@java.lang.Override
    public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
      if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(usage_)) {
        com.google.protobuf.GeneratedMessageV3.writeString(output, 2, usage_);
      }
      if (sourceCase_ == 3) {
        output.writeMessage(3, (com.google.cloud.translate.v3.GcsInputSource) source_);
      }
      getUnknownFields().writeTo(output);
    }
<pre>
Google Cloud Storage file source.
</pre>

<code>.google.cloud.translation.v3.GcsInputSource gcs_source = 3;</code>
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/DatasetInputConfig.java