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refactor: extract function to write referrer attestations #4357

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merged 2 commits into from
Aug 29, 2025
Merged

refactor: extract function to write referrer attestations #4357

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980db77
refactor: extract function to write referrer attestations
arewm Aug 22, 2025
5057202
test: add test coverage for WriteReferrer functions
arewm Aug 27, 2025
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11 changes: 7 additions & 4 deletions pkg/oci/remote/remote.go
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Original file line number Diff line number Diff line change
Expand Up @@ -33,10 +33,13 @@ import (

// These enable mocking for unit testing without faking an entire registry.
var (
remoteImage = remote.Image
remoteIndex = remote.Index
remoteGet = remote.Get
remoteWrite = remote.Write
remoteImage = remote.Image
remoteIndex = remote.Index
remoteGet = remote.Get
remoteWrite = remote.Write
remoteHead = remote.Head
remoteWriteLayer = remote.WriteLayer
remotePut = remote.Put
)

// EntityNotFoundError is the error that SignedEntity returns when the
Expand Down
125 changes: 82 additions & 43 deletions pkg/oci/remote/write.go
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Original file line number Diff line number Diff line change
Expand Up @@ -146,7 +146,7 @@ func WriteSignaturesExperimentalOCI(d name.Digest, se oci.SignedEntity, opts ...
if err != nil {
return err
}
desc, err := remote.Head(ref, o.ROpt...)
desc, err := remoteHead(ref, o.ROpt...)
if err != nil {
return err
}
Expand All @@ -161,7 +161,7 @@ func WriteSignaturesExperimentalOCI(d name.Digest, se oci.SignedEntity, opts ...
return err
}
for _, v := range s {
if err := remote.WriteLayer(d.Repository, v, o.ROpt...); err != nil {
if err := remoteWriteLayer(d.Repository, v, o.ROpt...); err != nil {
return err
}
}
Expand All @@ -176,7 +176,7 @@ func WriteSignaturesExperimentalOCI(d name.Digest, se oci.SignedEntity, opts ...
return err
}
configLayer := static.NewLayer(configBytes, configDesc.MediaType)
if err := remote.WriteLayer(d.Repository, configLayer, o.ROpt...); err != nil {
if err := remoteWriteLayer(d.Repository, configLayer, o.ROpt...); err != nil {
return err
}

Expand Down Expand Up @@ -208,7 +208,7 @@ func WriteSignaturesExperimentalOCI(d name.Digest, se oci.SignedEntity, opts ...
// TODO: use ui.Infof
fmt.Fprintf(os.Stderr, "Uploading signature for [%s] to [%s] with config.mediaType [%s] layers[0].mediaType [%s].\n",
d.String(), targetRef.String(), artifactType, ctypes.SimpleSigningMediaType)
return remote.Put(targetRef, &taggableManifest{raw: b, mediaType: m.MediaType}, o.ROpt...)
return remotePut(targetRef, &taggableManifest{raw: b, mediaType: m.MediaType}, o.ROpt...)
}

type taggableManifest struct {
Expand All @@ -224,15 +224,17 @@ func (taggable taggableManifest) MediaType() (types.MediaType, error) {
return taggable.mediaType, nil
}

func WriteAttestationNewBundleFormat(d name.Digest, bundleBytes []byte, predicateType string, opts ...Option) error {
// WriteReferrer writes a referrer manifest for a given subject digest.
// It uploads the provided layers and creates a manifest that refers to the subject.
func WriteReferrer(d name.Digest, artifactType string, layers []v1.Layer, annotations map[string]string, opts ...Option) error {
o := makeOptions(d.Repository, opts...)

signTarget := d.String()
ref, err := name.ParseReference(signTarget, o.NameOpts...)
if err != nil {
return err
}
desc, err := remote.Head(ref, o.ROpt...)
desc, err := remoteHead(ref, o.ROpt...)
if err != nil {
return err
}
Expand All @@ -247,32 +249,35 @@ func WriteAttestationNewBundleFormat(d name.Digest, bundleBytes []byte, predicat
if err != nil {
return fmt.Errorf("failed to calculate size: %w", err)
}
err = remote.WriteLayer(d.Repository, configLayer, o.ROpt...)
err = remoteWriteLayer(d.Repository, configLayer, o.ROpt...)
if err != nil {
return fmt.Errorf("failed to upload layer: %w", err)
}

// generate bundle media type string
bundleMediaType, err := sgbundle.MediaTypeString("0.3")
if err != nil {
return fmt.Errorf("failed to generate bundle media type string: %w", err)
}

// Write the bundle layer
layer := static.NewLayer(bundleBytes, types.MediaType(bundleMediaType))
blobDigest, err := layer.Digest()
if err != nil {
return fmt.Errorf("failed to calculate digest: %w", err)
}

blobSize, err := layer.Size()
if err != nil {
return fmt.Errorf("failed to calculate size: %w", err)
}
layerDescriptors := make([]v1.Descriptor, len(layers))
for i, layer := range layers {
mediaType, err := layer.MediaType()
if err != nil {
return fmt.Errorf("failed to get media type: %w", err)
}
layerDigest, err := layer.Digest()
if err != nil {
return fmt.Errorf("failed to calculate digest: %w", err)
}
layerSize, err := layer.Size()
if err != nil {
return fmt.Errorf("failed to calculate size: %w", err)
}

err = remote.WriteLayer(d.Repository, layer, o.ROpt...)
if err != nil {
return fmt.Errorf("failed to upload layer: %w", err)
err = remoteWriteLayer(d.Repository, layer, o.ROpt...)
if err != nil {
return fmt.Errorf("failed to upload layer: %w", err)
}
layerDescriptors[i] = v1.Descriptor{
MediaType: mediaType,
Digest: layerDigest,
Size: layerSize,
}
}

// Create a manifest that includes the blob as a layer
Expand All @@ -281,42 +286,76 @@ func WriteAttestationNewBundleFormat(d name.Digest, bundleBytes []byte, predicat
MediaType: types.OCIManifestSchema1,
Config: v1.Descriptor{
MediaType: types.MediaType("application/vnd.oci.empty.v1+json"),
ArtifactType: bundleMediaType,
ArtifactType: artifactType,
Digest: configDigest,
Size: configSize,
},
Layers: []v1.Descriptor{
{
MediaType: types.MediaType(bundleMediaType),
Digest: blobDigest,
Size: blobSize,
},
},
Layers: layerDescriptors,
Subject: &v1.Descriptor{
MediaType: desc.MediaType,
Digest: desc.Digest,
Size: desc.Size,
},
Annotations: map[string]string{
"org.opencontainers.image.created": time.Now().UTC().Format(time.RFC3339),
"dev.sigstore.bundle.content": "dsse-envelope",
"dev.sigstore.bundle.predicateType": predicateType,
},
}, bundleMediaType}
Annotations: annotations,
}, artifactType}

targetRef, err := manifest.targetRef(d.Repository)
if err != nil {
return fmt.Errorf("failed to create target reference: %w", err)
}

if err := remote.Put(targetRef, manifest, o.ROpt...); err != nil {
if err := remotePut(targetRef, manifest, o.ROpt...); err != nil {
return fmt.Errorf("failed to upload manifest: %w", err)
}

return nil
}

// referrerManifest implements Taggable for use in remote.Put.
func WriteAttestationNewBundleFormat(d name.Digest, bundleBytes []byte, predicateType string, opts ...Option) error {
// generate bundle media type string
bundleMediaType, err := sgbundle.MediaTypeString("0.3")
if err != nil {
return fmt.Errorf("failed to generate bundle media type string: %w", err)
}

// Write the bundle layer
layer := static.NewLayer(bundleBytes, types.MediaType(bundleMediaType))

annotations := map[string]string{
"org.opencontainers.image.created": time.Now().UTC().Format(time.RFC3339),
"dev.sigstore.bundle.content": "dsse-envelope",
"dev.sigstore.bundle.predicateType": predicateType,
}

return WriteReferrer(d, bundleMediaType, []v1.Layer{layer}, annotations, opts...)
}

// WriteAttestationsReferrer publishes the attestations attached to the given entity
// into the provided repository using the referrers API.
func WriteAttestationsReferrer(d name.Digest, se oci.SignedEntity, opts ...Option) error {
atts, err := se.Attestations()
if err != nil {
return err
}
layers, err := atts.Layers()
if err != nil {
return err
}

annotations := map[string]string{
"org.opencontainers.image.created": time.Now().UTC().Format(time.RFC3339),
}

// We have to pick an artifactType for the referrer manifest. The attestation
// layers themselves are DSSE envelopes, which wrap in-toto statements.
// For discovery, the artifactType should describe the semantic content (the
// in-toto statement) rather than the wrapper format (the DSSE envelope).
// Using the in-toto media type is the most appropriate and conventional choice,
// as policy engines and other tools will query for attestations using this type.
Comment on lines +349 to +354
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@steiza steiza Aug 26, 2025

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I had to really think through this (mostly because as mentioned I haven't spent much time with cosign's OCI functions), but I think this is the right answer.

Retrieving an attestation that doesn't use the new protobuf bundles:

$ go run cmd/cosign/main.go download attestation ghcr.io/steiza/actions-oidc-proxy:v1 | jq
{
  "payloadType": "application/vnd.in-toto+json",
  "payload": "eyJfdHlwZSI6Imh0dHBzOi8vaW4tdG90by5pby9TdGF0ZW1lbnQvdjAuMSIsInByZWRpY2F0ZVR5cGUiOiJodHRwczovL2Nvc2lnbi5zaWdzdG9yZS5kZXYvYXR0ZXN0YXRpb24vdjEiLCJzdWJqZWN0IjpbeyJuYW1lIjoiZ2hjci5pby9zdGVpemEvYWN0aW9ucy1vaWRjLXByb3h5IiwiZGlnZXN0Ijp7InNoYTI1NiI6ImEwNGMyOTk2YzRjNDJhYTUxNzQ5MmJjMGQ4ZTA5Y2EwMDJhNTk5ZDEyZjVlODJiZDUzNzNlZDYzMTNhZjZhNzkifX1dLCJwcmVkaWNhdGUiOnsiRGF0YSI6IntcInBhc3NlZFwiOiB0cnVlfVxuIiwiVGltZXN0YW1wIjoiMjAyNS0wOC0xNVQxODoyMjoyMVoifX0=",
  "signatures": [
    {
      "keyid": "",
      "sig": "MEYCIQD+TJnd3/GuORNfKMMpbviudNGyy+G9qUw0nOtQABEEnAIhAKiTsFRVWdPRSVN/xD3LxGkb/5xPz4f8voN6e16jdePa"
    }
  ]
}

application/vnd.in-toto+json makes sense!

return WriteReferrer(d, ctypes.IntotoPayloadType, layers, annotations, opts...)
}

// referrerManifest implements Taggable for use in remotePut.
// This type also augments the built-in v1.Manifest with an ArtifactType field
// which is part of the OCI 1.1 Image Manifest spec but is unsupported by
// go-containerregistry at this time.
Expand Down
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