private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.visionai.v1.RequestMetadata,
            com.google.cloud.visionai.v1.RequestMetadata.Builder,
            com.google.cloud.visionai.v1.RequestMetadataOrBuilder>
        getMetadataFieldBuilder() {
      if (metadataBuilder_ == null) {
        if (!(requestCase_ == 2)) {
          request_ = com.google.cloud.visionai.v1.RequestMetadata.getDefaultInstance();
        }
        metadataBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.visionai.v1.RequestMetadata,
                com.google.cloud.visionai.v1.RequestMetadata.Builder,
                com.google.cloud.visionai.v1.RequestMetadataOrBuilder>(
                (com.google.cloud.visionai.v1.RequestMetadata) request_,
                getParentForChildren(),
                isClean());
        request_ = null;
      }
      requestCase_ = 2;
      onChanged();
      return metadataBuilder_;
    }
<pre>
The first message of the streaming rpc including the request metadata.
</pre>

<code>.google.cloud.visionai.v1.RequestMetadata metadata = 2;</code>
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/SendPacketsRequest.java