TheSignPainter98 / mendax

A CLI spoofer

Mendax

A simple terminal spoofer—like asciinema but usable in real-time. Specify inputs to fake and outputs to fake, all of which may be checked before running.

Table of Contents

• Why?
• Installation
• Not sure where to start?
• Writing the lie
• Author, License and Name

Why?

In my experience, a demo of a product is far more likely to break than production code. If code is in production, it’s likely gone through many layers of testing and checking so there’s a pretty good chance it does what it says on the tin. If code is used in demos, suddenly, it’s a completly different matter. Perhaps that minor change you made just fixing ‘that one last thing’ before the presentation turns out to break something critical. Perhaps your internet connection decides it just doesn’t want to work anymore, despite being fine ten minutes earlier. Suddenly, due factors which may be beyond your control, you’re now awkwardly filling time trying to fix code, questioning both the program itself and the life choices which led up to this moment.

Well no more.

Mendax offers:

• Sandboxed spoofing—unless you specifically allow it, mendax runs in a complete sandbox, unable to read or alter the host system’s state. No more surprises!
• Dry running—demos can be checked ahead of time. Higher quality in less development time.
• Time travel—tag important moments in the demo so you can jump between them at showtime. Adapt to your audience.

Oh and one more thing, do you creating asciinema recordings and getting annoyed at your typing speed and spelling mistakes? Well I do, and quite a bit; what should be a five minute job can stretch for far longer as I stress about the tiniest details. All this can go away just by running—

asciinema rec -c mendax

Installation

There is a snap! Simply install it by running

sudo snap install mendax

To build and install from the source, use

git clone https://github.com/TheSignPainter98/mendax
cd mendax
cargo install --path .
sudo install -m755 ./target/release/mendax /usr/bin/mendax

Not sure where to start?

Run mendax --init to create a new example lie, then run mendax for a quick demo.

Writing the lie

The lie to be told by mendax is specified in the form of a Rhai scriptlet. Declarations are made by calling methods on the given lie.

To pretend to run a command foo, use lie.run. This has three forms: the first will pretend to run foo printing no output, the second will spoof foo printing bar to its stdout and the third will do the same but with bar and baz being printed with a (by default) small delay between.

lie.run("foo");
lie.run("foo", "bar");
lie.run("foo", ["bar", "baz"]);

To pretend to cd into a given directory (and hence update the prompt), use lie.cd.

lie.cd("/dir");

To show some text, use lie.show.

lie.show("foo");

To pretend to type a string, use lie.enter. This is similar to lie.run but without the terminal prompt being shown.

To open another screen and run more lie commands in there use lie.screen. This method has two forms, where the last argument is always a closure which is passed a lie. The first argument is optionally a command to pretend to run.

lie.screen(|lie| {
    lie.show("I’m in another screen!");
});
lie.screen("man foo", |lie| {
    lie.show("I’m in another screen, pretending to be the manual page for foo");
});

To tag a point in the lie to be returned to later (by pressing / when output pauses, use lie.tag.

lie.tag("something-interesting");

To clear the screen use lie.clear. This takes no arguments.

lie.clear()

To pause an application at a given point, use lie.pause. This takes no arguments.

lie.pause()

To stop execution early, use lie.stop. This takes no arguments and is useful with jumps as it allows for optional presentation parts.

lie.stop()

To change the look and feel of the lie, use lie.look. This takes a map which contains the values the user wishes to change.

lie.look(#[ // Note: all fields are optional
    title: "foo"        // Set the title of the terminal window
    cwd: "/bar",        // Set prompt directory
    user: "methos",     // Set prompt user
    host: "gaia",       // Set prompt host
    speed: 100,         // Set the typing speed
    final_prompt: true, // Set whether a final prompt is displayed
})

To actually run commands and make changes on the underlying system, use lie.system, however, these are disabled by default. To enable system calls, pass the --unleash flag and go play in dangerous mode. The lie.system method has two forms. The first takes a single string, pretends to type it then runs it on the host. The second takes two strings, the first of which is the fake command to type and the second of which is the command to actually run and which is hidden from the user.

lie.system("ls");
lie.system("echo foo", "ls");

Author, License and Name

This project is maintained by Ed Jones and is licensed under the GNU General Public License version 3.

The name ‘mendax’ is a Latin word which roughly translates to ‘narrator,’ ‘storyteller,’ or ‘habitual liar.’ Exactly which meaning is the most appropriate is left as an exercise for the reader.