Refactor cloudkms signer to return an error on the constructor.

kms/cloudkms/cloudkms.go

@@ -140,19 +140,7 @@ func (k *CloudKMS) CreateSigner(req *apiv1.CreateSignerRequest) (crypto.Signer,
 	if req.SigningKey == "" {
 		return nil, errors.New("signing key cannot be empty")
 	}
-
+	return NewSigner(k.client, req.SigningKey)
-	// Validate that the key exists
-	ctx, cancel := defaultContext()
-	defer cancel()
-
-	_, err := k.client.GetPublicKey(ctx, &kmspb.GetPublicKeyRequest{
-		Name: req.SigningKey,
-	})
-	if err != nil {
-		return nil, errors.Wrap(err, "cloudKMS GetPublicKey failed")
-	}
-
-	return NewSigner(k.client, req.SigningKey), nil
 }
 
 // CreateKey creates in Google's Cloud KMS a new asymmetric key for signing.

kms/cloudkms/cloudkms_test.go

@@ -165,6 +165,15 @@ func TestCloudKMS_Close(t *testing.T) {
 
 func TestCloudKMS_CreateSigner(t *testing.T) {
 	keyName := "projects/p/locations/l/keyRings/k/cryptoKeys/c/cryptoKeyVersions/1"
+	pemBytes, err := ioutil.ReadFile("testdata/pub.pem")
+	if err != nil {
+		t.Fatal(err)
+	}
+	pk, err := pemutil.ParseKey(pemBytes)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	type fields struct {
 		client KeyManagementClient
 	}
@@ -178,8 +187,16 @@ func TestCloudKMS_CreateSigner(t *testing.T) {
 		want    crypto.Signer
 		wantErr bool
 	}{
-		{"ok", fields{&MockClient{}}, args{&apiv1.CreateSignerRequest{SigningKey: keyName}}, &Signer{client: &MockClient{}, signingKey: keyName}, false},
+		{"ok", fields{&MockClient{
-		{"fail", fields{&MockClient{}}, args{&apiv1.CreateSignerRequest{SigningKey: ""}}, nil, true},
+			getPublicKey: func(_ context.Context, _ *kmspb.GetPublicKeyRequest, _ ...gax.CallOption) (*kmspb.PublicKey, error) {
+				return &kmspb.PublicKey{Pem: string(pemBytes)}, nil
+			},
+		}}, args{&apiv1.CreateSignerRequest{SigningKey: keyName}}, &Signer{client: &MockClient{}, signingKey: keyName, publicKey: pk}, false},
+		{"fail", fields{&MockClient{
+			getPublicKey: func(_ context.Context, _ *kmspb.GetPublicKeyRequest, _ ...gax.CallOption) (*kmspb.PublicKey, error) {
+				return nil, fmt.Errorf("test error")
+			},
+		}}, args{&apiv1.CreateSignerRequest{SigningKey: ""}}, nil, true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -191,6 +208,9 @@ func TestCloudKMS_CreateSigner(t *testing.T) {
 				t.Errorf("CloudKMS.CreateSigner() error = %v, wantErr %v", err, tt.wantErr)
 				return
 			}
+			if signer, ok := got.(*Signer); ok {
+				signer.client = &MockClient{}
+			}
 			if !reflect.DeepEqual(got, tt.want) {
 				t.Errorf("CloudKMS.CreateSigner() = %v, want %v", got, tt.want)
 			}

kms/cloudkms/signer.go

@@ -13,33 +13,41 @@ import (
 type Signer struct {
 	client     KeyManagementClient
 	signingKey string
+	publicKey  crypto.PublicKey
 }
 
-func NewSigner(c KeyManagementClient, signingKey string) *Signer {
+// NewSigner creates a new crypto.Signer the given CloudKMS signing key.
-	return &Signer{
+func NewSigner(c KeyManagementClient, signingKey string) (*Signer, error) {
+	// Make sure that the key exists.
+	signer := &Signer{
 		client:     c,
 		signingKey: signingKey,
 	}
+	if err := signer.preloadKey(signingKey); err != nil {
+		return nil, err
+	}
+
+	return signer, nil
 }
 
-// Public returns the public key of this signer or an error.
+func (s *Signer) preloadKey(signingKey string) error {
-func (s *Signer) Public() crypto.PublicKey {
 	ctx, cancel := defaultContext()
 	defer cancel()
 
 	response, err := s.client.GetPublicKey(ctx, &kmspb.GetPublicKeyRequest{
-		Name: s.signingKey,
+		Name: signingKey,
 	})
 	if err != nil {
 		return errors.Wrap(err, "cloudKMS GetPublicKey failed")
 	}
 
-	pk, err := pemutil.ParseKey([]byte(response.Pem))
+	s.publicKey, err = pemutil.ParseKey([]byte(response.Pem))
-	if err != nil {
 	return err
-	}
+}
 
-	return pk
+// Public returns the public key of this signer or an error.
+func (s *Signer) Public() crypto.PublicKey {
+	return s.publicKey
 }
 
 // Sign signs digest with the private key stored in Google's Cloud KMS.

kms/cloudkms/signer_test.go

@@ -16,6 +16,15 @@ import (
 )
 
 func Test_newSigner(t *testing.T) {
+	pemBytes, err := ioutil.ReadFile("testdata/pub.pem")
+	if err != nil {
+		t.Fatal(err)
+	}
+	pk, err := pemutil.ParseKey(pemBytes)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	type args struct {
 		c          KeyManagementClient
 		signingKey string
@@ -24,22 +33,42 @@ func Test_newSigner(t *testing.T) {
 		name    string
 		args    args
 		want    *Signer
+		wantErr bool
 	}{
-		{"ok", args{&MockClient{}, "signingKey"}, &Signer{client: &MockClient{}, signingKey: "signingKey"}},
+		{"ok", args{&MockClient{
+			getPublicKey: func(_ context.Context, _ *kmspb.GetPublicKeyRequest, _ ...gax.CallOption) (*kmspb.PublicKey, error) {
+				return &kmspb.PublicKey{Pem: string(pemBytes)}, nil
+			},
+		}, "signingKey"}, &Signer{client: &MockClient{}, signingKey: "signingKey", publicKey: pk}, false},
+		{"fail get public key", args{&MockClient{
+			getPublicKey: func(_ context.Context, _ *kmspb.GetPublicKeyRequest, _ ...gax.CallOption) (*kmspb.PublicKey, error) {
+				return nil, fmt.Errorf("an error")
+			},
+		}, "signingKey"}, nil, true},
+		{"fail parse pem", args{&MockClient{
+			getPublicKey: func(_ context.Context, _ *kmspb.GetPublicKeyRequest, _ ...gax.CallOption) (*kmspb.PublicKey, error) {
+				return &kmspb.PublicKey{Pem: string("bad pem")}, nil
+			},
+		}, "signingKey"}, nil, true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			if got := NewSigner(tt.args.c, tt.args.signingKey); !reflect.DeepEqual(got, tt.want) {
+			got, err := NewSigner(tt.args.c, tt.args.signingKey)
-				t.Errorf("newSigner() = %v, want %v", got, tt.want)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("NewSigner() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != nil {
+				got.client = &MockClient{}
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("NewSigner() = %v, want %v", got, tt.want)
 			}
 		})
 	}
 }
 
 func Test_signer_Public(t *testing.T) {
-	keyName := "projects/p/locations/l/keyRings/k/cryptoKeys/c/cryptoKeyVersions/1"
-	testError := fmt.Errorf("an error")
-
 	pemBytes, err := ioutil.ReadFile("testdata/pub.pem")
 	if err != nil {
 		t.Fatal(err)
@@ -52,42 +81,23 @@ func Test_signer_Public(t *testing.T) {
 	type fields struct {
 		client     KeyManagementClient
 		signingKey string
+		publicKey  crypto.PublicKey
 	}
 	tests := []struct {
 		name   string
 		fields fields
 		want   crypto.PublicKey
-		wantErr bool
 	}{
-		{"ok", fields{&MockClient{
+		{"ok", fields{&MockClient{}, "signingKey", pk}, pk},
-			getPublicKey: func(_ context.Context, _ *kmspb.GetPublicKeyRequest, _ ...gax.CallOption) (*kmspb.PublicKey, error) {
-				return &kmspb.PublicKey{Pem: string(pemBytes)}, nil
-			},
-		}, keyName}, pk, false},
-		{"fail get public key", fields{&MockClient{
-			getPublicKey: func(_ context.Context, _ *kmspb.GetPublicKeyRequest, _ ...gax.CallOption) (*kmspb.PublicKey, error) {
-				return nil, testError
-			},
-		}, keyName}, nil, true},
-		{"fail parse pem", fields{
-			&MockClient{
-				getPublicKey: func(_ context.Context, _ *kmspb.GetPublicKeyRequest, _ ...gax.CallOption) (*kmspb.PublicKey, error) {
-					return &kmspb.PublicKey{Pem: string("bad pem")}, nil
-				},
-			}, keyName}, nil, true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			s := &Signer{
 				client:     tt.fields.client,
 				signingKey: tt.fields.signingKey,
+				publicKey:  tt.fields.publicKey,
 			}
-			got := s.Public()
+			if got := s.Public(); !reflect.DeepEqual(got, tt.want) {
-			if _, ok := got.(error); ok != tt.wantErr {
-				t.Errorf("signer.Public() error = %v, wantErr %v", got, tt.wantErr)
-				return
-			}
-			if !tt.wantErr && !reflect.DeepEqual(got, tt.want) {
 				t.Errorf("signer.Public() = %v, want %v", got, tt.want)
 			}
 		})