@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(parent_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 1, parent_);
    }
    if (pageSize_ != 0) {
      output.writeInt32(2, pageSize_);
    }
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(pageToken_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 3, pageToken_);
    }
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(filter_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 6, filter_);
    }
    getUnknownFields().writeTo(output);
  }
<pre>
A filter expression that matches resources returned in the response.
Currently, only filtering on the `direction` field is supported. To return
routes imported from the peer network, provide "direction=INCOMING". To
return routes exported from the VMware Engine network, provide
"direction=OUTGOING". Other filter expressions return an error.
</pre>

<code>string filter = 6;</code>

@return The bytes for filter.
java-vmwareengine/proto-google-cloud-vmwareengine-v1/src/main/java/com/google/cloud/vmwareengine/v1/ListPeeringRoutesRequest.java