Objective-C

Open a direct-tcpip Channel (SSH Port Forwarding)

Demonstrates the Chilkat Ssh.OpenDirectTcpIpChannel method, which opens a direct-tcpip channel through the SSH server to a target host and port. The first argument is the target hostname and the second is the target port. It returns the channel number, or -1 on failure.

Background: This is SSH local port forwarding at the API level: the channel carries ordinary TCP traffic to a service that may be reachable only from the SSH server's network — a database, an internal web app, a message broker. The key detail is that the server resolves the target name, not your machine, so it must resolve and be reachable there. Supplying a numeric IPv4 address avoids remote DNS resolution entirely.

Chilkat Objective-C Downloads

Download Chilkat for Objective-C

Objective-C

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

BOOL success = NO;

//  Demonstrates the Ssh.OpenDirectTcpIpChannel method, which opens a direct-tcpip channel
//  through the SSH server to a target host and port.  The 1st argument is the target hostname
//  and the 2nd is the target port.  It returns the channel number, or -1 on failure.

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;
}

//  The target name is resolved by the SSH server, not by this computer, so it must be
//  reachable from the server's network.
NSString *targetHostname = @"db.internal.example.com";
int targetPort = 5432;
int channelNum = [[ssh OpenDirectTcpIpChannel: targetHostname port: [NSNumber numberWithInt: targetPort]] intValue];
if (channelNum < 0) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

NSLog(@"%@%d",@"Opened direct-tcpip channel: ",channelNum);

//  The channel now carries ordinary TCP data to the target, tunneled over SSH.

[ssh Disconnect];