Function newImageDestination

storage/storage_dest.go:142–188

newImageDestination sets us up to write a new image, caching blobs in a temporary directory until it's time to Commit() the image

(sys *types.SystemContext, imageRef storageReference)

// newImageDestination sets us up to write a new image, caching blobs in a temporary directory until
// it's time to Commit() the image
func newImageDestination(sys *types.SystemContext, imageRef storageReference) (*storageImageDestination, error) {
	directory, err := tmpdir.MkDirBigFileTemp(sys, "storage")
	if err != nil {
		return nil, fmt.Errorf("creating a temporary directory: %w", err)
	}
	dest := &storageImageDestination{
		PropertyMethodsInitialize: impl.PropertyMethods(impl.Properties{
			SupportedManifestMIMETypes: []string{
				imgspecv1.MediaTypeImageManifest,
				manifest.DockerV2Schema2MediaType,
				manifest.DockerV2Schema1SignedMediaType,
				manifest.DockerV2Schema1MediaType,
			},
			// We ultimately have to decompress layers to populate trees on disk
			// and need to explicitly ask for it here, so that the layers' MIME
			// types can be set accordingly.
			DesiredLayerCompression:        types.PreserveOriginal,
			AcceptsForeignLayerURLs:        false,
			MustMatchRuntimeOS:             true,
			IgnoresEmbeddedDockerReference: true, // Yes, we want the unmodified manifest
			HasThreadSafePutBlob:           true,
		}),

		imageRef:     imageRef,
		directory:    directory,
		signatureses: make(map[digest.Digest][]byte),
		metadata: storageImageMetadata{
			SignatureSizes:  []int{},
			SignaturesSizes: make(map[digest.Digest][]int),
		},
		indexToStorageID: make(map[int]string),
		lockProtected: storageImageDestinationLockProtected{
			indexToAddedLayerInfo: make(map[int]addedLayerInfo),

			indexToDiffID:    make(map[int]digest.Digest),
			indexToTOCDigest: make(map[int]digest.Digest),
			blobDiffIDs:      make(map[digest.Digest]digest.Digest),

			diffOutputs:            make(map[int]*graphdriver.DriverWithDifferOutput),
			indexToAdditionalLayer: make(map[int]storage.AdditionalLayer),
			filenames:              make(map[digest.Digest]string),
			fileSizes:              make(map[digest.Digest]int64),
		},
	}
	dest.Compat = impl.AddCompat(dest)
	return dest, nil
}

// Reference returns the reference used to set up this destination.  Note that this should directly correspond to user's intent,
// e.g. it should use the public hostname instead of the result of resolving CNAMEs or following redirects.