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.
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.
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