Java

Read Data from an SSH Channel

Demonstrates the Chilkat Ssh.ChannelRead method, which reads incoming SSH channel messages. The only argument is the channel number; the ReadTimeoutMs property limits how long it waits. Received data is appended to the channel's receive buffer, then retrieved with a GetReceived... method.

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).

Background: SSH reading is a two-step pattern that trips people up at first: the Channel* read/poll methods move bytes from the network into an internal per-channel buffer, and a separate GetReceived... call hands that buffer to your code. A positive return is therefore a buffer total, not a count of what this call fetched. Note that a 0 return means EOF or close — buffered data can still remain and should be drained.

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

public class ChilkatExample {

    public static void main(String[] args) {
        // Demonstrates the Ssh.ChannelRead method, which reads incoming SSH channel messages.  The only
        // argument is the channel number.  The ReadTimeoutMs property limits how long it waits.

        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, "uname -a\n", "utf-8");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // 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.channelRead(channelNum);
        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();
    }
}