func (af *GCSArtifactFetcher) artifact(key string, artifactName string, sizeLimit int64) (lenses.Artifact, error) {
	src, err := newGCSJobSource(key)
	if err != nil {
		return nil, fmt.Errorf("Failed to get GCS job source from %s: %v", key, err)
	}

	bucketName, prefix := extractBucketPrefixPair(src.jobPath())
	bkt := af.client.Bucket(bucketName)
	obj := &gcsArtifactHandle{bkt.Object(path.Join(prefix, artifactName))}
	artifactLink := &url.URL{
		Scheme: httpsScheme,
		Host:   "storage.googleapis.com",
		Path:   path.Join(src.jobPath(), artifactName),
	}
	return NewGCSArtifact(context.Background(), obj, artifactLink.String(), artifactName, sizeLimit), nil
}
func (af *GCSArtifactFetcher) artifact(key string, artifactName string, sizeLimit int64) (lenses.Artifact, error) {
	src, err := newGCSJobSource(key)
	if err != nil {
		return nil, fmt.Errorf("Failed to get GCS job source from %s: %v", key, err)
	}

	bucketName, prefix := extractBucketPrefixPair(src.jobPath())
	bkt := af.client.Bucket(bucketName)
	obj := &gcsArtifactHandle{bkt.Object(path.Join(prefix, artifactName))}
	artifactLink := &url.URL{
		Scheme: httpsScheme,
		Host:   "storage.googleapis.com",
		Path:   path.Join(src.jobPath(), artifactName),
	}
	return NewGCSArtifact(context.Background(), obj, artifactLink.String(), artifactName, sizeLimit), nil
}
// Artifact constructs a GCS artifact from the given GCS bucket and key. Uses the golang GCS library
// to get read handles. If the artifactName is not a valid key in the bucket a handle will still be
// constructed and returned, but all read operations will fail (dictated by behavior of golang GCS lib).