Fix ObjectExistsWithSize s3 implementation.

- We're not correctly returning the size of the file when there's no error

pkg/storage/chunk/client/aws/s3_storage_client.go

@@ -338,7 +338,7 @@ func (a *S3ObjectClient) ObjectExistsWithSize(ctx context.Context, objectKey str
 			return nil
 		})
 		if lastErr == nil {
-			return true, 0, nil
+			return true, objectSize, nil
 		}
 
 		if a.IsObjectNotFoundErr(lastErr) {
@@ -348,11 +348,7 @@ func (a *S3ObjectClient) ObjectExistsWithSize(ctx context.Context, objectKey str
 		retries.Wait()
 	}
 
-	if lastErr != nil {
-		return false, 0, lastErr
-	}
-
-	return true, objectSize, nil
+	return false, 0, lastErr
 }
 
 // DeleteObject deletes the specified objectKey from the appropriate S3 bucket

pkg/storage/chunk/client/aws/s3_storage_client_test.go

@@ -309,6 +309,38 @@ func (m *MockS3Client) HeadObject(input *s3.HeadObjectInput) (*s3.HeadObjectOutp
 	return m.HeadObjectFunc(input)
 }
 
+func Test_ExistsWithSize(t *testing.T) {
+	mockS3 := &MockS3Client{
+		HeadObjectFunc: func(_ *s3.HeadObjectInput) (*s3.HeadObjectOutput, error) {
+			var size int64
+			size = 128
+			return &s3.HeadObjectOutput{ContentLength: &size}, nil
+		},
+	}
+
+	c, err := NewS3ObjectClient(S3Config{
+		AccessKeyID:     "foo",
+		SecretAccessKey: flagext.SecretWithValue("bar"),
+		BackoffConfig:   backoff.Config{MaxRetries: 3},
+		BucketNames:     "foo",
+		Inject: func(_ http.RoundTripper) http.RoundTripper {
+			return RoundTripperFunc(func(_ *http.Request) (*http.Response, error) {
+				return &http.Response{
+					StatusCode: http.StatusOK,
+					Body:       io.NopCloser(bytes.NewReader([]byte("object content"))),
+				}, nil
+			})
+		},
+	}, hedging.Config{})
+	require.NoError(t, err)
+	c.S3 = mockS3
+
+	exists, size, err := c.ObjectExistsWithSize(context.Background(), "abc")
+	require.NoError(t, err)
+	require.EqualValues(t, 128, size)
+	require.True(t, exists)
+}
+
 func Test_RetryLogic(t *testing.T) {
 	for _, tc := range []struct {
 		name       string