NAME

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

VERSION

version 0.1.3

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.

KNOWN ISSUES

"unexpected stderr from command: stderr output" in test output: Something I haven't yet figured out how to banish properly. However, it does appear to be harmless. Patches welcome.

AUTHOR

Nick Stokoe "<wulee@cpan.org>"

LICENCE AND COPYRIGHT

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.

POD ERRORS

Hey! The above document had some coding errors, which are explained below:

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