chia7712 commented on code in PR #19508:
URL: https://github.com/apache/kafka/pull/19508#discussion_r2080185161


##########
clients/src/main/java/org/apache/kafka/common/requests/ListGroupsRequest.java:
##########
@@ -50,8 +53,19 @@ public ListGroupsRequest build(short version) {
                         "v" + version + ", but we need v4 or newer to request 
groups by states.");
             }
             if (!data.typesFilter().isEmpty() && version < 5) {
-                throw new UnsupportedVersionException("The broker only 
supports ListGroups " +
-                    "v" + version + ", but we need v5 or newer to request 
groups by type.");
+                // Types filter is supported by brokers with version 4.0.0 or 
later. Older brokers only support
+                // classic groups, so listing consumer groups on an older 
broker does not need to use a types filter.
+                // If the types filter is only for consumer and classic, or 
just classic groups, it can be safely omitted.
+                // This allows a modern admin client to list consumer groups 
on older brokers in a straightforward way.
+                HashSet<String> typesCopy = new HashSet<>(data.typesFilter());
+                boolean containedClassic = 
typesCopy.remove(GroupType.CLASSIC.toString());
+                boolean containedConsumer = 
typesCopy.remove(GroupType.CONSUMER.toString());
+                if (!typesCopy.isEmpty() || (!containedClassic && 
containedConsumer)) {

Review Comment:
   > Modern consumer groups would be reported as classic groups, because the 
RPC response was not able to distinguish.
   
   My point was the request 
`ListGroupsOptions.withTypes(List.of(GroupType.CLASSIC))` will get both classic 
and consumer groups from 3.7 broker when KIP-848 EA enabled. That is a bit 
weird to me, as users are expected to receive only the classic groups. Hence, 
maybe we should throw `UnsupportedVersionException` for that case?



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