Function blobPipelineDetectCompressionStep

copy/compression.go:47–80

blobPipelineDetectCompressionStep updates *stream to detect its current compression format. srcInfo is only used for error messages. Returns data for other steps.

(stream *sourceStream, srcInfo types.BlobInfo)

// srcInfo is only used for error messages.
// Returns data for other steps.
func blobPipelineDetectCompressionStep(stream *sourceStream, srcInfo types.BlobInfo) (bpDetectCompressionStepData, error) {
	// This requires us to “peek ahead” into the stream to read the initial part, which requires us to chain through another io.Reader returned by DetectCompression.
	format, decompressor, reader, err := compression.DetectCompressionFormat(stream.reader) // We could skip this in some cases, but let's keep the code path uniform
	if err != nil {
		return bpDetectCompressionStepData{}, fmt.Errorf("reading blob %s: %w", srcInfo.Digest, err)
	}
	stream.reader = reader

	if decompressor != nil && format.Name() == compressiontypes.ZstdAlgorithmName {
		tocDigest, err := chunkedToc.GetTOCDigest(srcInfo.Annotations)
		if err != nil {
			return bpDetectCompressionStepData{}, err
		}
		if tocDigest != nil {
			format = compression.ZstdChunked
		}

	}
	res := bpDetectCompressionStepData{
		isCompressed: decompressor != nil,
		format:       format,
		decompressor: decompressor,
	}
	if res.isCompressed {
		res.srcCompressorBaseVariantName = format.BaseVariantName()
	} else {
		res.srcCompressorBaseVariantName = internalblobinfocache.Uncompressed
	}

	if expectedBaseFormat, known := expectedBaseCompressionFormats[stream.info.MediaType]; known && res.isCompressed && format.BaseVariantName() != expectedBaseFormat.Name() {
		logrus.Debugf("blob %s with type %s should be compressed with %s, but compressor appears to be %s", srcInfo.Digest.String(), srcInfo.MediaType, expectedBaseFormat.Name(), format.Name())
	}
	return res, nil
}

// bpCompressionStepData contains data that the copy pipeline needs about the compression step.
type bpCompressionStepData struct {