Oracles experimental
WARNING
This is an experimental feature. The API and behaviour may change in future versions of Scarb. Oracles are currently available in scarb execute with the --experimental-oracles flag Support is also planned in future versions of cairo-test and snforge.
An oracle is an external process (like a script, binary, or web service) that exposes custom logic or data to a Cairo program at runtime. You use it to perform tasks the Cairo VM can't, such as accessing real-world data or executing complex, non-provable computations.
Using oracles
The oracle library provides a type-safe interface for interacting with external oracles in Cairo applications. Invoking oracles via this package is the recommended way, as it provides a well-tested, secure, and maintainable interface for oracle interactions.
The documentation for this package provides a bird's-eye overview, guidelines, and instructions on how to invoke oracles from Cairo code.
In the oracle repository there is also an end-to-end example showcasing the feature. It implements a simple Cairo executable script, that invokes an oracle written in Rust that runs as a child process.
Writing oracles
In Cairo, the oracle abstraction doesn't specify how to implement or execute oracles. Those are details that are specific to the executor being used. Oracles are invoked using generic connection strings with the following format:
protocol:connection paramsThe Scarb executor implements oracles as subprocesses that communicate using a stdio protocol.
In the oracle repository, you can find ready-to-use SDKs that ease writing oracles compatible with Scarb executor.