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Stream Processors

Processor API

Processors are a binary API that works off of content streams.

The incoming content stream will be provided to the binary via STDIN and the stream processor is expected to output the processed stream on STDOUT. If errors are encountered, errors MUST be returned via STDERR with a non-zero exit status.

Additional information can be provided to stream processors via a payload. Payloads are marshaled as protobuf.Any types and can wrap any type of serialized data structure.

On Unix systems, the payload, if available, is provided on fd 3 for the process.

On Windows systems, the payload, if available, is provided via a named pipe with the pipe's path set as the value of the environment variable STREAM_PROCESSOR_PIPE.

Configuration

To configure stream processors for containerd, entries in the config file need to be made. The stream_processors field is a map so that users can chain together multiple processors to mutate content streams.

Processor Fields:

  • Key - ID of the processor, used for passing a specific payload to the processor.
  • accepts - Accepted media-types for the processor that it can handle.
  • returns - The media-type that the processor returns.
  • path - Path to the processor binary.
  • args - Arguments passed to the processor binary.
version = 2

[stream_processors]
  [stream_processors."io.containerd.processor.v1.pigz"]
	accepts = ["application/vnd.docker.image.rootfs.diff.tar.gzip"]
	returns = "application/vnd.oci.image.layer.v1.tar"
	path = "unpigz"
	args = ["-d", "-c"]