Method open

core/remotes/docker/fetcher.go:442–617

(ctx context.Context, req *request, mediatype string, offset int64, lastHost bool)

}

func (r dockerFetcher) open(ctx context.Context, req *request, mediatype string, offset int64, lastHost bool) (_ io.ReadCloser, _ int64, retErr error) {
	const minChunkSize = 512

	chunkSize := int64(r.performances.ConcurrentLayerFetchBuffer)
	parallelism := int64(r.performances.MaxConcurrentDownloads)
	if chunkSize < minChunkSize || req.body != nil {
		parallelism = 1
	}
	log.G(ctx).WithField("initial_parallelism", r.performances.MaxConcurrentDownloads).
		WithField("parallelism", parallelism).
		WithField("chunk_size", chunkSize).
		WithField("offset", offset).
		Debug("fetching layer")
	req.setMediaType(mediatype)
	req.header.Set("Accept-Encoding", "zstd;q=1.0, gzip;q=0.8, deflate;q=0.5")
	if parallelism > 1 || offset > 0 {
		req.setOffset(offset)
	}

	if err := r.Acquire(ctx, 1); err != nil {
		return nil, 0, err
	}
	var remaining int64
	resp, err := req.doWithRetries(ctx, lastHost, withErrorCheck, withOffsetCheck(offset, parallelism))
	switch err {
	case nil:
		// all good
		remaining = resp.ContentLength
	case errContentRangeIgnored:
		if parallelism != 1 {
			log.G(ctx).WithError(err).Info("remote host ignored content range, forcing parallelism to 1")
			parallelism = 1
		}
		remaining = resp.ContentLength - offset
	default:
		log.G(ctx).WithError(err).Debug("fetch failed")
		r.Release(1)
		return nil, 0, err
	}

	body := &fnOnClose{
		BeforeClose: func() {
			r.Release(1)
		},
		ReadCloser: resp.Body,
	}
	defer func() {
		if retErr != nil {
			body.Close()
		}
	}()

	encoding := strings.FieldsFunc(resp.Header.Get("Content-Encoding"), func(r rune) bool {
		return r == ' ' || r == '\t' || r == ','
	})

	if remaining <= chunkSize {
		parallelism = 1