daemon/images/image.go
package images // import "github.com/docker/docker/daemon/images"
import (
"context"
"encoding/json"
"fmt"
"io"
"github.com/containerd/containerd/content"
"github.com/containerd/containerd/images"
"github.com/containerd/containerd/leases"
cerrdefs "github.com/containerd/errdefs"
"github.com/containerd/log"
"github.com/containerd/platforms"
"github.com/distribution/reference"
"github.com/docker/docker/api/types/backend"
"github.com/docker/docker/errdefs"
"github.com/docker/docker/image"
"github.com/opencontainers/go-digest"
ocispec "github.com/opencontainers/image-spec/specs-go/v1"
"github.com/pkg/errors"
)
// ErrImageDoesNotExist is error returned when no image can be found for a reference.
type ErrImageDoesNotExist struct {
Ref reference.Reference
}
func (e ErrImageDoesNotExist) Error() string {
ref := e.Ref
if named, ok := ref.(reference.Named); ok {
ref = reference.TagNameOnly(named)
}
return fmt.Sprintf("No such image: %s", reference.FamiliarString(ref))
}
// NotFound implements the NotFound interface
func (e ErrImageDoesNotExist) NotFound() {}
type manifestList struct {
Manifests []ocispec.Descriptor `json:"manifests"`
}
type manifest struct {
Config ocispec.Descriptor `json:"config"`
}
func (i *ImageService) PrepareSnapshot(ctx context.Context, id string, parentImage string, platform *ocispec.Platform, setupInit func(string) error) error {
// Only makes sense when containerd image store is used
panic("not implemented")
}
func (i *ImageService) manifestMatchesPlatform(ctx context.Context, img *image.Image, platform ocispec.Platform) (bool, error) {
ls, err := i.leases.ListResources(ctx, leases.Lease{ID: imageKey(img.ID().String())})
if err != nil {
if cerrdefs.IsNotFound(err) {
return false, nil
}
log.G(ctx).WithFields(log.Fields{
"error": err,
"image": img.ID,
"desiredPlatform": platforms.Format(platform),
}).Error("Error looking up image leases")
return false, err
}
// Note we are comparing against manifest lists here, which we expect to always have a CPU variant set (where applicable).
// So there is no need for the fallback matcher here.
comparer := platforms.Only(platform)
var (
ml manifestList
m manifest
)
makeRdr := func(ra content.ReaderAt) io.Reader {
return io.LimitReader(io.NewSectionReader(ra, 0, ra.Size()), 1e6)
}
for _, r := range ls {
logger := log.G(ctx).WithFields(log.Fields{
"image": img.ID,
"desiredPlatform": platforms.Format(platform),
"resourceID": r.ID,
"resourceType": r.Type,
})
logger.Debug("Checking lease resource for platform match")
if r.Type != "content" {
continue
}
ra, err := i.content.ReaderAt(ctx, ocispec.Descriptor{Digest: digest.Digest(r.ID)})
if err != nil {
if cerrdefs.IsNotFound(err) {
continue
}
logger.WithError(err).Error("Error looking up referenced manifest list for image")
continue
}
data, err := io.ReadAll(makeRdr(ra))
ra.Close()
if err != nil {
logger.WithError(err).Error("Error reading manifest list for image")
continue
}
ml.Manifests = nil
if err := json.Unmarshal(data, &ml); err != nil {
logger.WithError(err).Error("Error unmarshalling content")
continue
}
for _, md := range ml.Manifests {
switch md.MediaType {
case ocispec.MediaTypeImageManifest, images.MediaTypeDockerSchema2Manifest:
default:
continue
}
p := ocispec.Platform{
Architecture: md.Platform.Architecture,
OS: md.Platform.OS,
Variant: md.Platform.Variant,
}
if !comparer.Match(p) {
logger.WithField("otherPlatform", platforms.Format(p)).Debug("Manifest is not a match")
continue
}
// Here we have a platform match for the referenced manifest, let's make sure the manifest is actually for the image config we are using.
ra, err := i.content.ReaderAt(ctx, ocispec.Descriptor{Digest: md.Digest})
if err != nil {
logger.WithField("otherDigest", md.Digest).WithError(err).Error("Could not get reader for manifest")
continue
}
data, err := io.ReadAll(makeRdr(ra))
ra.Close()
if err != nil {
logger.WithError(err).Error("Error reading manifest for image")
continue
}
if err := json.Unmarshal(data, &m); err != nil {
logger.WithError(err).Error("Error desserializing manifest")
continue
}
if m.Config.Digest == img.ID().Digest() {
logger.WithField("manifestDigest", md.Digest).Debug("Found matching manifest for image")
return true, nil
}
logger.WithField("otherDigest", md.Digest).Debug("Skipping non-matching manifest")
}
}
return false, nil
}
func (i *ImageService) GetImageManifest(ctx context.Context, refOrID string, options backend.GetImageOpts) (*ocispec.Descriptor, error) {
panic("not implemented")
}
// GetImage returns an image corresponding to the image referred to by refOrID.
func (i *ImageService) GetImage(ctx context.Context, refOrID string, options backend.GetImageOpts) (retImg *image.Image, retErr error) {
defer func() {
if retErr != nil || retImg == nil || options.Platform == nil {
return
}
imgPlat := ocispec.Platform{
OS: retImg.OS,
Architecture: retImg.Architecture,
Variant: retImg.Variant,
}
p := *options.Platform
// Note that `platforms.Only` will fuzzy match this for us
// For example: an armv6 image will run just fine on an armv7 CPU, without emulation or anything.
if OnlyPlatformWithFallback(p).Match(imgPlat) {
return
}
// In some cases the image config can actually be wrong (e.g. classic `docker build` may not handle `--platform` correctly)
// So we'll look up the manifest list that corresponds to this image to check if at least the manifest list says it is the correct image.
var matches bool
matches, retErr = i.manifestMatchesPlatform(ctx, retImg, p)
if matches || retErr != nil {
return
}
// This allows us to tell clients that we don't have the image they asked for
// Where this gets hairy is the image store does not currently support multi-arch images, e.g.:
// An image `foo` may have a multi-arch manifest, but the image store only fetches the image for a specific platform
// The image store does not store the manifest list and image tags are assigned to architecture specific images.
// So we can have a `foo` image that is amd64 but the user requested armv7. If the user looks at the list of images.
// This may be confusing.
// The alternative to this is to return an errdefs.Conflict error with a helpful message, but clients will not be
// able to automatically tell what causes the conflict.
imgName := refOrID
if ref, err := reference.ParseNamed(refOrID); err == nil {
imgName = reference.FamiliarString(ref)
}
retErr = errdefs.NotFound(errors.Errorf("image with reference %s was found but its platform (%s) does not match the specified platform (%s)", imgName, platforms.Format(imgPlat), platforms.Format(p)))
}()
ref, err := reference.ParseAnyReference(refOrID)
if err != nil {
return nil, errdefs.InvalidParameter(err)
}
namedRef, ok := ref.(reference.Named)
if !ok {
digested, ok := ref.(reference.Digested)
if !ok {
return nil, ErrImageDoesNotExist{Ref: ref}
}
if img, err := i.imageStore.Get(image.ID(digested.Digest())); err == nil {
return img, nil
}
return nil, ErrImageDoesNotExist{Ref: ref}
}
if dgst, err := i.referenceStore.Get(namedRef); err == nil {
// Search the image stores to get the operating system, defaulting to host OS.
if img, err := i.imageStore.Get(image.ID(dgst)); err == nil {
return img, nil
}
}
// Search based on ID
if id, err := i.imageStore.Search(refOrID); err == nil {
img, err := i.imageStore.Get(id)
if err != nil {
return nil, ErrImageDoesNotExist{Ref: ref}
}
return img, nil
}
return nil, ErrImageDoesNotExist{Ref: ref}
}
// OnlyPlatformWithFallback uses `platforms.Only` with a fallback to handle the case where the platform
// being matched does not have a CPU variant.
//
// The reason for this is that CPU variant is not even if the official image config spec as of this writing.
// See: https://github.com/opencontainers/image-spec/pull/809
// Since Docker tends to compare platforms from the image config, we need to handle this case.
func OnlyPlatformWithFallback(p ocispec.Platform) platforms.Matcher {
return &onlyFallbackMatcher{only: platforms.Only(p), p: platforms.Normalize(p)}
}
type onlyFallbackMatcher struct {
only platforms.Matcher
p ocispec.Platform
}
func (m *onlyFallbackMatcher) Match(other ocispec.Platform) bool {
if m.only.Match(other) {
// It matches, no reason to fallback
return true
}
if other.Variant != "" {
// If there is a variant then this fallback does not apply, and there is no match
return false
}
otherN := platforms.Normalize(other)
otherN.Variant = "" // normalization adds a default variant... which is the whole problem with `platforms.Only`
return m.p.OS == otherN.OS &&
m.p.Architecture == otherN.Architecture
}