(Objective-C) TCP Socket through SSH Tunnel (Port Forwarding)

Demonstrates using Chilkat Socket to communicate to a TCP service through an SSH tunnel. This example will connect to an NIST time server and (using the old Time Protocol (RFC 868)), will read the current GMT time.

Note: This is not necessarily a recommended means for getting the current date/time. The most commonly used time protocol is the Network Time Protocol (RFC-1305). The intent of this example is to show how TCP communications can occur through an SSH tunnel.

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#import <CkoSocket.h>
#import <NSString.h>
#import <CkoDateTime.h>

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

CkoSocket *tunnel = [[CkoSocket alloc] init];

NSString *sshHostname = @"sftp.example.com";
int sshPort = 22;

// Connect to an SSH server and establish the SSH tunnel:
BOOL success = [tunnel SshOpenTunnel: sshHostname sshPort: [NSNumber numberWithInt: sshPort]];
if (success != YES) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}

// Authenticate with the SSH server via a login/password
// or with a public key.
// This example demonstrates SSH password authentication.
success = [tunnel SshAuthenticatePw: @"mySshLogin" sshPassword: @"mySshPassword"];
if (success != YES) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}

// OK, the SSH tunnel is setup.  Now open a channel within the tunnel.
// Once the channel is obtained, the Socket API may
// be used exactly the same as usual, except all communications
// are sent through the channel in the SSH tunnel.
// Any number of channels may be created from the same SSH tunnel.
// Multiple channels may coexist at the same time.

// Connect to an NIST time server and read the current date/time
CkoSocket *channel = 0;
int maxWaitMs = 4000;
BOOL useTls = NO;
channel = [tunnel SshOpenChannel: @"time-c.nist.gov" port: [NSNumber numberWithInt: 37] ssl: useTls maxWaitMs: [NSNumber numberWithInt: maxWaitMs]];
if (tunnel.LastMethodSuccess == NO) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}

// The time server will send a big-endian 32-bit integer representing
// the number of seconds since since 00:00 (midnight) 1 January 1900 GMT.
// The ReceiveInt32 method will receive a 4-byte integer, but returns
// YES or NO to indicate success.  If successful, the integer
// is obtained via the ReceivedInt property.
BOOL bigEndian = YES;
success = [channel ReceiveInt32: bigEndian];
if (success != YES) {
    NSLog(@"%@",channel.LastErrorText);

    return;
}

CkoDateTime *dt = [[CkoDateTime alloc] init];
[dt SetFromNtpTime: channel.ReceivedInt];

// Show the current local date/time
BOOL bLocalTime = YES;
NSLog(@"%@%@",@"Current local date/time: ",[dt GetAsRfc822: bLocalTime]);

// Close the SSH channel.
success = [channel Close: [NSNumber numberWithInt: maxWaitMs]];
if (success != YES) {
    NSLog(@"%@",channel.LastErrorText);

    return;
}

// It is possible to create a new channel from the existing SSH tunnel for the next connection:
// Any number of channels may be created from the same SSH tunnel.
// Multiple channels may coexist at the same time.
channel = [tunnel SshOpenChannel: @"time-a.nist.gov" port: [NSNumber numberWithInt: 37] ssl: useTls maxWaitMs: [NSNumber numberWithInt: maxWaitMs]];
if (tunnel.LastMethodSuccess == NO) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}

// Review the LastErrorText to see that the connection was made via the SSH tunnel:
NSLog(@"%@",tunnel.LastErrorText);

// Close the connection to time-a.nist.gov.  This is actually closing our channel
// within the SSH tunnel, but keeps the tunnel open for the next port-forwarded connection.
success = [channel Close: [NSNumber numberWithInt: maxWaitMs]];
if (success != YES) {
    NSLog(@"%@",channel.LastErrorText);

    return;
}

// Finally, close the SSH tunnel.
success = [tunnel SshCloseTunnel];
if (success != YES) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}

NSLog(@"%@",@"TCP SSH tunneling example completed.");