Objective-C

TCP Socket through SSH Tunnel (Port Forwarding)

See more Socket/SSL/TLS Examples

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.

Objective-C

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

BOOL success = NO;

//  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:
success = [tunnel SshOpenTunnel: sshHostname sshPort: [NSNumber numberWithInt: sshPort]];
if (success == NO) {
    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 == NO) {
    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
int maxWaitMs = 4000;
BOOL useTls = NO;
CkoSocket *channel = [[CkoSocket alloc] init];
success = [tunnel SshNewChannel: @"time-c.nist.gov" port: [NSNumber numberWithInt: 37] ssl: useTls maxWaitMs: [NSNumber numberWithInt: maxWaitMs] channel: channel];
if (success == 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
//  true or false to indicate success.  If successful, the integer
//  is obtained via the ReceivedInt property.
BOOL bigEndian = YES;
success = [channel ReceiveInt32: bigEndian];
if (success == NO) {
    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.
success = [tunnel SshNewChannel: @"time-a.nist.gov" port: [NSNumber numberWithInt: 37] ssl: useTls maxWaitMs: [NSNumber numberWithInt: maxWaitMs] channel: channel];
if (success == 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 == NO) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}

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