@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    if (sourceCase_ == 1) {
      output.writeBytes(1, (com.google.protobuf.ByteString) source_);
    }
    if (sourceCase_ == 2) {
      output.writeMessage(2, (com.google.cloud.translate.v3beta1.GcsSource) source_);
    }
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(mimeType_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 4, mimeType_);
    }
    getUnknownFields().writeTo(output);
  }
<pre>
Specifies the input document's mime_type.

If not specified it will be determined using the file extension for
gcs_source provided files. For a file provided through bytes content the
mime_type must be provided.
Currently supported mime types are:
- application/pdf
- application/vnd.openxmlformats-officedocument.wordprocessingml.document
- application/vnd.openxmlformats-officedocument.presentationml.presentation
- application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
</pre>

<code>string mime_type = 4;</code>

@return The bytes for mimeType.
java-translate/proto-google-cloud-translate-v3beta1/src/main/java/com/google/cloud/translate/v3beta1/DocumentInputConfig.java