Question 1

Is CEL safe for evaluating user-provided expressions?

Accepted Answer

Yes, CEL is designed with safety in mind; it's non-Turing complete and side-effect free, preventing malicious code execution like infinite loops. However, always validate inputs and use proper sandboxing in the host environment for added security.

Question 2

How does CEL compare to Lua for embedded scripting?

Accepted Answer

CEL is lighter and safer due to its non-Turing completeness, offering predictable performance and no need for heavy sandboxing. Lua provides more flexibility with full scripting capabilities but requires sandboxing for safety, making CEL better for security-critical expression evaluation.

Question 3

Can CEL handle loops or iteration?

Accepted Answer

CEL supports only bounded iteration through macros like `all`, `exists`, and `map`, which are expanded at parse time. This ensures evaluation remains linear and safe, but it cannot handle unbounded loops or recursive functions.

Question 4

How to integrate CEL with Go structs for type-checking?

Accepted Answer

Use the `cel.Variable` environment option to expose variables with specific types, such as `cel.StringType` or custom protobuf types. The README shows examples with primitive and complex types, enabling static type-checking during compilation.

Question 5

What's the performance impact of enabling macros in CEL?

Accepted Answer

Macros are enabled by default and expand at parse time, adding some overhead during compilation but not during evaluation. Disabling macros can simplify parsing if bounded iteration features are not needed, potentially improving initial setup speed.

Question 6

How does partial evaluation work with unknown inputs?

Accepted Answer

CEL uses commutative logical operators (`&&`, `||`) to evaluate both sides even with errors or unknowns, allowing for graceful handling. This enables residual expressions to be generated for later evaluation, as explained in the partial state section of the README.

Question 7

Is CEL suitable for real-time policy evaluation in microservices?

Accepted Answer

Yes, CEL is designed for high-performance evaluation with linear scalability, making it ideal for real-time use cases like policy enforcement in microservices. Its thread-safe, side-effect free evaluation allows for efficient caching and reuse of compiled expressions.

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