## Piston
Piston is the underlying engine for running untrusted and possibly malicious code that originates from
[EMKC Challenges](https://emkc.org/challenges) and
[EMKC Weekly Contests](https://emkc.org/contests). It's also used in the
[Engineer Man Discord Server](https://discord.gg/engineerman) via
[I Run Code](https://github.com/engineer-man/piston-bot) bot as well as 1300+ other servers.
To get it in your own server, go here: https://emkc.org/run.

#### Use Public API (new)
Requires no installation and you can use it immediately. Reference the Versions/Execute sections
below to learn about the request and response formats.
- `GET` `https://emkc.org/api/v1/piston/versions`
- `POST` `https://emkc.org/api/v1/piston/execute`

Important Note: The Piston API is rate limited to 5 requests per second

#### Cloning and System Dependencies
```
# clone and enter repo
git clone https://github.com/engineer-man/piston
cd piston/lxc

# centos/rhel dependencies:
yum install -y epel-release
yum install -y lxc lxc-templates debootstrap libvirt
systemctl start libvirtd

# ubuntu server 18.04 dependencies:
apt install lxc lxc-templates debootstrap libvirt0

# arch dependencies:
sudo pacman -S lxc libvirt unzip

# everything else:
# not documented, please open pull requests with commands for debian/arch/macos/etc
```

#### Installation (simple)
Coming soon

#### Installation (advanced/manual)
See `var/install.txt` for how to create a new LXC container and install all of the required
software.

#### CLI Usage
- `lxc/execute [language] [file path] [args]`

#### API Usage
To use the API, it must first be started. To start the API, run the following:
```
cd api
./start
```

#### Base URLs
When using the public Piston API, use:
```
https://emkc.org/api/v1/piston
```
For your own local installation, use:
```
http://127.0.0.1:2000
```

#### Versions Endpoint
`GET /versions`
This endpoint takes no input and returns a JSON array of the currently installed languages.

Truncated response sample:
```json
HTTP/1.1 200 OK
Content-Type: application/json

[
    {
        "name": "awk",
        "version": "1.3.3"
    },
    {
        "name": "bash",
        "version": "4.4.20"
    },
    {
        "name": "c",
        "version": "7.5.0"
    }
]
```

#### Execute Endpoint
`POST /execute`
This endpoint takes the following JSON payload and expects at least the language and source. If
source is not provided, a blank file is passed as the source. If no `args` are desired, it can either
be an empty array or left out entirely.
```json
{
    "language": "js",
    "source": "console.log(process.argv)",
    "args": [
        "1",
        "2",
        "3"
    ]
}
```
A typical response upon successful execution will contain the `language`, `version`, `output` which
is a combination of both `stdout` and `stderr` but in chronological order according to program output,
as well as separate `stdout` and `stderr`.
```json
HTTP/1.1 200 OK
Content-Type: application/json

{
    "ran": true,
    "language": "js",
    "version": "12.13.0",
    "output": "[ '/usr/bin/node',\n  '/tmp/code.code',\n  '1',\n  '2',\n  '3' ]",
    "stdout": "[ '/usr/bin/node',\n  '/tmp/code.code',\n  '1',\n  '2',\n  '3' ]",
    "stderr": ""
}
```
If an invalid language is supplied, a typical response will look like the following:
```json
HTTP/1.1 400 Bad Request
Content-Type: application/json

{
    "code": "unsupported_language",
    "message": "whatever is not supported by Piston"
}
```

#### Supported Languages
- awk
- bash
- brainfuck
- c
- cpp
- csharp
- deno
- erlang
- elixir
- emacs
- elisp
- go
- haskell
- java
- jelly
- julia
- kotlin
- lua
- nasm
- node
- paradoc
- perl
- php
- python2
- python3
- ruby
- rust
- swift
- typescript

#### Principle of Operation
Piston utilizes LXC as the primary mechanism for sandboxing. There is a small API written in Go which takes
in execution requests and executes them in the container. High level, the API writes
a temporary source and args file to `/tmp` and that gets mounted read-only along with the execution scripts into the container.
The source file is either ran or compiled and ran (in the case of languages like c, c++, c#, go, etc.).

#### Security
LXC provides a great deal of security out of the box in that it's separate from the system.
Piston takes additional steps to make it resistant to
various privilege escalation, denial-of-service, and resource saturation threats. These steps include:
- Disabling outgoing network interaction
- Capping max processes at 64 (resists `:(){ :|: &}:;`, `while True: os.fork()`, etc.)
- Capping max files at 2048 (resists various file based attacks)
- Mounting all resources read-only (resists `sudo rm -rf --no-preserve-root /`)
- Cleaning up all temp space after each execution (resists out of drive space attacks)
- Running as a variety of unprivileged users
- Capping runtime execution at 3 seconds
- Capping stdout to 65536 characters (resists yes/no bombs and runaway output)
- SIGKILLing misbehaving code

#### License
Piston is licensed under the MIT license.