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package manifest
import (
"encoding/json"
"github.com/containers/libtrust"
digest "github.com/opencontainers/go-digest"
imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
)
// FIXME: Should we just use docker/distribution and docker/docker implementations directly?
// FIXME(runcom, mitr): should we have a mediatype pkg??
const (
// DockerV2Schema1MediaType MIME type represents Docker manifest schema 1
DockerV2Schema1MediaType = "application/vnd.docker.distribution.manifest.v1+json"
// DockerV2Schema1MediaType MIME type represents Docker manifest schema 1 with a JWS signature
DockerV2Schema1SignedMediaType = "application/vnd.docker.distribution.manifest.v1+prettyjws"
// DockerV2Schema2MediaType MIME type represents Docker manifest schema 2
DockerV2Schema2MediaType = "application/vnd.docker.distribution.manifest.v2+json"
// DockerV2Schema2ConfigMediaType is the MIME type used for schema 2 config blobs.
DockerV2Schema2ConfigMediaType = "application/vnd.docker.container.image.v1+json"
// DockerV2Schema2LayerMediaType is the MIME type used for schema 2 layers.
DockerV2Schema2LayerMediaType = "application/vnd.docker.image.rootfs.diff.tar.gzip"
// DockerV2SchemaLayerMediaTypeUncompressed is the mediaType used for uncompressed layers.
DockerV2SchemaLayerMediaTypeUncompressed = "application/vnd.docker.image.rootfs.diff.tar"
// DockerV2ListMediaType MIME type represents Docker manifest schema 2 list
DockerV2ListMediaType = "application/vnd.docker.distribution.manifest.list.v2+json"
// DockerV2Schema2ForeignLayerMediaType is the MIME type used for schema 2 foreign layers.
DockerV2Schema2ForeignLayerMediaType = "application/vnd.docker.image.rootfs.foreign.diff.tar"
// DockerV2Schema2ForeignLayerMediaType is the MIME type used for gzipped schema 2 foreign layers.
DockerV2Schema2ForeignLayerMediaTypeGzip = "application/vnd.docker.image.rootfs.foreign.diff.tar.gzip"
)
// GuessMIMEType guesses MIME type of a manifest and returns it _if it is recognized_, or "" if unknown or unrecognized.
// FIXME? We should, in general, prefer out-of-band MIME type instead of blindly parsing the manifest,
// but we may not have such metadata available (e.g. when the manifest is a local file).
// This is publicly visible as c/image/manifest.GuessMIMEType.
func GuessMIMEType(manifest []byte) string {
// A subset of manifest fields; the rest is silently ignored by json.Unmarshal.
// Also docker/distribution/manifest.Versioned.
meta := struct {
MediaType string `json:"mediaType"`
SchemaVersion int `json:"schemaVersion"`
Signatures any `json:"signatures"`
}{}
if err := json.Unmarshal(manifest, &meta); err != nil {
return ""
}
switch meta.MediaType {
case DockerV2Schema2MediaType, DockerV2ListMediaType,
imgspecv1.MediaTypeImageManifest, imgspecv1.MediaTypeImageIndex: // A recognized type.
return meta.MediaType
}
// this is the only way the function can return DockerV2Schema1MediaType, and recognizing that is essential for stripping the JWS signatures = computing the correct manifest digest.
switch meta.SchemaVersion {
case 1:
if meta.Signatures != nil {
return DockerV2Schema1SignedMediaType
}
return DockerV2Schema1MediaType
case 2:
// Best effort to understand if this is an OCI image since mediaType
// wasn't in the manifest for OCI image-spec < 1.0.2.
// For docker v2s2 meta.MediaType should have been set. But given the data, this is our best guess.
ociMan := struct {
Config struct {
MediaType string `json:"mediaType"`
} `json:"config"`
}{}
if err := json.Unmarshal(manifest, &ociMan); err != nil {
return ""
}
switch ociMan.Config.MediaType {
case imgspecv1.MediaTypeImageConfig:
return imgspecv1.MediaTypeImageManifest
case DockerV2Schema2ConfigMediaType:
// This case should not happen since a Docker image
// must declare a top-level media type and
// `meta.MediaType` has already been checked.
return DockerV2Schema2MediaType
}
// Maybe an image index or an OCI artifact.
ociIndex := struct {
Manifests []imgspecv1.Descriptor `json:"manifests"`
}{}
if err := json.Unmarshal(manifest, &ociIndex); err != nil {
return ""
}
if len(ociIndex.Manifests) != 0 {
if ociMan.Config.MediaType == "" {
return imgspecv1.MediaTypeImageIndex
}
// FIXME: this is mixing media types of manifests and configs.
return ociMan.Config.MediaType
}
// It's most likely an OCI artifact with a custom config media
// type which is not (and cannot) be covered by the media-type
// checks cabove.
return imgspecv1.MediaTypeImageManifest
}
return ""
}
// Digest returns the a digest of a docker manifest, with any necessary implied transformations like stripping v1s1 signatures.
// This is publicly visible as c/image/manifest.Digest.
func Digest(manifest []byte) (digest.Digest, error) {
if GuessMIMEType(manifest) == DockerV2Schema1SignedMediaType {
sig, err := libtrust.ParsePrettySignature(manifest, "signatures")
if err != nil {
return "", err
}
manifest, err = sig.Payload()
if err != nil {
// Coverage: This should never happen, libtrust's Payload() can fail only if joseBase64UrlDecode() fails, on a string
// that libtrust itself has josebase64UrlEncode()d
return "", err
}
}
return digest.FromBytes(manifest), nil
}
// MatchesDigest returns true iff the manifest matches expectedDigest.
// Error may be set if this returns false.
// Note that this is not doing ConstantTimeCompare; by the time we get here, the cryptographic signature must already have been verified,
// or we are not using a cryptographic channel and the attacker can modify the digest along with the manifest blob.
// This is publicly visible as c/image/manifest.MatchesDigest.
func MatchesDigest(manifest []byte, expectedDigest digest.Digest) (bool, error) {
// This should eventually support various digest types.
actualDigest, err := Digest(manifest)
if err != nil {
return false, err
}
return expectedDigest == actualDigest, nil
}
// NormalizedMIMEType returns the effective MIME type of a manifest MIME type returned by a server,
// centralizing various workarounds.
// This is publicly visible as c/image/manifest.NormalizedMIMEType.
func NormalizedMIMEType(input string) string {
switch input {
// "application/json" is a valid v2s1 value per https://github.com/docker/distribution/blob/master/docs/spec/manifest-v2-1.md .
// This works for now, when nothing else seems to return "application/json"; if that were not true, the mapping/detection might
// need to happen within the ImageSource.
case "application/json":
return DockerV2Schema1SignedMediaType
case DockerV2Schema1MediaType, DockerV2Schema1SignedMediaType,
imgspecv1.MediaTypeImageManifest,
imgspecv1.MediaTypeImageIndex,
DockerV2Schema2MediaType,
DockerV2ListMediaType:
return input
default:
// If it's not a recognized manifest media type, or we have failed determining the type, we'll try one last time
// to deserialize using v2s1 as per https://github.com/docker/distribution/blob/master/manifests.go#L108
// and https://github.com/docker/distribution/blob/master/manifest/schema1/manifest.go#L50
//
// Crane registries can also return "text/plain", or pretty much anything else depending on a file extension “recognized” in the tag.
// This makes no real sense, but it happens
// because requests for manifests are
// redirected to a content distribution
// network which is configured that way. See https://bugzilla.redhat.com/show_bug.cgi?id=1389442
return DockerV2Schema1SignedMediaType
}
}
|
