mediatypes.go

/*
   Copyright The containerd Authors.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package images

import (
	"context"
	"sort"
	"strings"

	"github.com/containerd/containerd/errdefs"
	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
)

// mediatype definitions for image components handled in containerd.
//
// oci components are generally referenced directly, although we may centralize
// here for clarity.
const (
	MediaTypeDockerSchema2Layer            = "application/vnd.docker.image.rootfs.diff.tar"
	MediaTypeDockerSchema2LayerForeign     = "application/vnd.docker.image.rootfs.foreign.diff.tar"
	MediaTypeDockerSchema2LayerGzip        = "application/vnd.docker.image.rootfs.diff.tar.gzip"
	MediaTypeDockerSchema2LayerForeignGzip = "application/vnd.docker.image.rootfs.foreign.diff.tar.gzip"
	MediaTypeDockerSchema2Config           = "application/vnd.docker.container.image.v1+json"
	MediaTypeDockerSchema2Manifest         = "application/vnd.docker.distribution.manifest.v2+json"
	MediaTypeDockerSchema2ManifestList     = "application/vnd.docker.distribution.manifest.list.v2+json"
	// Checkpoint/Restore Media Types
	MediaTypeContainerd1Checkpoint               = "application/vnd.containerd.container.criu.checkpoint.criu.tar"
	MediaTypeContainerd1CheckpointPreDump        = "application/vnd.containerd.container.criu.checkpoint.predump.tar"
	MediaTypeContainerd1Resource                 = "application/vnd.containerd.container.resource.tar"
	MediaTypeContainerd1RW                       = "application/vnd.containerd.container.rw.tar"
	MediaTypeContainerd1CheckpointConfig         = "application/vnd.containerd.container.checkpoint.config.v1+proto"
	MediaTypeContainerd1CheckpointOptions        = "application/vnd.containerd.container.checkpoint.options.v1+proto"
	MediaTypeContainerd1CheckpointRuntimeName    = "application/vnd.containerd.container.checkpoint.runtime.name"
	MediaTypeContainerd1CheckpointRuntimeOptions = "application/vnd.containerd.container.checkpoint.runtime.options+proto"
	// Legacy Docker schema1 manifest
	MediaTypeDockerSchema1Manifest = "application/vnd.docker.distribution.manifest.v1+prettyjws"
)

// DiffCompression returns the compression as defined by the layer diff media
// type. For Docker media types without compression, "unknown" is returned to
// indicate that the media type may be compressed. If the media type is not
// recognized as a layer diff, then it returns errdefs.ErrNotImplemented
func DiffCompression(ctx context.Context, mediaType string) (string, error) {
	base, ext := parseMediaTypes(mediaType)
	switch base {
	case MediaTypeDockerSchema2Layer, MediaTypeDockerSchema2LayerForeign:
		if len(ext) > 0 {
			// Type is wrapped
			return "", nil
		}
		// These media types may have been compressed but failed to
		// use the correct media type. The decompression function
		// should detect and handle this case.
		return "unknown", nil
	case MediaTypeDockerSchema2LayerGzip, MediaTypeDockerSchema2LayerForeignGzip:
		if len(ext) > 0 {
			// Type is wrapped
			return "", nil
		}
		return "gzip", nil
	case ocispec.MediaTypeImageLayer, ocispec.MediaTypeImageLayerNonDistributable:
		if len(ext) > 0 {
			switch ext[len(ext)-1] {
			case "gzip":
				return "gzip", nil
			}
		}
		return "", nil
	default:
		return "", errdefs.ErrNotImplemented
	}
}

// parseMediaTypes splits the media type into the base type and
// an array of sorted extensions
func parseMediaTypes(mt string) (string, []string) {
	if mt == "" {
		return "", []string{}
	}

	s := strings.Split(mt, "+")
	ext := s[1:]
	sort.Strings(ext)

	return s[0], ext
}

// IsLayerTypes returns true if the media type is a layer
func IsLayerType(mt string) bool {
	if strings.HasPrefix(mt, "application/vnd.oci.image.layer.") {
		return true
	}

	// Parse Docker media types, strip off any + suffixes first
	base, _ := parseMediaTypes(mt)
	switch base {
	case MediaTypeDockerSchema2Layer, MediaTypeDockerSchema2LayerGzip,
		MediaTypeDockerSchema2LayerForeign, MediaTypeDockerSchema2LayerForeignGzip:
		return true
	}
	return false
}

// IsKnownConfig returns true if the media type is a known config type
func IsKnownConfig(mt string) bool {
	switch mt {
	case MediaTypeDockerSchema2Config, ocispec.MediaTypeImageConfig,
		MediaTypeContainerd1Checkpoint, MediaTypeContainerd1CheckpointConfig:
		return true
	}
	return false
}