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).

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

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

    // 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.

    const ssh = try chilkat.Ssh.init();
    defer ssh.deinit();

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

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

    const channel_num = ssh.openSessionChannel();
    if (channel_num < 0) {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        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.
    ssh.sendReqShell(channel_num) catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    };

    ssh.channelSendString(channel_num, "cat /var/log/syslog\n", "utf-8") catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        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.
    const poll_timeout_ms = 500;
    const max_num_bytes = 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.
    const result = ssh.channelReadAndPoll2(channel_num, poll_timeout_ms, max_num_bytes);
    if (result == -1) {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    }

    if (result == -2) {
        std.debug.print("No channel data arrived before the timeout.\n", .{});
    }

    if (result == 0) {
        std.debug.print("EOF or channel close was processed.  Buffered data may still remain.\n", .{});
    }

    if (result > 0) {
        std.debug.print("Total bytes buffered: {d}\n", .{result});
    }

    const output = ssh.getReceivedText(alloc, channel_num, "utf-8") catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("{s}\n", .{output});

    ssh.disconnect();
}