::FTP=GLOB(0x8152974)<<< 220 imagine FTP server (Version wu-2.4(5) Tue Jul 29 11:17:18 CDT 1997) ready. Net::FTP=GLOB(0x8152974)>>> user gbarr Net::FTP=GLOB(0x8152974)<<< 331 Password required for gbarr. Net::FTP=GLOB(0x8152974)>>> PASS .... Net::FTP=GLOB(0x8152974)<<< 230 User gbarr logged in. Access restrictions apply. Net::FTP=GLOB(0x8152974)>>> QUIT Net::FTP=GLOB(0x8152974)<<< 221 Goodbye.
The first few lines tell you the modules that Net::FTP uses and their versions, this is useful data to me when a user reports a bug. The last seven lines show the communication with the server. Each line has three parts. The first part is the object itself, this is useful for separating the output if you are using multiple objects. The second part is either "<<<<" to show data coming from the server or ">>>>" to show data going to the server. The remainder of the line is the command being sent or response being received.