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).

import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Ssh;

public class ChilkatExample {

    public static void main(String[] args) {
        // 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.

        Ssh ssh = new Ssh();

        int sshPort = 22;
        try {
            ssh.connect("ssh.example.com", sshPort);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            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.
        String password = "mySshPassword";

        try {
            ssh.authenticatePw("mySshLogin", password);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        int channelNum = ssh.openSessionChannel();
        if (channelNum < 0) {
            System.out.println(ssh.getLastErrorText());
            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.
        try {
            ssh.sendReqShell(channelNum);

            ssh.channelSendString(channelNum, "cat /var/log/syslog\n", "utf-8");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            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.
        int pollTimeoutMs = 500;
        int 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.
        int result = ssh.channelReadAndPoll2(channelNum, pollTimeoutMs, maxNumBytes);
        if (result == -1) {
            System.out.println(ssh.getLastErrorText());
            return;
        }

        if (result == -2) {
            System.out.println("No channel data arrived before the timeout.");
        }

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

        if (result > 0) {
            System.out.println("Total bytes buffered: " + result);
        }

        String output;
        try {
            output = ssh.getReceivedText(channelNum, "utf-8");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println(output);

        ssh.disconnect();
    }
}