ociclient: require digests for descriptors

In PR #29, I suggested that we should verify that the
tests fail when the fix was not applied, but the tests
did not fail in that case.

It turns out that's because the client was being a bit
too slack about requiring digests in responses, meaning
that the client succeeded even when it should have failed.

This change makes `ociclient.descriptorFromResponse`
a little more stringent about digests, and I've explicitly
verified that when the changes in #29 are reverted,
the tests do in fact fail as expected.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: Ic7352b572593a60dc2209193fdd64bf2e4235af9
Dispatch-Trailer: {"type":"trybot","CL":1191111,"patchset":4,"ref":"refs/changes/11/1191111/4","targetBranch":"main"}

ociregistry/ociclient/client.go

@@ -124,18 +124,25 @@ type client struct {
 	listPageSize int
 }
 
+type descriptorRequired byte
+
+const (
+	requireSize descriptorRequired = 1 << iota
+	requireDigest
+)
+
 // descriptorFromResponse tries to form a descriptor from an HTTP response,
 // filling in the Digest field using knownDigest if it's not present.
 //
 // Note: this implies that the Digest field will be empty if there is no
 // digest in the response and knownDigest is empty.
-func descriptorFromResponse(resp *http.Response, knownDigest digest.Digest, requireSize bool) (ociregistry.Descriptor, error) {
+func descriptorFromResponse(resp *http.Response, knownDigest digest.Digest, require descriptorRequired) (ociregistry.Descriptor, error) {
 	contentType := resp.Header.Get("Content-Type")
 	if contentType == "" {
 		contentType = "application/octet-stream"
 	}
 	size := int64(0)
-	if requireSize {
+	if (require & requireSize) != 0 {
 		if resp.StatusCode == http.StatusPartialContent {
 			contentRange := resp.Header.Get("Content-Range")
 			if contentRange == "" {
@@ -165,6 +172,9 @@ func descriptorFromResponse(resp *http.Response, knownDigest digest.Digest, requ
 	} else {
 		digest = knownDigest
 	}
+	if (require&requireDigest) != 0 && digest == "" {
+		return ociregistry.Descriptor{}, fmt.Errorf("no digest found in response")
+	}
 	return ociregistry.Descriptor{
 		Digest:    digest,
 		MediaType: contentType,

ociregistry/ociclient/reader.go

@@ -60,7 +60,7 @@ func (c *client) GetBlobRange(ctx context.Context, repo string, digest ociregist
 	// Fix that either by returning ErrUnsupported or by reading the whole
 	// blob and returning only the required portion.
 	defer closeOnError(&_err, resp.Body)
-	desc, err := descriptorFromResponse(resp, ociregistry.Digest(rreq.Digest), true)
+	desc, err := descriptorFromResponse(resp, ociregistry.Digest(rreq.Digest), requireSize)
 	if err != nil {
 		return nil, fmt.Errorf("invalid descriptor in response: %v", err)
 	}
@@ -97,7 +97,7 @@ func (c *client) resolve(ctx context.Context, rreq *ocirequest.Request) (ociregi
 		return ociregistry.Descriptor{}, err
 	}
 	resp.Body.Close()
-	desc, err := descriptorFromResponse(resp, ociregistry.Digest(rreq.Digest), true)
+	desc, err := descriptorFromResponse(resp, ociregistry.Digest(rreq.Digest), requireSize|requireDigest)
 	if err != nil {
 		return ociregistry.Descriptor{}, fmt.Errorf("invalid descriptor in response: %v", err)
 	}
@@ -138,7 +138,7 @@ func (c *client) read(ctx context.Context, rreq *ocirequest.Request) (_ ociregis
 		return nil, err
 	}
 	defer closeOnError(&_err, resp.Body)
-	desc, err := descriptorFromResponse(resp, ociregistry.Digest(rreq.Digest), true)
+	desc, err := descriptorFromResponse(resp, ociregistry.Digest(rreq.Digest), requireSize)
 	if err != nil {
 		return nil, fmt.Errorf("invalid descriptor in response: %v", err)
 	}
@@ -176,13 +176,10 @@ func (c *client) read(ctx context.Context, rreq *ocirequest.Request) (_ ociregis
 				return nil, err
 			}
 			resp1.Body.Close()
-			desc, err = descriptorFromResponse(resp1, ociregistry.Digest(rreq1.Digest), true)
+			desc, err = descriptorFromResponse(resp1, ociregistry.Digest(rreq1.Digest), requireSize|requireDigest)
 			if err != nil {
 				return nil, err
 			}
-			if desc.Digest == "" {
-				return nil, fmt.Errorf("no digest header found in response")
-			}
 		}
 	}
 	return newBlobReader(resp.Body, desc), nil

ociregistry/ociclient/writer.go

@@ -82,7 +82,8 @@ func (c *client) MountBlob(ctx context.Context, fromRepo, toRepo string, dig oci
 		// return Unsupported.
 		return ociregistry.Descriptor{}, fmt.Errorf("registry does not support mounts: %w", ociregistry.ErrUnsupported)
 	}
-	return descriptorFromResponse(resp, dig, false)
+	// TODO: is it OK to omit the size from the returned descriptor here?
+	return descriptorFromResponse(resp, dig, requireDigest)
 }
 
 func (c *client) PushBlob(ctx context.Context, repo string, desc ociregistry.Descriptor, r io.Reader) (_ ociregistry.Descriptor, _err error) {