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).

// 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.

let ssh = chilkat::Ssh::new();

let ssh_port = 22;
if ssh.connect("ssh.example.com", ssh_port).is_err() {
    println!("{}", ssh.last_error_text());
    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.
let password = "mySshPassword".to_string();

if ssh.authenticate_pw("mySshLogin", &password).is_err() {
    println!("{}", ssh.last_error_text());
    return;
}

let channel_num = ssh.open_session_channel();
if channel_num < 0 {
    println!("{}", ssh.last_error_text());
    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.
if ssh.send_req_shell(channel_num).is_err() {
    println!("{}", ssh.last_error_text());
    return;
}

if ssh.channel_send_string(channel_num, "cat /var/log/syslog\n", "utf-8").is_err() {
    println!("{}", ssh.last_error_text());
    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.
let poll_timeout_ms = 500;
let max_num_bytes = 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.
let result = ssh.channel_read_and_poll2(channel_num, poll_timeout_ms, max_num_bytes);
if result == -1 {
    println!("{}", ssh.last_error_text());
    return;
}

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

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

if result > 0 {
    println!("Total bytes buffered: {}", result);
}

let Ok(output) = ssh.get_received_text(channel_num, "utf-8") else {
    println!("{}", ssh.last_error_text());
    return;
};

println!("{}", output);

ssh.disconnect();