AndrewJSchofield commented on code in PR #17626:
URL: https://github.com/apache/kafka/pull/17626#discussion_r1824208417


##########
clients/src/main/java/org/apache/kafka/clients/admin/KafkaAdminClient.java:
##########
@@ -3490,6 +3490,138 @@ void handleFailure(Throwable throwable) {
         return new DescribeDelegationTokenResult(tokensFuture);
     }
 
+    private static final class ListGroupsResults {
+        private final List<Throwable> errors;
+        private final HashMap<String, GroupListing> listings;
+        private final HashSet<Node> remaining;
+        private final KafkaFutureImpl<Collection<Object>> future;
+
+        ListGroupsResults(Collection<Node> leaders,
+                          KafkaFutureImpl<Collection<Object>> future) {
+            this.errors = new ArrayList<>();
+            this.listings = new HashMap<>();
+            this.remaining = new HashSet<>(leaders);
+            this.future = future;
+            tryComplete();
+        }
+
+        synchronized void addError(Throwable throwable, Node node) {
+            ApiError error = ApiError.fromThrowable(throwable);
+            if (error.message() == null || error.message().isEmpty()) {
+                errors.add(error.error().exception("Error listing groups on " 
+ node));
+            } else {
+                errors.add(error.error().exception("Error listing groups on " 
+ node + ": " + error.message()));
+            }
+        }
+
+        synchronized void addListing(GroupListing listing) {
+            listings.put(listing.groupId(), listing);
+        }
+
+        synchronized void tryComplete(Node leader) {
+            remaining.remove(leader);
+            tryComplete();
+        }
+
+        private synchronized void tryComplete() {
+            if (remaining.isEmpty()) {
+                ArrayList<Object> results = new ArrayList<>(listings.values());
+                results.addAll(errors);
+                future.complete(results);
+            }
+        }
+    }
+
+    @Override
+    public ListGroupsResult listGroups(ListGroupsOptions options) {
+        final KafkaFutureImpl<Collection<Object>> all = new 
KafkaFutureImpl<>();
+        final long nowMetadata = time.milliseconds();
+        final long deadline = calcDeadlineMs(nowMetadata, options.timeoutMs());
+        runnable.call(new Call("findAllBrokers", deadline, new 
LeastLoadedNodeProvider()) {
+            @Override
+            MetadataRequest.Builder createRequest(int timeoutMs) {
+                return new MetadataRequest.Builder(new MetadataRequestData()
+                    .setTopics(Collections.emptyList())
+                    .setAllowAutoTopicCreation(true));
+            }
+
+            @Override
+            void handleResponse(AbstractResponse abstractResponse) {
+                MetadataResponse metadataResponse = (MetadataResponse) 
abstractResponse;
+                Collection<Node> nodes = metadataResponse.brokers();
+                if (nodes.isEmpty())
+                    throw new StaleMetadataException("Metadata fetch failed 
due to missing broker list");
+
+                HashSet<Node> allNodes = new HashSet<>(nodes);
+                final ListGroupsResults results = new 
ListGroupsResults(allNodes, all);
+
+                for (final Node node : allNodes) {
+                    final long nowList = time.milliseconds();
+                    runnable.call(new Call("listGroups", deadline, new 
ConstantNodeIdProvider(node.id())) {
+                        @Override
+                        ListGroupsRequest.Builder createRequest(int timeoutMs) 
{
+                            List<String> groupTypes = options.types()
+                                .stream()
+                                .map(GroupType::toString)
+                                .collect(Collectors.toList());
+                            return new ListGroupsRequest.Builder(new 
ListGroupsRequestData()
+                                .setTypesFilter(groupTypes)
+                            );
+                        }
+
+                        private void 
maybeAddGroup(ListGroupsResponseData.ListedGroup group) {
+                            final String groupId = group.groupId();
+                            final GroupType type = group.groupType().isEmpty()
+                                ? GroupType.UNKNOWN
+                                : GroupType.parse(group.groupType());
+                            final String protocolType = group.protocolType();
+                            final GroupListing groupListing = new GroupListing(
+                                groupId,
+                                Optional.of(type),

Review Comment:
   This new code is part of AK 4.0. If you use this new admin client to list 
groups for a broker which does not support ListGroups v5 or later, it cannot 
return the group type. In this case, I think the `GroupListing` should use 
`Optional.empty()` for the group type.
   
   I don't have a problem with `ListGroupsOptions.withTypes` not being able to 
request information on groups whose type cannot be returned. Using a set of 
`Optional` is cumbersome for a situation which is unlikely to be used in 
practice.
   
   If you use this admin client to list groups for a future broker that has 
more group types than this admin client understands, I think the `GroupListing` 
should use `Optional.of(GroupType.UNKNOWN)` for the group type.
   
   I think it's very unlikely that a user would want to query groups whose type 
cannot be understood. Technically, `GroupType.UNKNOWN` exists so it could be 
supplied in the `withTypes` method. It's not a sensible thing to attempt to do. 
I wonder whether the best thing would be to ensure that `GroupType.UNKNOWN` is 
not specified in the set of group types.



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