Read an SSH Channel with a Byte Threshold

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Demonstrates the Chilkat Ssh.ChannelReadAndPoll2 method, which works like ChannelReadAndPoll but also returns once newly processed data brings the total buffered data to or above a byte threshold. The arguments are the channel number, the poll timeout, and the threshold.

The integer return value is -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or channel close was processed, or — when greater than 0 — the total bytes currently buffered for the channel (not the bytes newly received by this call).

use strict;
use warnings;
use Chilkat2;

# Demonstrates the Ssh.ChannelReadAndPoll2 method, which works like ChannelReadAndPoll but also
# returns once the total buffered data reaches or exceeds a byte threshold.  The 1st argument is
# the channel number, the 2nd is the poll timeout, and the 3rd is the byte threshold.

my $ssh = Chilkat2::Ssh->new;

my $sshPort = 22;
my $success = $ssh->Connect('ssh.example.com', $sshPort);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# Normally you would not hard-code the password in source.  You should instead obtain it
# from an interactive prompt, environment variable, or a secrets vault.
my $password = 'mySshPassword';

$success = $ssh->AuthenticatePw('mySshLogin', $password);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

my $channelNum = $ssh->OpenSessionChannel();
if ($channelNum < 0) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
# raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
# echo typed commands back, and skips interactive login scripts.  The output is therefore
# clean and easily parseable -- but because no prompt is ever sent, code must not wait for
# one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
$success = $ssh->SendReqShell($channelNum);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

$success = $ssh->ChannelSendString($channelNum, "cat /var/log/syslog\n", 'utf-8');
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# Return when output goes quiet for 500ms, or once about 64KB has been buffered.  The
# threshold is not a hard buffer limit -- a whole SSH packet may push the total above it.
my $pollTimeoutMs = 500;
my $maxNumBytes = 65536;
# The return value is: -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or
# channel close was processed, or the total number of buffered bytes when greater than 0.
my $result = $ssh->ChannelReadAndPoll2($channelNum, $pollTimeoutMs, $maxNumBytes);
if ($result == -1) {
    print $ssh->LastErrorText, "\n";
    exit;
}

if ($result == -2) {
    print "No channel data arrived before the timeout.\n";
}

if ($result == 0) {
    print "EOF or channel close was processed.  Buffered data may still remain.\n";
}

if ($result > 0) {
    print 'Total bytes buffered: ', $result, "\n";
}

my $output = $ssh->GetReceivedText($channelNum, 'utf-8');
if (!$ssh->LastMethodSuccess) {
    print $ssh->LastErrorText, "\n";
    exit;
}

print $output, "\n";

$ssh->Disconnect();