C0urante commented on a change in pull request #11775:
URL: https://github.com/apache/kafka/pull/11775#discussion_r819937017
##########
File path:
connect/api/src/main/java/org/apache/kafka/connect/source/SourceConnector.java
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@@ -28,4 +30,46 @@
protected SourceConnectorContext context() {
return (SourceConnectorContext) context;
}
+
+ /**
+ * Signals whether the connector supports exactly-once delivery guarantees
with a proposed configuration.
+ * Developers can assume that worker-level exactly-once support is enabled
when this method is invoked.
+ *
+ * <p>For backwards compatibility, the default implementation will return
{@code null}, but connector developers are
+ * strongly encouraged to override this method to return a non-null value
such as
+ * {@link ExactlyOnceSupport#SUPPORTED SUPPORTED} or {@link
ExactlyOnceSupport#UNSUPPORTED UNSUPPORTED}.
+ *
+ * <p>Similar to {@link #validate(Map) validate}, this method may be
called by the runtime before the
+ * {@link #start(Map) start} method is invoked when the connector will be
run with exactly-once support.
+ *
+ * @param connectorConfig the configuration that will be used for the
connector.
+ * @return {@link ExactlyOnceSupport#SUPPORTED} if the connector can
provide exactly-once support with the given
+ * configuration, and {@link ExactlyOnceSupport#UNSUPPORTED} if it cannot.
If this method is overridden by a
+ * connector, should not be {@code null}, but if {@code null}, it will be
assumed that the connector cannot provide
+ * exactly-once guarantees.
Review comment:
We do technically allow `null`, but we discourage it. This allows us to
differentiate between a connector that has implemented this method and
explicitly does not provide exactly-once support (signaled by returning
`ExactlyOnceSupport.UNSUPPORTED`), and a connector that hasn't implemented this
method at all (signaled by returning `null`). This comes into play in the
downstream [preflight validation
PR](https://github.com/apache/kafka/pull/11776):
https://github.com/C0urante/kafka/blob/b4976e82aec1c864bd25d660b4042a71e03b7c47/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/distributed/DistributedHerder.java#L892-L899
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