Trait Buildpack

pub trait Buildpack {
    type Platform: Platform;
    type Metadata: DeserializeOwned;
    type Error: Debug;

    // Required methods
    fn detect(
        &self,
        context: DetectContext<Self>,
    ) -> Result<DetectResult, Self::Error>;
    fn build(
        &self,
        context: BuildContext<Self>,
    ) -> Result<BuildResult, Self::Error>;

    // Provided method
    fn on_error(&self, error: Error<Self::Error>) { ... }
}

Represents a buildpack written with the libcnb framework.

To implement a buildpack with this framework, start by implementing this trait. Besides the main build and detect methods, it also holds associated types for the buildpack: the Platform it is targeting, the type for its metadata and the custom error type.

Required Associated Types

type Platform: Platform

The platform targeted by this buildpack. If no specific platform is targeted, consider using GenericPlatform as the type.

type Metadata: DeserializeOwned

The metadata type for this buildpack. This is the data within [metadata] of the buildpacks buildpack.toml. The framework will attempt to parse the data and will only continue if parsing succeeded. If you wish to use raw, untyped, TOML data instead, use GenericMetadata.

type Error: Debug

The error type for buildpack specific errors, usually an enum. Examples of values inside the enum are: MavenExecutionFailed, InvalidGemfileLock, IncompatiblePythonVersion. The framework itself has its own error type that contains more low-level errors that can occur during buildpack execution.

Required Methods

fn detect( &self, context: DetectContext<Self>, ) -> Result<DetectResult, Self::Error>

Detect logic for this buildpack. Directly corresponds to detect in the CNB buildpack interface.

fn build(&self, context: BuildContext<Self>) -> Result<BuildResult, Self::Error>

Build logic for this buildpack. Directly corresponds to build in the CNB buildpack interface.

Provided Methods

fn on_error(&self, error: Error<Self::Error>)

If an unhandled error occurred within the framework or the buildpack, this method will be called by the framework to allow custom, buildpack specific, code to run before exiting. Usually, this method is implemented by logging the error in a user friendly manner.

Implementations are not limited to just logging, for example, buildpacks might want to collect and send metrics about occurring errors to a central system.

The default implementation will simply print the error (using its Debug implementation) to stderr.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors