feat: new S3 method to check if key exists (#116)

* new KeyExists() method

Signed-off-by: Julie Vogelman <[email protected]>

* fix: KeyExists() to handle errors correctly

Signed-off-by: Julie Vogelman <[email protected]>

* fix: include stack in error, for consistency with other errors

Signed-off-by: Julie Vogelman <[email protected]>

s3/s3.go

@@ -37,6 +37,10 @@ type S3Client interface {
 	// OpenFile opens a file for much lower disk and memory usage that GetFile
 	OpenFile(bucket, key string) (io.ReadCloser, error)
 
+	// KeyExists checks if object exists (and if we have permission to access)
+	KeyExists(bucket, key string) (bool, error)
+
+	// Delete deletes the key from the bucket
 	Delete(bucket, key string) error
 
 	// GetDirectory downloads a directory to a local file path
@@ -45,7 +49,7 @@ type S3Client interface {
 	// ListDirectory list the contents of a directory/bucket
 	ListDirectory(bucket, keyPrefix string) ([]string, error)
 
-	// IsDirectory tests if the key is acting like a s3 directory
+	// IsDirectory tests if the key is acting like an s3 directory
 	IsDirectory(bucket, key string) (bool, error)
 
 	// BucketExists returns whether a bucket exists
@@ -279,6 +283,26 @@ func (s *s3client) OpenFile(bucket, key string) (io.ReadCloser, error) {
 	return f, nil
 }
 
+// checks if object exists (and if we have permission to access)
+func (s *s3client) KeyExists(bucket, key string) (bool, error) {
+	log.WithFields(log.Fields{"endpoint": s.Endpoint, "bucket": bucket, "key": key}).Info("Checking key exists from s3")
+
+	encOpts, err := s.EncryptOpts.buildServerSideEnc(bucket, key)
+	if err != nil {
+		return false, errors.WithStack(err)
+	}
+
+	_, err = s.minioClient.StatObject(s.ctx, bucket, key, minio.StatObjectOptions{ServerSideEncryption: encOpts})
+	if err == nil {
+		return true, nil
+	}
+	if IsS3ErrCode(err, "NoSuchKey") {
+		return false, nil
+	}
+
+	return false, errors.WithStack(err)
+}
+
 func (s *s3client) Delete(bucket, key string) error {
 	log.WithFields(log.Fields{"endpoint": s.Endpoint, "bucket": bucket, "key": key}).Info("Deleting object from s3")
 	return s.minioClient.RemoveObject(s.ctx, bucket, key, minio.RemoveObjectOptions{})