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//
// Copyright 2021 The Sigstore 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 mutate
import (
"context"
"errors"
"fmt"
v1 "github.com/google/go-containerregistry/pkg/v1"
"github.com/google/go-containerregistry/pkg/v1/empty"
"github.com/google/go-containerregistry/pkg/v1/mutate"
"github.com/google/go-containerregistry/pkg/v1/types"
"github.com/sigstore/cosign/v2/pkg/oci"
)
// Fn is the signature of the callback supplied to Map.
// The oci.SignedEntity is either an oci.SignedImageIndex or an oci.SignedImage.
// This callback is called on oci.SignedImageIndex *before* its children are
// processed with a context that returns IsBeforeChildren(ctx) == true.
// If the images within the SignedImageIndex change after the Before pass, then
// the Fn will be invoked again on the new SignedImageIndex with a context
// that returns IsAfterChildren(ctx) == true.
// If the returned entity is nil, it is filtered from the result of Map.
type Fn func(context.Context, oci.SignedEntity) (oci.SignedEntity, error)
// ErrSkipChildren is a special error that may be returned from a Mutator
// to skip processing of an index's child entities.
var ErrSkipChildren = errors.New("skip child entities")
// Map calls `fn` on the signed entity and each of its constituent entities (`SignedImageIndex`
// or `SignedImage`) transitively.
// Any errors returned by an `fn` are returned by `Map`.
func Map(ctx context.Context, parent oci.SignedEntity, fn Fn) (oci.SignedEntity, error) {
parent, err := fn(before(ctx), parent)
switch {
case errors.Is(err, ErrSkipChildren):
return parent, nil
case err != nil:
return nil, err
case parent == nil:
// If the function returns nil, it filters it.
return nil, nil
}
sii, ok := parent.(oci.SignedImageIndex)
if !ok {
return parent, nil
}
im, err := sii.IndexManifest()
if err != nil {
return nil, err
}
// Track whether any of the child entities change.
changed := false
adds := []IndexAddendum{}
for _, desc := range im.Manifests {
switch desc.MediaType {
case types.OCIImageIndex, types.DockerManifestList:
x, err := sii.SignedImageIndex(desc.Digest)
if err != nil {
return nil, err
}
se, err := Map(ctx, x, fn)
if err != nil {
return nil, err
} else if se == nil {
// If the function returns nil, it filters it.
changed = true
continue
}
changed = changed || (x != se)
adds = append(adds, IndexAddendum{
Add: se.(oci.SignedImageIndex), // Must be an image index.
Descriptor: v1.Descriptor{
URLs: desc.URLs,
MediaType: desc.MediaType,
Annotations: desc.Annotations,
Platform: desc.Platform,
},
})
case types.OCIManifestSchema1, types.DockerManifestSchema2:
x, err := sii.SignedImage(desc.Digest)
if err != nil {
return nil, err
}
se, err := fn(ctx, x)
if err != nil {
return nil, err
} else if se == nil {
// If the function returns nil, it filters it.
changed = true
continue
}
changed = changed || (x != se)
adds = append(adds, IndexAddendum{
Add: se.(oci.SignedImage), // Must be an image
Descriptor: v1.Descriptor{
URLs: desc.URLs,
MediaType: desc.MediaType,
Annotations: desc.Annotations,
Platform: desc.Platform,
},
})
default:
return nil, fmt.Errorf("unknown mime type: %v", desc.MediaType)
}
}
if !changed {
return parent, nil
}
// Preserve the key attributes from the base IndexManifest.
e := mutate.IndexMediaType(empty.Index, im.MediaType)
e = mutate.Annotations(e, im.Annotations).(v1.ImageIndex)
// Construct a new ImageIndex from the new constituent signed images.
result := AppendManifests(e, adds...)
// Since the children changed, give the callback a crack at the new image index.
return fn(after(ctx), result)
}
// This is used to associate which pass of the Map a particular
// callback is being invoked for.
type mapPassKey struct{}
// before decorates the context such that IsBeforeChildren(ctx) is true.
func before(ctx context.Context) context.Context {
return context.WithValue(ctx, mapPassKey{}, "before")
}
// after decorates the context such that IsAfterChildren(ctx) is true.
func after(ctx context.Context) context.Context {
return context.WithValue(ctx, mapPassKey{}, "after")
}
// IsBeforeChildren is true within a Mutator when it is called before the children
// have been processed.
func IsBeforeChildren(ctx context.Context) bool {
return ctx.Value(mapPassKey{}) == "before"
}
// IsAfterChildren is true within a Mutator when it is called after the children
// have been processed; however, this call is only made if the set of children
// changes since the Before call.
func IsAfterChildren(ctx context.Context) bool {
return ctx.Value(mapPassKey{}) == "after"
}
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