Net::libnetFAQ(3p) Perl Programmers Reference Guide Net::libnetFAQ(3p) #
Net::libnetFAQ(3p) Perl Programmers Reference Guide Net::libnetFAQ(3p)
NNAAMMEE #
libnetFAQ - libnet Frequently Asked Questions
DDEESSCCRRIIPPTTIIOONN #
WWhheerree ttoo ggeett tthhiiss ddooccuummeenntt This document is distributed with the libnet distribution, and is also available on the libnet web page at
<https://metacpan.org/release/libnet>
HHooww ttoo ccoonnttrriibbuuttee ttoo tthhiiss ddooccuummeenntt You may report corrections, additions, and suggestions on the CPAN Request Tracker at
<https://rt.cpan.org/Public/Bug/Report.html?Queue=libnet>
AAuutthhoorr aanndd CCooppyyrriigghhtt IInnffoorrmmaattiioonn Copyright (C) 1997-1998 Graham Barr. All rights reserved. This document is free; you can redistribute it and/or modify it under the same terms as Perl itself, i.e. under the terms of either the GNU General Public License or the Artistic License, as specified in the _L_I_C_E_N_C_E file.
Steve Hay <shay@cpan.org <mailto:shay@cpan.org>> is now maintaining
libnet as of version 1.22_02.
DDiissccllaaiimmeerr 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.
OObbttaaiinniinngg aanndd iinnssttaalllliinngg lliibbnneett WWhhaatt iiss lliibbnneett ?? 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.
WWhhiicchh vveerrssiioonn ooff ppeerrll ddoo II nneeeedd ?? This version of libnet requires Perl 5.8.1 or higher.
WWhhaatt ootthheerr mmoodduulleess ddoo II nneeeedd ?? No non-core modules are required for normal use, except on os390, which requires Convert::EBCDIC.
Authen::SASL is required for AUTH support.
IO::Socket::SSL version 2.007 or higher is required for SSL support.
IO::Socket::IP version 0.25 or IO::Socket::INET6 version 2.62 is required
for IPv6 support.
WWhhaatt mmaacchhiinneess ssuuppppoorrtt lliibbnneett ?? libnet itself is an entirely perl-code distribution so it should work on any machine that perl runs on.
WWhheerree ccaann II ggeett tthhee llaatteesstt lliibbnneett rreelleeaassee The latest libnet release is always on CPAN, you will find it in
<https://metacpan.org/release/libnet>
UUssiinngg NNeett::::FFTTPP HHooww ddoo II ddoowwnnllooaadd ffiilleess ffrroomm aann FFTTPP sseerrvveerr ?? 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;
HHooww ddoo II ttrraannssffeerr ffiilleess iinn bbiinnaarryy mmooddee ??
To transfer files without
$ftp->binary;
HHooww ccaann II ggeett tthhee ssiizzee ooff aa ffiillee oonn aa rreemmoottee FFTTPP sseerrvveerr ?? HHooww ccaann II ggeett tthhee mmooddiiffiiccaattiioonn ttiimmee ooff aa ffiillee oonn aa rreemmoottee FFTTPP sseerrvveerr ?? HHooww ccaann II cchhaannggee tthhee ppeerrmmiissssiioonnss ooff aa ffiillee oonn aa rreemmoottee sseerrvveerr ?? The FTP protocol does not have a command for changing the permissions of a file on the remote server. But some ftp servers may allow a chmod command to be issued via a SITE command, eg
$ftp->quot('site chmod 0777',$filename);
But this is not guaranteed to work.
CCaann II ddoo aa rreeggeett ooppeerraattiioonn lliikkee tthhee ffttpp ccoommmmaanndd ?? HHooww ddoo II ggeett aa ddiirreeccttoorryy lliissttiinngg ffrroomm aann FFTTPP sseerrvveerr ?? CChhaannggiinngg ddiirreeccttoorryy ttoo “"“” ddooeess nnoott ffaaiill ?? Passing an argument of "” to ->ccwwdd(()) has the same affect of calling ->ccwwdd(()) without any arguments. Turn on Debug (_S_e_e _b_e_l_o_w) 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.
II aamm bbeehhiinndd aa SSOOCCKKSS ffiirreewwaallll,, bbuutt tthhee FFiirreewwaallll ooppttiioonn ddooeess nnoott wwoorrkk ?? 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 SOCKS firewall you must create a socks-ified perl executable by
compiling perl with the socks library.
II aamm bbeehhiinndd aann FFTTPP pprrooxxyy ffiirreewwaallll,, bbuutt ccaannnnoott aacccceessss mmaacchhiinneess oouuttssiiddee ?? 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.
MMyy ffttpp pprrooxxyy ffiirreewwaallll ddooeess nnoott lliisstteenn oonn ppoorrtt 2211 FTP servers usually listen on the same port number, port 21, as any other FTP server. But there is no reason why this has to be the case.
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.
IIss iitt ppoossssiibbllee ttoo cchhaannggee tthhee ffiillee ppeerrmmiissssiioonnss ooff aa ffiillee oonn aann FFTTPP sseerrvveerr ?? The answer to this is “maybe”. The FTP protocol does not specify a command to change file permissions on a remote host. However many servers do allow you to run the chmod command via the “SITE” command. This can be done with
$ftp->site('chmod','0775',$file);
II hhaavvee sseeeenn ssccrriippttss ccaallll aa mmeetthhoodd mmeessssaaggee,, bbuutt ccaannnnoott ffiinndd iitt ddooccuummeenntteedd ?? 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.
WWhhyy ddooeess NNeett::::FFTTPP nnoott iimmpplleemmeenntt mmppuutt aanndd mmggeett mmeetthhooddss 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;
} }
UUssiinngg NNeett::::SSMMTTPP WWhhyy ccaann’’tt tthhee ppaarrtt ooff aann EEmmaaiill aaddddrreessss aafftteerr tthhee @@ bbee uusseedd aass tthhee hhoossttnnaammee ?? 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 a DNS MX lookup
WWhhyy ddooeess NNeett::::SSMMTTPP nnoott ddoo DDNNSS MMXX llooookkuuppss ?? Net::SMTP implements the SMTP protocol. The DNS MX lookup is not part of this protocol.
TThhee vveerriiffyy mmeetthhoodd aallwwaayyss rreettuurrnnss ttrruuee ?? 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.
DDeebbuuggggiinngg ssccrriippttss HHooww ccaann II ddeebbuugg mmyy ssccrriippttss tthhaatt uussee NNeett:::: mmoodduulleess ?? 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 STDERR. This trace can be useful to see what commands are being sent to the remote server and what responses are being received back.
#!/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.
AAUUTTHHOORR AANNDD CCOOPPYYRRIIGGHHTT #
Copyright (C) 1997-1998 Graham Barr. All rights reserved.
perl v5.36.3 2023-02-15 Net::libnetFAQ(3p)