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).

NODEJS_PRELUDE

function chilkatExample() {

    var success = false;

    //  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.

    var ssh = new chilkat.Ssh();

    var sshPort = 22;
    success = ssh.Connect("ssh.example.com",sshPort);
    if (success == false) {
        console.log(ssh.LastErrorText);
        return;
    }

    //  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.
    var password = "mySshPassword";

    success = ssh.AuthenticatePw("mySshLogin",password);
    if (success == false) {
        console.log(ssh.LastErrorText);
        return;
    }

    var channelNum = ssh.OpenSessionChannel();
    if (channelNum < 0) {
        console.log(ssh.LastErrorText);
        return;
    }

    //  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 == false) {
        console.log(ssh.LastErrorText);
        return;
    }

    success = ssh.ChannelSendString(channelNum,"cat /var/log/syslog\n","utf-8");
    if (success == false) {
        console.log(ssh.LastErrorText);
        return;
    }

    //  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.
    var pollTimeoutMs = 500;
    var 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.
    var result = ssh.ChannelReadAndPoll2(channelNum,pollTimeoutMs,maxNumBytes);
    if (result == -1) {
        console.log(ssh.LastErrorText);
        return;
    }

    if (result == -2) {
        console.log("No channel data arrived before the timeout.");
    }

    if (result == 0) {
        console.log("EOF or channel close was processed.  Buffered data may still remain.");
    }

    if (result > 0) {
        console.log("Total bytes buffered: " + result);
    }

    var output = ssh.GetReceivedText(channelNum,"utf-8");
    if (ssh.LastMethodSuccess == false) {
        console.log(ssh.LastErrorText);
        return;
    }

    console.log(output);

    ssh.Disconnect();

}

chilkatExample();