rscel's Introduction

rscel

RsCel is a CEL evaluator written in Rust. CEL is a google project that describes a turing-incomplete language that can be used to evaluate a user provdided expression. The language specification can be found here.

The design goals of this project were are as follows:

Flexible enough to allow for a user to bend the spec if needed
Sandbox'ed in such a way that only specific values can be bound
Can be used as a wasm depenedency (or other ffi)

The basic example of how to use:

use rscel::{CelContext, BindContext};

let mut ctx = CelContext::new();
let mut exec_ctx = BindContext::new();

ctx.add_program_str("main", "foo + 3").unwrap();
exec_ctx.bind_param("foo", 3.into()); // convert to CelValue

let res = ctx.exec("main", &exec_ctx).unwrap(); // CelValue::Int(6)
assert_eq!(res, 6.into());

As of 0.10.0 binding protobuf messages from the protobuf crate is now available! Given the following protobuf message:

message Point {
  int32 x = 1;
  int32 y = 2;
}

The following code can be used to evaluate a CEL expression on a Point message:

use rscel::{CelContext, BindContext};

// currently rscel required protobuf messages to be in a box 
let p = Box::new(protos::Point::new());
p.x = 4;
p.y = 5;

let mut ctx = CelContext::new();
let mut exec_ctx = BindContext::new();

ctx.add_program_str("main", "p.x + 3").unwrap();
exec_ctx.bind_protobuf_msg("p", p);

assert_eq!(ctx.exec("main", &exec_ctx), 7.into());