github.com/lalkh/containerd@v1.4.3/docs/stream_processors.md (about)

     1  # Stream Processors
     2  
     3  ## Processor API
     4  
     5  Processors are a binary API that works off of content streams.
     6  
     7  The incoming content stream will be provided to the binary via `STDIN`
     8  and the stream processor is expected to output the processed stream on
     9  `STDOUT`.  If errors are encountered, errors MUST be returned via `STDERR`
    10  with a non-zero exit status.
    11  
    12  Additional information can be provided to stream processors via a payload.
    13  Payloads are marshaled as `protobuf.Any` types and can wrap any type of
    14  serialized data structure.
    15  
    16  On Unix systems, the payload, if available, is provided on `fd 3` for the process.
    17  
    18  On Windows systems, the payload, if available, is provided via a named pipe with the
    19  pipe's path set as the value of the environment variable `STREAM_PROCESSOR_PIPE`.
    20  
    21  ## Configuration
    22  
    23  To configure stream processors for containerd, entries in the config file need to be made.
    24  The `stream_processors` field is a map so that users can chain together multiple processors
    25  to mutate content streams.
    26  
    27  Processor Fields:
    28  
    29  * Key - ID of the processor, used for passing a specific payload to the processor.
    30  * `accepts` - Accepted media-types for the processor that it can handle.
    31  * `returns` - The media-type that the processor returns.
    32  * `path` - Path to the processor binary.
    33  * `args` - Arguments passed to the processor binary.
    34  
    35  ```toml
    36  [stream_processors]
    37    [stream_processors."io.containerd.processor.v1.pigz"]
    38  	accepts = ["application/vnd.docker.image.rootfs.diff.tar.gzip"]
    39  	returns = "application/vnd.oci.image.layer.v1.tar"
    40  	path = "unpigz"
    41  	args = ["-d", "-c"]
    42  ```