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SSH Tunnel TCP Socket Options

Demonstrates tuning the underlying TCP socket with the SoRcvBuf, SoSndBuf, TcpNoDelay, OutboundBindIpAddress, and OutboundBindPort properties. These normally should be left at their defaults.

Background: These are low-level knobs for specific situations. Larger send/receive buffers can improve throughput on high-bandwidth, high-latency ("long fat") links; TcpNoDelay disables Nagle's algorithm to cut latency for small interactive packets at the cost of efficiency; and binding the outbound socket to a specific local address or port is occasionally required by firewall rules or multi-homed hosts. Change them only with a concrete reason, since the defaults are tuned for the common case.

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const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // Demonstrates tuning the underlying TCP socket with the SshTunnel properties SoRcvBuf, SoSndBuf,
    // TcpNoDelay, OutboundBindIpAddress, and OutboundBindPort.
    //
    // These normally should be left at their defaults; adjust them only for specific performance or
    // networking requirements.

    const tunnel = try chilkat.SshTunnel.init();
    defer tunnel.deinit();

    // Socket send/receive buffer sizes, in bytes.  Larger buffers can help throughput on
    // high-latency links.
    tunnel.setSoRcvBuf(4194304);
    tunnel.setSoSndBuf(262144);

    // Disable Nagle's algorithm to reduce latency for small, interactive packets.
    tunnel.setTcpNoDelay(true);

    // Bind the outbound socket to a specific local address/port before connecting.  0 (the default)
    // lets the OS choose the local port; an empty address lets the OS choose the interface.
    tunnel.setOutboundBindIpAddress("192.168.1.50");
    tunnel.setOutboundBindPort(0);

    tunnel.setDestHostname("db.internal.example.com");
    tunnel.setDestPort(5432);

    const ssh_port = 22;
    tunnel.connect("ssh.example.com", ssh_port) catch {
        std.debug.print("{s}\n", .{try tunnel.getLastErrorText(alloc)});
        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.
    const password = "mySshPassword";

    tunnel.authenticatePw("mySshLogin", password) catch {
        std.debug.print("{s}\n", .{try tunnel.getLastErrorText(alloc)});
        return;
    };

    const listen_port = 1080;
    tunnel.beginAccepting(listen_port) catch {
        std.debug.print("{s}\n", .{try tunnel.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("Tunnel established with custom socket options.\n", .{});

    const wait_for_thread_exit = true;
    tunnel.closeTunnel(wait_for_thread_exit) catch {
        std.debug.print("{s}\n", .{try tunnel.getLastErrorText(alloc)});
        return;
    };
}