SpliceBlob: check that the digest function is supported

Author: mostynb

server/grpc_cas.go

@@ -385,6 +385,19 @@ func (s *grpcServer) SpliceBlob(ctx context.Context, req *pb.SpliceBlobRequest)
 			"SpliceBlob called with nil SpliceBlobRequest")
 	}
 
+	if req.DigestFunction != pb.DigestFunction_UNKNOWN && req.DigestFunction != pb.DigestFunction_SHA256 {
+		digestName, ok := pb.DigestFunction_Value_name[int32(req.DigestFunction)]
+		if ok {
+			return nil, grpc_status.Errorf(codes.InvalidArgument,
+				"SpliceBlob called with unsupported digest function: %s", digestName)
+		}
+
+		return nil, grpc_status.Errorf(codes.InvalidArgument,
+			"SpliceBlob called with unrecognised digest function: %d", req.DigestFunction)
+	}
+
+	// From this point, we assume that the digest function is SHA256 and verify digests as necessary.
+
 	// Check that req.ChunkDigests is OK.
 
 	if len(req.ChunkDigests) == 0 {

server/grpc_cas_spliceblobs_test.go

@@ -419,3 +419,26 @@ func TestSpliceBlobWithMissingChunk(t *testing.T) {
 		t.Fatal("expected \"missing\" blob not to exist in the cache yet, but got error", err)
 	}
 }
+
+func TestUnsupportedSpliceBlobDigestsAreRejected(t *testing.T) {
+	fixture, helloDigest, worldDigest, helloworldDigest := spliceBlobTestSetup(t)
+	defer func() { _ = os.Remove(fixture.tempdir) }()
+
+	spliceReq := pb.SpliceBlobRequest{
+		BlobDigest: helloworldDigest,
+		ChunkDigests: []*pb.Digest{
+			helloDigest,
+			worldDigest,
+		},
+		DigestFunction: pb.DigestFunction_MD5, // Unsupported
+	}
+
+	_, err := fixture.casClient.SpliceBlob(ctx, &spliceReq)
+	if err == nil {
+		t.Fatal("expected error when specifying an unsupported SpliceBlobRequest.DigestFunction")
+	}
+
+	if status.Code(err) != codes.InvalidArgument {
+		t.Fatal("expected an InvalidArgument error, got:", err)
+	}
+}