forked from containers/image
/
manifest.go
121 lines (106 loc) · 5.08 KB
/
manifest.go
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package copy
import (
"context"
"strings"
"github.com/containers/image/manifest"
"github.com/containers/image/types"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
)
// preferredManifestMIMETypes lists manifest MIME types in order of our preference, if we can't use the original manifest and need to convert.
// Prefer v2s2 to v2s1 because v2s2 does not need to be changed when uploading to a different location.
// Include v2s1 signed but not v2s1 unsigned, because docker/distribution requires a signature even if the unsigned MIME type is used.
var preferredManifestMIMETypes = []string{manifest.DockerV2Schema2MediaType, manifest.DockerV2Schema1SignedMediaType}
// orderedSet is a list of strings (MIME types in our case), with each string appearing at most once.
type orderedSet struct {
list []string
included map[string]struct{}
}
// newOrderedSet creates a correctly initialized orderedSet.
// [Sometimes it would be really nice if Golang had constructors…]
func newOrderedSet() *orderedSet {
return &orderedSet{
list: []string{},
included: map[string]struct{}{},
}
}
// append adds s to the end of os, only if it is not included already.
func (os *orderedSet) append(s string) {
if _, ok := os.included[s]; !ok {
os.list = append(os.list, s)
os.included[s] = struct{}{}
}
}
// determineManifestConversion updates ic.manifestUpdates to convert manifest to a supported MIME type, if necessary and ic.canModifyManifest.
// Note that the conversion will only happen later, through ic.src.UpdatedImage
// Returns the preferred manifest MIME type (whether we are converting to it or using it unmodified),
// and a list of other possible alternatives, in order.
func (ic *imageCopier) determineManifestConversion(ctx context.Context, destSupportedManifestMIMETypes []string, forceManifestMIMEType string) (string, []string, error) {
_, srcType, err := ic.src.Manifest(ctx)
if err != nil { // This should have been cached?!
return "", nil, errors.Wrap(err, "Error reading manifest")
}
normalizedSrcType := manifest.NormalizedMIMEType(srcType)
if srcType != normalizedSrcType {
logrus.Debugf("Source manifest MIME type %s, treating it as %s", srcType, normalizedSrcType)
srcType = normalizedSrcType
}
if forceManifestMIMEType != "" {
destSupportedManifestMIMETypes = []string{forceManifestMIMEType}
}
if len(destSupportedManifestMIMETypes) == 0 {
return srcType, []string{}, nil // Anything goes; just use the original as is, do not try any conversions.
}
supportedByDest := map[string]struct{}{}
for _, t := range destSupportedManifestMIMETypes {
supportedByDest[t] = struct{}{}
}
// destSupportedManifestMIMETypes is a static guess; a particular registry may still only support a subset of the types.
// So, build a list of types to try in order of decreasing preference.
// FIXME? This treats manifest.DockerV2Schema1SignedMediaType and manifest.DockerV2Schema1MediaType as distinct,
// although we are not really making any conversion, and it is very unlikely that a destination would support one but not the other.
// In practice, schema1 is probably the lowest common denominator, so we would expect to try the first one of the MIME types
// and never attempt the other one.
prioritizedTypes := newOrderedSet()
// First of all, prefer to keep the original manifest unmodified.
if _, ok := supportedByDest[srcType]; ok {
prioritizedTypes.append(srcType)
}
if !ic.canModifyManifest {
// We could also drop the !ic.canModifyManifest check and have the caller
// make the choice; it is already doing that to an extent, to improve error
// messages. But it is nice to hide the “if !ic.canModifyManifest, do no conversion”
// special case in here; the caller can then worry (or not) only about a good UI.
logrus.Debugf("We can't modify the manifest, hoping for the best...")
return srcType, []string{}, nil // Take our chances - FIXME? Or should we fail without trying?
}
// Then use our list of preferred types.
for _, t := range preferredManifestMIMETypes {
if _, ok := supportedByDest[t]; ok {
prioritizedTypes.append(t)
}
}
// Finally, try anything else the destination supports.
for _, t := range destSupportedManifestMIMETypes {
prioritizedTypes.append(t)
}
logrus.Debugf("Manifest has MIME type %s, ordered candidate list [%s]", srcType, strings.Join(prioritizedTypes.list, ", "))
if len(prioritizedTypes.list) == 0 { // Coverage: destSupportedManifestMIMETypes is not empty (or we would have exited in the “Anything goes” case above), so this should never happen.
return "", nil, errors.New("Internal error: no candidate MIME types")
}
preferredType := prioritizedTypes.list[0]
if preferredType != srcType {
ic.manifestUpdates.ManifestMIMEType = preferredType
} else {
logrus.Debugf("... will first try using the original manifest unmodified")
}
return preferredType, prioritizedTypes.list[1:], nil
}
// isMultiImage returns true if img is a list of images
func isMultiImage(ctx context.Context, img types.UnparsedImage) (bool, error) {
_, mt, err := img.Manifest(ctx)
if err != nil {
return false, err
}
return manifest.MIMETypeIsMultiImage(mt), nil
}