Chris Egerton created KAFKA-8407:
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Summary: Connector client overrides broken on client configs with
type 'Class'
Key: KAFKA-8407
URL: https://issues.apache.org/jira/browse/KAFKA-8407
Project: Kafka
Issue Type: Bug
Components: KafkaConnect
Affects Versions: 2.3.0
Reporter: Chris Egerton
Assignee: Chris Egerton
When a connector request is submitted that overrides a client configuration
that is meant to contain the name of a class (such as
{{sasl.login.callback.handler.class}}), a 500 response is generated and the
following stack trace can be found in the logs for Connect:
{quote}[2019-05-22 14:51:36,123] ERROR Uncaught exception in REST call to
/connectors
(org.apache.kafka.connect.runtime.rest.errors.ConnectExceptionMapper:61)
java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Class
at org.apache.kafka.common.config.ConfigDef.convertToString(ConfigDef.java:774)
at
org.apache.kafka.connect.runtime.AbstractHerder.convertConfigValue(AbstractHerder.java:491)
at
org.apache.kafka.connect.runtime.AbstractHerder.validateClientOverrides(AbstractHerder.java:426)
at
org.apache.kafka.connect.runtime.AbstractHerder.validateConnectorConfig(AbstractHerder.java:342)
at
org.apache.kafka.connect.runtime.distributed.DistributedHerder$6.call(DistributedHerder.java:565)
at
org.apache.kafka.connect.runtime.distributed.DistributedHerder$6.call(DistributedHerder.java:562)
at
org.apache.kafka.connect.runtime.distributed.DistributedHerder.tick(DistributedHerder.java:292)
at
org.apache.kafka.connect.runtime.distributed.DistributedHerder.run(DistributedHerder.java:241)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
{quote}
This appears to be limited only to client configs that are meant to be classes
due to the fact that {{ConfigDef.convertToString(...)}} assumes its first
argument is an instance of {{Class<?>}} when its second argument is
{{ConfigDef.Type.CLASS}} and then casts accordingly. If the second argument is
anything else (besides {{ConfigDef.Type.LIST}}, which is handled separately by
the {{AbstractHerder}} during client override validation), then {{toString()}}
is invoked on it without any casting, avoiding any problems.
The cause of this is due to the fact that the newly-introduced
{{ConnectorClientConfigOverridePolicy}} interface returns a list of
{{ConfigValue}} instances for its validation. The {{value()}} for each of these
can be any type, although with the default implementations available ({{All}},
{{None}}, {{Principal}}) if one is returned at all it's just the same type of
what was passed in for that particular config. In the case of the
{{AbstractHerder.validateClientOverrides(...)}} method, the raw strings for the
client configs are used. However, the
{{AbstractHerder.convertConfigValue(...)}} is then called for those raw strings
but with the {{ConfigDef.Type}} of the config based on the relevant client
{{ConfigDef}} (i.e., {{ProducerConfig.configDef()}},
{{ConsumerConfig.configDef()}}, or {{AdminClientConfig.configDef()}}). This in
turn can and will result in {{ConfigDef.convertToString(someClassNameAsAString,
ConfigDef.Type.CLASS)}} being invoked.
Although this isn't technically a comprehensive fix, a quick option would be to
invoke {{ConfigDef.parse(...)}} using the relevant client {{ConfigDef}} before
passing overrides to the policy. Technically, this would still lead to problems
if the policy decided to return just the name of a class for a config that of
type class instead, so we may want to investigate other options as well.
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