# Regorus

**Regorus** is 

  - *Rego*-*Rus(t)*  - A fast, light-weight [Rego](https://www.openpolicyagent.org/docs/latest/policy-language/) interpreter written in Rust.
  - *Rigorous* - A rigorous enforcer of well-defined Rego semantics.

Regorus is available as a library that can be easily integrated into your Rust projects.


> **Warning**
> While Regorus is highly performant and can interpret complex Rego policies, it does not yet pass the full [OPA test-suite](https://www.openpolicyagent.org/docs/latest/ir/#test-suite).
> We are actively working to achieve full OPA compliance. Meanwhile, Regorus should be considered
> **experimental and used with discretion**.

## Getting Started

[regorus](examples/regorus.rs) is an example program that shows how to integrate Regorus into your project and evaluate Rego policies.

To build it, do

    cargo build -r --example regorus


Check that the regorus example program is working

    $ target/release/examples/regorus
    Usage: regorus <COMMAND>
    
    Commands:
      eval   Evaluate a Rego Query
      lex    Tokenize a Rego policy
      parse  Parse q Rego policy
      help   Print this message or the help of the given subcommand(s)

    Options:
      -h, --help     Print help
      -V, --version  Print version


First, let's evaluate a simple Rego expression `1*2+3`

    target/release/examples/regorus eval "1*2+3"

This produces the following output

    {
      "result": [
        {
          "expressions": [
            {
               "value": 5,
               "text": "1*2+3",
               "location": {
                 "row": 1,
                 "col": 1
              }
            }
          ]
        }
      ]
    }

Next, evaluate a sample [policy](examples/example.rego) and [input](examples/input.json) (borrowed from [Rego tutorial](https://www.openpolicyagent.org/docs/latest/#2-try-opa-eval)):

    target/release/examples/regorus eval -d examples/example.rego -i examples/input.json data.example

Finally, evaluate real-world [policies](tests/aci/) used in Azure Container Instances (ACI)

    target/release/examples/regorus eval -d tests/aci/framework.rego \
        -d tests/aci/policy.rego \
        -d tests/aci/api.rego  \
        -d tests/aci/data.json  \
        -i tests/aci/input.json \
         data.policy.mount_overlay=x


## ACI Policies

Regorus successfully passes the ACI policy test-suite. It is fast and can run each of the tests in a few milliseconds.

    $ cargo test -r --test aci
        Finished release [optimized + debuginfo] target(s) in 0.05s
         Running tests/aci/main.rs (target/release/deps/aci-2cd8d21a893a2450)
    aci/mount_device                                  passed    3.863292ms
    aci/mount_overlay                                 passed    3.6905ms
    aci/scratch_mount                                 passed    3.643041ms
    aci/create_container                              passed    5.046333ms
    aci/shutdown_container                            passed    3.632ms
    aci/scratch_unmount                               passed    3.631333ms
    aci/unmount_overlay                               passed    3.609916ms
    aci/unmount_device                                passed    3.626875ms
    aci/load_fragment                                 passed    4.045167ms

Run the ACI policies in the `tests/aci` directory, using data `tests/aci/data.json` and input `tests/aci/input.json`:

    target/release/examples/regorus eval \
         -b tests/aci \
         -d tests/aci/data.json \
         -i tests/aci/input.json \
         data.framework.mount_overlay=x

Verify that [OPA](https://github.com/open-policy-agent/opa/releases) produces the same output

    diff <(target/release/examples/regorus eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x) <(opa eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x)

## Performance

To check how fast Regorus runs on your system, first install a tool like [hyperfine](https://github.com/sharkdp/hyperfine).

   cargo install hyperfine

Then benchmark evaluation of the ACI policies,

    $ hyperfine "target/release/examples/regorus eval -b tests/aci -d tests/aci/data.json -i   tests/aci/input.json data.framework.mount_overlay=x"
    Benchmark 1: target/release/examples/regorus eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x
      Time (mean ± σ):       4.6 ms ±   0.2 ms    [User: 4.1 ms, System: 0.4 ms]
      Range (min … max):     4.4 ms …   6.0 ms    422 runs
 
Compare it with OPA

    $  hyperfine "opa eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x"
    Benchmark 1: opa eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x
      Time (mean ± σ):      45.2 ms ±   0.6 ms    [User: 68.8 ms, System: 5.1 ms]
      Range (min … max):    43.8 ms …  46.7 ms    62 runs


## Contributing

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For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or
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