Couchbase - Kafka - Logstash output invalid characters

[jscubida (J C)]

Hi. I currently have the following setup:

• Confluent Open Source 4.1.0 (which includes Kafka)
• Couchbase 4.5.1-2844 Community Edition (build-2844)
• Logstash 6.2.4

Data flows from Couchbase -> Kafka -> Logstash. According to the Kafka logs, it receives the following from Couchbase:

{"event":"mutation","partition":520,"key":"_sync:seq","cas":1527802622171611136,"bySeqno":25188,"revSeqno":339050,"expiration":{"int":0},"flags":{"int":0},"lockTime":{"int":0},"content":{"bytes":"355496"}}

When Logstash receives this message, the log outputs the following:

{
   "message" => "\u0000\u0000\u0000\u0000\u0002\u0010mutation�\b\u0012_sync:seq�������*ȉ\u0003Ա)\u0002\u0000\u0002\u0000\u0002\u0000\u0002\f355496",
  "@version" => "1",
"@timestamp" => 2018-05-31T21:37:02.284Z
}

Here is my Logstash config:

input {
    kafka {
        bootstrap_servers => "<myserver>:9092"
        topics => ["test-default"] 
    }
}

output {
    stdout { }
}

Here's my couchbase.properties file for Kafka:

name=testy-couchbase
connector.class=com.couchbase.connect.kafka.CouchbaseSourceConnector
tasks.max=2
connection.cluster_address=<myserver>
connection.bucket=pa_test
connection.timeout.ms=2000
topic.name=test-default
use_snapshots=false

What could be causing the invalid characters in Logstash? How could I go about debugging this?

Thanks!