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 <CkoSsh.h>
#import <NSString.h>

BOOL success = NO;

//  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.

CkoSsh *ssh = [[CkoSsh alloc] init];

int sshPort = 22;
success = [ssh Connect: @"ssh.example.com" port: [NSNumber numberWithInt: sshPort]];
if (success == NO) {
    NSLog(@"%@",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.
NSString *password = @"mySshPassword";

success = [ssh AuthenticatePw: @"mySshLogin" password: password];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

int channelNum = [[ssh OpenSessionChannel] intValue];
if (channelNum < 0) {
    NSLog(@"%@",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: [NSNumber numberWithInt: channelNum]];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

success = [ssh ChannelSendString: [NSNumber numberWithInt: channelNum] strData: @"cat /var/log/syslog\n" charset: @"utf-8"];
if (success == NO) {
    NSLog(@"%@",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.
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: [NSNumber numberWithInt: channelNum] pollTimeoutMs: [NSNumber numberWithInt: pollTimeoutMs] maxNumBytes: [NSNumber numberWithInt: maxNumBytes]] intValue];
if (result == -1) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

if (result == -2) {
    NSLog(@"%@",@"No channel data arrived before the timeout.");
}

if (result == 0) {
    NSLog(@"%@",@"EOF or channel close was processed.  Buffered data may still remain.");
}

if (result > 0) {
    NSLog(@"%@%d",@"Total bytes buffered: ",result);
}

NSString *output = [ssh GetReceivedText: [NSNumber numberWithInt: channelNum] charset: @"utf-8"];
if (ssh.LastMethodSuccess == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

NSLog(@"%@",output);

[ssh Disconnect];