THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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package org.apache.kafka.server;
/**
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*
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An
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interface
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for
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enforcing
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a
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policy
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on
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the
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records
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that
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are
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accepted
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by
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this
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*
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broker.
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*
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*
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A
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common
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use
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case
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is
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for
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validating
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that
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records
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contain
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the
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correct
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schema
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*
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information.
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*
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*
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If the broker config <code>record.validation.policy.class.
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name</code>
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is
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defined,
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Kafka
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will
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*
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create
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an
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instance
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of
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the
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specified
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class
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using
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the
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default
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constructor
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and
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*
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will
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then
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pass
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the
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broker
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configs
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to
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its
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<code>configure()</code>
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method.
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*
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During
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broker
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shutdown,
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the
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<code>close()</code>
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method
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will
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be
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invoked
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so
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*
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that
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resources
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can
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be
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released
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(if
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necessary). * * If the broker config <code>record.validation.policy.class.path</code> is defined, * the RecordValidationPolicy implementation and its dependent libraries will be loaded * by a dedicated classloader which searches this class path before the Kafka broker class path. * The syntax of this string parameter that of a Java class path. */
public interface RecordValidationPolicy extends Configurable, Closeable {
/**
* TopicMetadata describes the topic-partition a record is being produced to.
*/
public interface TopicMetadata {
TopicPartitionTopicIdPartition topicPartitiontopicIdPartition();
/**
* @return the value of the topic config <code>"record.validation.policy"</code>
*/
String validationPolicy();
}
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Importance: low
Update mode: read-only
record.validation.policy.class.pathAn optional Java class path for the RecordValidationPolicy implementation. If specified, the RecordValidationPolicy implementation and its dependent libraries will be loaded by a dedicated classloader which searches this class path before the Kafka broker class path. The syntax of this string parameter that of a Java class path.
Type: string
Default: null
Valid values:
Importance: low
Update mode: read-only
New Topic config
record.validation.policy
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We discarded the idea that the validation policy plugin class could be defined per-topic, as a single per-broker policy could act as a facade to different policies specific to topics (e.g. different registries)
We discarded the idea to add an optional filed (eg schema id) to the kafka protocol Produce API, as that would require new clients not just serdes. Moreover, KIP-467 makes this approach look unnecessary.
It remains possible to implement a Kafka Streams functionality that filters a topic that clients write to, into another topic with validated messages (and maybe a “dead letter” topic for invalid ones). Such an alternative approach doesn’t provide any direct feedback to the client producer in the response. It also doesn’t require the broker to execute third party code semantically coupled with the clients, at the price of having an extra “moving part” (the Streams app) which contains such logic. Moreover, the topic-to-schema mapping must map both input topic and destination topic to the same schema.
- We discarded having a boolean topic config to control per-topic enablement of the validation, when a policy is specified at the broker level, in favor of a string topic config whose value that can be consumed by the policy, as per the sample below.
Sample test policy
Here is a sample of a validation policy that we may use for the unit tests suite.
// Example RecordValidationPolicy implementation that checks record headers. Only records// containing a header with a key that matches the 'record.validation.policy' property of// the topic are accepted.publicclassRequireHeaderValidationPolicyimplementsRecordValidationPolicy {
@Overridepublicvoidconfigure(Map<String, ?> configs) { // This example doesn't use any of the broker's configuration properties. } @Overridepublicvoidclose() throwsIOException { // This example doesn't need to perform any cleanup when the broker is shutdown. } @Overridepublicvoidvalidate(TopicMetadatatopic, RecordProxyrecord) throwsInvalidRecordException { // Do any of the record headers have a key matching the 'record.validation.policy' // property of the topic being produced to? if (!record.headers().stream().filter(h->h.key().equals(topic.validationPolicy())).findFirst().isPresent()) { thrownewInvalidRecordException( String.format("Topic %s requires records to contain a header with key: %s", topic.topicIdPartition().topic(), topic.validationPolicy())); } } @OverridepublicRecordIntrospectionHintsgetHints() {// RequireHeaderValidationPolicy only requires access to the record headers.// 0 is returned for the key/value portions of the record as this policy// doesn't inspect these fields. This avoids any potential overhead in the// broker parsing the record to find fields that the policy doesn't make use of.returnnewRecordIntrospectionHints() { @Override publicbooleanaccessHeaders() { returntrue; } @Override publiclongaccessKeyBytes() { return0; } @Override publiclongaccessValueBytes() { return0; } }; }}