NAME

Net::SSH::Mechanize - asynchronous ssh command invocation

VERSION

This document describes Net::SSH::Mechanize version 0.1.1

SYNOPSIS

Somewhat like POE::Component::OpenSSH, SSH::Batch, Net::OpenSSH::Parallel, App::MrShell etc, but:

• It uses the asynchonous AnyEvent event framework.

• It aims to support sudoing smoothly.

Synchronous usage:

use Net::SSH::Mechanize;

# Create an instance. This will not log in yet.
# All but the host name below are optional.
# Your .ssh/config will be used as normal, so if you 
# define ssh settings for a host there they will be picked up.
my $ssh = Net::SSH::Mechanize->new(
    host => 'somewhere.com',
    user => 'jbloggs',
    password => 'secret',
    port => 22,
);

my $ssh->login;

my $output = $ssh->capture("id");

# If successful, $output now contains something like:
# uid=1000(jbloggs) gid=1000(jbloggs) groups=1000(jbloggs)

$output = $ssh->sudo_capture("id");

# If successful, $output now contains something like:
# uid=0(root) gid=0(root) groups=0(root)

$ssh->logout;

As you can see, Net::SSH::Mechanize instance connects to only one host. Net::SSH::Mechanize::Multi manages connections to many.

See below for further examples, and script/gofer in the distribution source for a working, usable example.

This is work in progress. Expect rough edges. Feedback appreciated.

DESCRIPTION

The point about using AnyEvent internally is that "blocking" method calls only block the current "thread", and so the above can be used in parallel with (for example) other ssh sessions in the same process (using AnyEvent, or Coro). Although a sub-process is spawned for each ssh command, the parent process manages the child processes asynchronously, without blocking or polling.

Here is an example of asynchronous usage, using the <AnyEvent-condvar>> API. Calls return an <AnyEvent::CondVar> instance, which you can call the usual ->recv and ->cb methods on to perform a blocking wait (within the current thread), or assign a callback to be called on completion (respectively). See AnyEvent.

This is effectively what the example in the synopsis is doing, behind the scenes.

use Net::SSH::Mechanize;

# Create an instance, as above.
my $ssh = Net::SSH::Mechanize->new(
    host => 'somewhere.com',
    user => 'jbloggs',
    password => 'secret',
    port => 22,
);

# Accessing ->capture calls ->login automatically.
my $condvar = AnyEvent->condvar;
$ssh->login_async->cb(sub {
    my ($session) = shift->recv;
    $session->capture_async("id")->cb(sub {
        my ($stderr_handle, $result) = shift->recv;

        $condvar->send($result);
    });
});

# ... this returns immediately.  The callbacks assigned will get
# invoked behind the scenes, and we just need to wait and collect
# the result handed to our $condvar.

my $result = $convar->recv;

# If successful, $output now contains something like:
# uid=1000(jbloggs) gid=1000(jbloggs) groups=1000(jbloggs)

$ssh->logout;

You would only need to use this asynchronous style if you wanted to interface with AnyEvent, and/or add some Expect-like interaction into the code.

However, see also Net::SSH::Mechanize::Multi for a more convenient way of running multiple ssh sessions in parallel. It uses Coro to provide a (cooperatively) threaded model.

gofer

The script/ sub-directory includes a command-line tool called gofer which is designed to accept a list of connection definitions, and execute shell commands supplied in the arguments in parallel on each. See the documentation in the script for more information.

JUSTIFICATION

The problem with all other SSH wrappers I've tried so far is that they do not cope well when you need to sudo. Some of them do it but unreliably (SSH::Batch), others allow it with some help, but then don't assist with parallel connections to many servers (Net::OpenSSH). The I tried POE::Component::OpenSSH, but I found the POE::Component::Generic implementation forced a painful programming style with long chains of functions, one for each step in an exchange with the ssh process.

Possibly I just didn't try them all, or hard enough, but I really needed something which could do the job, and fell back to re-inventing the wheel. Initial experiments with AnyEvent and AnyEvent::Subprocess showed a lot of promise, and the result is this.

CLASS METHODS

$obj = $class->new(%params)

Creates a new instance. Parameters is a hash or a list of key-value parameters. Valid parameter keys are:

connection_params

A Net::SSH::Mechanize::ConnectParams instance, which defines a host connection. If this is given, any individual connection parameters also supplied to the constructor (host, user, port or password), will be ignored.

If this is absent, a Net::SSH::Mechanize::ConnectParams instance is constructed from any other individual connection parameters - the minimum which must be supplied is hostname. See below.

host

The hostname to connect to. Either this or connection_params must be supplied.

user

The user account to log into. If not given, no user will be supplied to ssh (this typically means it will use the current user as default).

port

The port to connect to (ssh will default to 22 if this is not specificed).

password

The password to connect with. This is only required if authentication will be performed, either on log-in or when sudoing.

login_timeout

How long to wait before breaking a connection (in seconds). It is passed to AnyEvent-timer> handler, whose callback will terminate the session if the period is exceeded. This avoids hung connections when the remote end isn't answering, or isn't answering in a way that will allow Net::SSH::Mechanize to terminate.

The default is 30.

INSTANCE ATTRIBUTES

$params = $obj->connection_params

This is a read-only accessor for the connection_params instance passed to the constructor (or equivalently, constructed from the constructor parameters).

$session = $obj->session

This is read-only accessor to a lazily-instantiated Net::SSH::Mechanize::Session instance, which represents the ssh process. Accessing it causes the session to be created and the remote host to be logged into.

$obj->login_timeout($integer) =head2 $integer = $obj->login_timeout

This is a read-write accessor to the log-in timeout parameter passed to the constructor.

It is passed to Net::SSH::Mechanize::Session's constructor, so if you plan to modify it, do so before ->session has been instantiated or will not have any effect on anything thereafter.

INSTANCE METHODS

login =head2 login_async =head2 capture =head2 capture_async =head2 sudo_capture =head2 sudo_capture_async =head2 logout

These methods exist here for convenience; they delegate to the equivalent Net::SSH::Mechanize::Session methods.

SEE ALSO

There are a lot of related tools, and this is just in Perl. Probably the most similar are SSH::Batch, POE::Component::OpenSSH, and App::MrShell (which at the time of writing, I've not yet tried.) None use AnyEvent, so far as I can tell.

SSH::Batch, Net::OpenSSH, Net::OpenSSH::Parallel, Net::SSH, Net::SSH2," Net::SSH::Expect", Net::SSH::Perl, POE::Component::OpenSSH, App::MrShell.

AUTHOR

Nick Stokoe <wulee@cpan.org>

LICENCE AND COPYRIGHT

Copyright (c) 2011, Nick Stokoe <wulee@cpan.org>. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.

DISCLAIMER OF WARRANTY

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

cpanm Net::SSH::Mechanize

perl -MCPAN -e shell
install Net::SSH::Mechanize