Dry up collection writing to StreamOutput (#86386)

Small weekend project around automated refactoring:
We have endless duplication here, drying up some of it.

modules/legacy-geo/src/main/java/org/elasticsearch/legacygeo/builders/GeometryCollectionBuilder.java

@@ -51,10 +51,7 @@ public class GeometryCollectionBuilder extends ShapeBuilder<Shape, GeometryColle
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(shapes.size());
+        out.writeNamedWriteableList(shapes);
-        for (ShapeBuilder<?, ?, ?> shape : shapes) {
-            out.writeNamedWriteable(shape);
-        }
     }
 
     public GeometryCollectionBuilder shape(ShapeBuilder<?, ?, ?> shape) {

modules/legacy-geo/src/main/java/org/elasticsearch/legacygeo/builders/MultiLineStringBuilder.java

@@ -49,10 +49,7 @@ public class MultiLineStringBuilder extends ShapeBuilder<JtsGeometry, org.elasti
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(lines.size());
+        out.writeList(lines);
-        for (LineStringBuilder line : lines) {
-            line.writeTo(out);
-        }
     }
 
     public MultiLineStringBuilder linestring(LineStringBuilder line) {

modules/legacy-geo/src/main/java/org/elasticsearch/legacygeo/builders/MultiPolygonBuilder.java

@@ -63,10 +63,7 @@ public class MultiPolygonBuilder extends ShapeBuilder<Shape, MultiPolygon, Multi
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         orientation.writeTo(out);
-        out.writeVInt(polygons.size());
+        out.writeList(polygons);
-        for (PolygonBuilder polygon : polygons) {
-            polygon.writeTo(out);
-        }
     }
 
     public Orientation orientation() {

modules/legacy-geo/src/main/java/org/elasticsearch/legacygeo/builders/PolygonBuilder.java

@@ -93,10 +93,7 @@ public class PolygonBuilder extends ShapeBuilder<JtsGeometry, org.elasticsearch.
     public void writeTo(StreamOutput out) throws IOException {
         shell.writeTo(out);
         orientation.writeTo(out);
-        out.writeVInt(holes.size());
+        out.writeList(holes);
-        for (LineStringBuilder hole : holes) {
-            hole.writeTo(out);
-        }
     }
 
     public Orientation orientation() {

modules/legacy-geo/src/main/java/org/elasticsearch/legacygeo/builders/ShapeBuilder.java

@@ -107,10 +107,7 @@ public abstract class ShapeBuilder<T extends Shape, G extends org.elasticsearch.
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(coordinates.size());
+        out.writeCollection(coordinates, (o, p) -> writeCoordinateTo(p, o));
-        for (Coordinate point : coordinates) {
-            writeCoordinateTo(point, out);
-        }
     }
 
     protected static void writeCoordinateTo(Coordinate coordinate, StreamOutput out) throws IOException {

modules/percolator/src/main/java/org/elasticsearch/percolator/PercolateQueryBuilder.java

@@ -275,10 +275,7 @@ public class PercolateQueryBuilder extends AbstractQueryBuilder<PercolateQueryBu
         } else {
             out.writeBoolean(false);
         }
-        out.writeVInt(documents.size());
+        out.writeCollection(documents, StreamOutput::writeBytesReference);
-        for (BytesReference document : documents) {
-            out.writeBytesReference(document);
-        }
         if (documents.isEmpty() == false) {
             XContentHelper.writeTo(out, documentXContentType);
         }

modules/rank-eval/src/main/java/org/elasticsearch/index/rankeval/RankEvalResponse.java

@@ -88,16 +88,8 @@ public class RankEvalResponse extends ActionResponse implements ToXContentObject
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeDouble(metricScore);
-        out.writeVInt(details.size());
+        out.writeMap(details, StreamOutput::writeString, (o, v) -> v.writeTo(o));
-        for (String queryId : details.keySet()) {
+        out.writeMap(failures, StreamOutput::writeString, StreamOutput::writeException);
-            out.writeString(queryId);
-            details.get(queryId).writeTo(out);
-        }
-        out.writeVInt(failures.size());
-        for (String queryId : failures.keySet()) {
-            out.writeString(queryId);
-            out.writeException(failures.get(queryId));
-        }
     }
 
     @Override

modules/rank-eval/src/main/java/org/elasticsearch/index/rankeval/RankEvalSpec.java

@@ -96,16 +96,9 @@ public class RankEvalSpec implements Writeable, ToXContentObject {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(ratedRequests.size());
+        out.writeList(ratedRequests);
-        for (RatedRequest spec : ratedRequests) {
-            spec.writeTo(out);
-        }
         out.writeNamedWriteable(metric);
-        out.writeVInt(templates.size());
+        out.writeMap(templates, StreamOutput::writeString, (o, v) -> v.writeTo(o));
-        for (Entry<String, Script> entry : templates.entrySet()) {
-            out.writeString(entry.getKey());
-            entry.getValue().writeTo(out);
-        }
         out.writeVInt(maxConcurrentSearches);
     }
 

server/src/main/java/org/elasticsearch/action/admin/indices/analyze/AnalyzeAction.java

@@ -646,18 +646,12 @@ public class AnalyzeAction extends ActionType<AnalyzeAction.Response> {
             if (customAnalyzer) {
                 tokenizer.writeTo(out);
                 if (charfilters != null) {
-                    out.writeVInt(charfilters.length);
+                    out.writeArray(charfilters);
-                    for (CharFilteredText charfilter : charfilters) {
-                        charfilter.writeTo(out);
-                    }
                 } else {
                     out.writeVInt(0);
                 }
                 if (tokenfilters != null) {
-                    out.writeVInt(tokenfilters.length);
+                    out.writeArray(tokenfilters);
-                    for (AnalyzeTokenList tokenfilter : tokenfilters) {
-                        tokenfilter.writeTo(out);
-                    }
                 } else {
                     out.writeVInt(0);
                 }

server/src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexRequest.java

@@ -465,10 +465,7 @@ public class CreateIndexRequest extends AcknowledgedRequest<CreateIndexRequest>
         } else {
             out.writeString(mappings);
         }
-        out.writeVInt(aliases.size());
+        out.writeCollection(aliases);
-        for (Alias alias : aliases) {
-            alias.writeTo(out);
-        }
         waitForActiveShards.writeTo(out);
         if (out.getVersion().onOrAfter(Version.V_7_12_0)) {
             out.writeString(origin);

server/src/main/java/org/elasticsearch/action/admin/indices/rollover/RolloverResponse.java

@@ -120,11 +120,7 @@ public final class RolloverResponse extends ShardsAcknowledgedResponse implement
         super.writeTo(out);
         out.writeString(oldIndex);
         out.writeString(newIndex);
-        out.writeVInt(conditionStatus.size());
+        out.writeMap(conditionStatus, StreamOutput::writeString, StreamOutput::writeBoolean);
-        for (Map.Entry<String, Boolean> entry : conditionStatus.entrySet()) {
-            out.writeString(entry.getKey());
-            out.writeBoolean(entry.getValue());
-        }
         out.writeBoolean(dryRun);
         out.writeBoolean(rolledOver);
         out.writeBoolean(shardsAcknowledged);

server/src/main/java/org/elasticsearch/action/admin/indices/shards/IndicesShardStoresRequest.java

@@ -52,10 +52,7 @@ public class IndicesShardStoresRequest extends MasterNodeReadRequest<IndicesShar
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         out.writeStringArrayNullable(indices);
-        out.writeVInt(statuses.size());
+        out.writeCollection(statuses, (o, v) -> o.writeByte(v.value()));
-        for (ClusterHealthStatus status : statuses) {
-            out.writeByte(status.value());
-        }
         indicesOptions.writeIndicesOptions(out);
     }
 

server/src/main/java/org/elasticsearch/action/admin/indices/shards/IndicesShardStoresResponse.java

@@ -269,13 +269,11 @@ public class IndicesShardStoresResponse extends ActionResponse implements ToXCon
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeMap(storeStatuses, StreamOutput::writeString, (o, v) -> {
+        out.writeMap(
-            o.writeVInt(v.size());
+            storeStatuses,
-            for (Map.Entry<Integer, List<StoreStatus>> shardStatusesEntry : v.entrySet()) {
+            StreamOutput::writeString,
-                o.writeInt(shardStatusesEntry.getKey());
+            (o, v) -> o.writeMap(v, StreamOutput::writeInt, StreamOutput::writeCollection)
-                o.writeCollection(shardStatusesEntry.getValue());
+        );
-            }
-        });
         out.writeList(failures);
     }
 

server/src/main/java/org/elasticsearch/action/admin/indices/template/get/GetIndexTemplatesResponse.java

@@ -42,10 +42,7 @@ public class GetIndexTemplatesResponse extends ActionResponse implements ToXCont
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(indexTemplates.size());
+        out.writeCollection(indexTemplates);
-        for (IndexTemplateMetadata indexTemplate : indexTemplates) {
-            indexTemplate.writeTo(out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/admin/indices/template/put/PutIndexTemplateRequest.java

@@ -456,10 +456,7 @@ public class PutIndexTemplateRequest extends MasterNodeRequest<PutIndexTemplateR
         } else {
             out.writeOptionalString(mappings);
         }
-        out.writeVInt(aliases.size());
+        out.writeCollection(aliases);
-        for (Alias alias : aliases) {
-            alias.writeTo(out);
-        }
         out.writeOptionalVInt(version);
     }
 }

server/src/main/java/org/elasticsearch/action/ingest/GetPipelineResponse.java

@@ -64,10 +64,7 @@ public class GetPipelineResponse extends ActionResponse implements StatusToXCont
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(pipelines.size());
+        out.writeCollection(pipelines);
-        for (PipelineConfiguration pipeline : pipelines) {
-            pipeline.writeTo(out);
-        }
         out.writeBoolean(summary);
     }
 

server/src/main/java/org/elasticsearch/action/ingest/SimulateDocumentVerboseResult.java

@@ -55,10 +55,7 @@ public final class SimulateDocumentVerboseResult implements SimulateDocumentResu
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(processorResults.size());
+        out.writeCollection(processorResults);
-        for (SimulateProcessorResult result : processorResults) {
-            result.writeTo(out);
-        }
     }
 
     public List<SimulateProcessorResult> getProcessorResults() {

server/src/main/java/org/elasticsearch/action/ingest/SimulatePipelineResponse.java

@@ -121,10 +121,7 @@ public class SimulatePipelineResponse extends ActionResponse implements ToXConte
     public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalString(pipelineId);
         out.writeBoolean(verbose);
-        out.writeVInt(results.size());
+        out.writeCollection(results);
-        for (SimulateDocumentResult response : results) {
-            response.writeTo(out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/search/MultiSearchRequest.java

@@ -147,10 +147,7 @@ public class MultiSearchRequest extends ActionRequest implements CompositeIndice
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         out.writeVInt(maxConcurrentSearchRequests);
-        out.writeVInt(requests.size());
+        out.writeCollection(requests);
-        for (SearchRequest request : requests) {
-            request.writeTo(out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/search/TransportSearchHelper.java

@@ -39,19 +39,18 @@ public final class TransportSearchHelper {
             BytesStreamOutput out = new BytesStreamOutput();
             out.writeString(INCLUDE_CONTEXT_UUID);
             out.writeString(searchPhaseResults.length() == 1 ? ParsedScrollId.QUERY_AND_FETCH_TYPE : ParsedScrollId.QUERY_THEN_FETCH_TYPE);
-            out.writeVInt(searchPhaseResults.asList().size());
+            out.writeCollection(searchPhaseResults.asList(), (o, searchPhaseResult) -> {
-            for (SearchPhaseResult searchPhaseResult : searchPhaseResults.asList()) {
+                o.writeString(searchPhaseResult.getContextId().getSessionId());
-                out.writeString(searchPhaseResult.getContextId().getSessionId());
+                o.writeLong(searchPhaseResult.getContextId().getId());
-                out.writeLong(searchPhaseResult.getContextId().getId());
                 SearchShardTarget searchShardTarget = searchPhaseResult.getSearchShardTarget();
                 if (searchShardTarget.getClusterAlias() != null) {
-                    out.writeString(
+                    o.writeString(
                         RemoteClusterAware.buildRemoteIndexName(searchShardTarget.getClusterAlias(), searchShardTarget.getNodeId())
                     );
                 } else {
-                    out.writeString(searchShardTarget.getNodeId());
+                    o.writeString(searchShardTarget.getNodeId());
                 }
-            }
+            });
             return Base64.getUrlEncoder().encodeToString(out.copyBytes().array());
         } catch (IOException e) {
             throw new UncheckedIOException(e);

server/src/main/java/org/elasticsearch/action/support/broadcast/BroadcastResponse.java

@@ -137,10 +137,7 @@ public class BroadcastResponse extends ActionResponse implements ToXContentObjec
         out.writeVInt(totalShards);
         out.writeVInt(successfulShards);
         out.writeVInt(failedShards);
-        out.writeVInt(shardFailures.length);
+        out.writeArray(shardFailures);
-        for (DefaultShardOperationFailedException exp : shardFailures) {
-            exp.writeTo(out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/support/broadcast/node/TransportBroadcastByNodeAction.java

@@ -671,10 +671,7 @@ public abstract class TransportBroadcastByNodeAction<
         public void writeTo(StreamOutput out) throws IOException {
             out.writeString(nodeId);
             out.writeVInt(totalShards);
-            out.writeVInt(results.size());
+            out.writeCollection(results, StreamOutput::writeOptionalWriteable);
-            for (ShardOperationResult result : results) {
-                out.writeOptionalWriteable(result);
-            }
             out.writeBoolean(exceptions != null);
             if (exceptions != null) {
                 out.writeList(exceptions);

server/src/main/java/org/elasticsearch/action/support/replication/ReplicationResponse.java

@@ -135,10 +135,7 @@ public class ReplicationResponse extends ActionResponse {
         public void writeTo(StreamOutput out) throws IOException {
             out.writeVInt(total);
             out.writeVInt(successful);
-            out.writeVInt(failures.length);
+            out.writeArray(failures);
-            for (Failure failure : failures) {
-                failure.writeTo(out);
-            }
         }
 
         @Override

server/src/main/java/org/elasticsearch/action/support/tasks/BaseTasksResponse.java

@@ -61,14 +61,8 @@ public class BaseTasksResponse extends ActionResponse {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(taskFailures.size());
+        out.writeCollection(taskFailures);
-        for (TaskOperationFailure exp : taskFailures) {
+        out.writeCollection(nodeFailures);
-            exp.writeTo(out);
-        }
-        out.writeVInt(nodeFailures.size());
-        for (ElasticsearchException exp : nodeFailures) {
-            exp.writeTo(out);
-        }
     }
 
     /**

server/src/main/java/org/elasticsearch/action/support/tasks/TransportTasksAction.java

@@ -393,22 +393,10 @@ public abstract class TransportTasksAction<
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeString(nodeId);
-            out.writeVInt(results.size());
+            out.writeCollection(results, StreamOutput::writeOptionalWriteable);
-            for (TaskResponse result : results) {
-                if (result != null) {
-                    out.writeBoolean(true);
-                    result.writeTo(out);
-                } else {
-                    out.writeBoolean(false);
-                }
-            }
             out.writeBoolean(exceptions != null);
             if (exceptions != null) {
-                int taskFailures = exceptions.size();
+                out.writeCollection(exceptions);
-                out.writeVInt(taskFailures);
-                for (TaskOperationFailure exception : exceptions) {
-                    exception.writeTo(out);
-                }
             }
         }
     }

server/src/main/java/org/elasticsearch/cluster/ClusterInfo.java

@@ -116,15 +116,11 @@ public class ClusterInfo implements ToXContentFragment, Writeable {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(this.leastAvailableSpaceUsage.size());
+        out.writeMap(this.leastAvailableSpaceUsage, StreamOutput::writeString, (o, v) -> v.writeTo(o));
-        for (Map.Entry<String, DiskUsage> c : this.leastAvailableSpaceUsage.entrySet()) {
-            out.writeString(c.getKey());
-            c.getValue().writeTo(out);
-        }
         out.writeMap(this.mostAvailableSpaceUsage, StreamOutput::writeString, (o, v) -> v.writeTo(o));
-        out.writeMap(this.shardSizes, StreamOutput::writeString, (o, v) -> out.writeLong(v == null ? -1 : v));
+        out.writeMap(this.shardSizes, StreamOutput::writeString, (o, v) -> o.writeLong(v == null ? -1 : v));
         if (out.getVersion().onOrAfter(DATA_SET_SIZE_SIZE_VERSION)) {
-            out.writeMap(this.shardDataSetSizes, (o, s) -> s.writeTo(o), (o, v) -> out.writeLong(v));
+            out.writeMap(this.shardDataSetSizes, (o, s) -> s.writeTo(o), StreamOutput::writeLong);
         }
         out.writeMap(this.routingToDataPath, (o, k) -> k.writeTo(o), StreamOutput::writeString);
         if (out.getVersion().onOrAfter(StoreStats.RESERVED_BYTES_VERSION)) {
@@ -316,10 +312,7 @@ public class ClusterInfo implements ToXContentFragment, Writeable {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeVLong(total);
-            out.writeVInt(shardIds.size());
+            out.writeCollection(shardIds);
-            for (ShardId shardIdCursor : shardIds) {
-                shardIdCursor.writeTo(out);
-            }
         }
 
         public long getTotal() {

server/src/main/java/org/elasticsearch/cluster/RestoreInProgress.java

@@ -370,14 +370,13 @@ public class RestoreInProgress extends AbstractNamedDiffable<Custom> implements
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(entries.size());
+        out.writeCollection(entries.values(), (o, entry) -> {
-        for (Entry entry : entries.values()) {
+            o.writeString(entry.uuid);
-            out.writeString(entry.uuid);
+            entry.snapshot().writeTo(o);
-            entry.snapshot().writeTo(out);
+            o.writeByte(entry.state().value());
-            out.writeByte(entry.state().value());
+            o.writeStringCollection(entry.indices);
-            out.writeStringCollection(entry.indices);
+            o.writeMap(entry.shards);
-            out.writeMap(entry.shards);
+        });
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetadata.java

@@ -1247,24 +1247,14 @@ public class IndexMetadata implements Diffable<IndexMetadata>, ToXContentFragmen
                 mapping.writeTo(out);
             }
         }
-        out.writeVInt(aliases.size());
+        out.writeCollection(aliases.values());
-        for (AliasMetadata aliasMetadata : aliases.values()) {
+        out.writeMap(customData, StreamOutput::writeString, (o, v) -> v.writeTo(o));
-            aliasMetadata.writeTo(out);
+        out.writeMap(
-        }
+            inSyncAllocationIds,
-        out.writeVInt(customData.size());
+            StreamOutput::writeVInt,
-        for (final Map.Entry<String, DiffableStringMap> cursor : customData.entrySet()) {
+            (o, v) -> DiffableUtils.StringSetValueSerializer.getInstance().write(v, o)
-            out.writeString(cursor.getKey());
+        );
-            cursor.getValue().writeTo(out);
+        out.writeCollection(rolloverInfos.values());
-        }
-        out.writeVInt(inSyncAllocationIds.size());
-        for (Map.Entry<Integer, Set<String>> cursor : inSyncAllocationIds.entrySet()) {
-            out.writeVInt(cursor.getKey());
-            DiffableUtils.StringSetValueSerializer.getInstance().write(cursor.getValue(), out);
-        }
-        out.writeVInt(rolloverInfos.size());
-        for (RolloverInfo rolloverInfo : rolloverInfos.values()) {
-            rolloverInfo.writeTo(out);
-        }
         if (out.getVersion().onOrAfter(SYSTEM_INDEX_FLAG_ADDED)) {
             out.writeBoolean(isSystem);
         }

server/src/main/java/org/elasticsearch/cluster/metadata/IndexTemplateMetadata.java

@@ -207,15 +207,8 @@ public class IndexTemplateMetadata implements SimpleDiffable<IndexTemplateMetada
         out.writeInt(order);
         out.writeStringCollection(patterns);
         Settings.writeSettingsToStream(settings, out);
-        out.writeVInt(mappings.size());
+        out.writeMap(mappings, StreamOutput::writeString, (o, v) -> v.writeTo(o));
-        for (Map.Entry<String, CompressedXContent> cursor : mappings.entrySet()) {
+        out.writeCollection(aliases.values());
-            out.writeString(cursor.getKey());
-            cursor.getValue().writeTo(out);
-        }
-        out.writeVInt(aliases.size());
-        for (AliasMetadata aliasMetadata : aliases.values()) {
-            aliasMetadata.writeTo(out);
-        }
         out.writeOptionalVInt(version);
     }
 

server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java

@@ -1212,10 +1212,7 @@ public class Metadata extends AbstractCollection<IndexMetadata> implements Diffa
         for (IndexMetadata indexMetadata : this) {
             indexMetadata.writeTo(out, writeMappingsHash);
         }
-        out.writeVInt(templates.size());
+        out.writeCollection(templates.values());
-        for (IndexTemplateMetadata template : templates.values()) {
-            template.writeTo(out);
-        }
         VersionedNamedWriteable.writeVersionedWritables(out, customs);
     }
 

server/src/main/java/org/elasticsearch/cluster/node/DiscoveryNode.java

@@ -388,12 +388,11 @@ public class DiscoveryNode implements Writeable, ToXContentFragment {
         out.writeString(hostAddress);
         address.writeTo(out);
         out.writeMap(attributes, StreamOutput::writeString, StreamOutput::writeString);
-        out.writeVInt(roles.size());
+        out.writeCollection(roles, (o, role) -> {
-        for (final DiscoveryNodeRole role : roles) {
+            o.writeString(role.roleName());
-            out.writeString(role.roleName());
+            o.writeString(role.roleNameAbbreviation());
-            out.writeString(role.roleNameAbbreviation());
+            o.writeBoolean(role.canContainData());
-            out.writeBoolean(role.canContainData());
+        });
-        }
         Version.writeVersion(version, out);
         if (out.getVersion().onOrAfter(EXTERNAL_ID_VERSION)) {
             out.writeString(externalId);

server/src/main/java/org/elasticsearch/cluster/node/DiscoveryNodes.java

@@ -574,10 +574,7 @@ public class DiscoveryNodes extends AbstractCollection<DiscoveryNode> implements
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalString(masterNodeId);
-        out.writeVInt(nodes.size());
+        out.writeCollection(nodes.values());
-        for (DiscoveryNode node : this) {
-            node.writeTo(out);
-        }
     }
 
     public static DiscoveryNodes readFrom(StreamInput in, DiscoveryNode localNode) throws IOException {

server/src/main/java/org/elasticsearch/cluster/routing/IndexRoutingTable.java

@@ -313,10 +313,7 @@ public class IndexRoutingTable implements SimpleDiffable<IndexRoutingTable> {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         index.writeTo(out);
-        out.writeVInt(shards.length);
+        out.writeArray((o, s) -> IndexShardRoutingTable.Builder.writeToThin(s, o), shards);
-        for (IndexShardRoutingTable indexShard : this.shards) {
-            IndexShardRoutingTable.Builder.writeToThin(indexShard, out);
-        }
     }
 
     public static Builder builder(Index index) {

server/src/main/java/org/elasticsearch/cluster/routing/IndexShardRoutingTable.java

@@ -620,11 +620,7 @@ public class IndexShardRoutingTable {
 
         public static void writeToThin(IndexShardRoutingTable indexShard, StreamOutput out) throws IOException {
             out.writeVInt(indexShard.shardId.id());
-
+            out.writeArray((o, v) -> v.writeToThin(o), indexShard.shards);
-            out.writeVInt(indexShard.shards.length);
-            for (ShardRouting entry : indexShard.shards) {
-                entry.writeToThin(out);
-            }
         }
 
     }

server/src/main/java/org/elasticsearch/cluster/routing/RoutingTable.java

@@ -343,10 +343,7 @@ public class RoutingTable implements Iterable<IndexRoutingTable>, Diffable<Routi
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeLong(version);
-        out.writeVInt(indicesRouting.size());
+        out.writeCollection(indicesRouting.values());
-        for (IndexRoutingTable index : indicesRouting.values()) {
-            index.writeTo(out);
-        }
     }
 
     private static class RoutingTableDiff implements Diff<RoutingTable> {

server/src/main/java/org/elasticsearch/cluster/routing/allocation/RoutingExplanations.java

@@ -68,10 +68,7 @@ public class RoutingExplanations implements ToXContentFragment {
      * Write the RoutingExplanations object
      */
     public static void writeTo(RoutingExplanations explanations, StreamOutput out) throws IOException {
-        out.writeVInt(explanations.explanations.size());
+        out.writeCollection(explanations.explanations, (o, v) -> RerouteExplanation.writeTo(v, o));
-        for (RerouteExplanation explanation : explanations.explanations) {
-            RerouteExplanation.writeTo(explanation, out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/cluster/routing/allocation/command/AllocationCommands.java

@@ -99,10 +99,7 @@ public class AllocationCommands implements ToXContentFragment {
      * @throws IOException if something happens during write
      */
     public static void writeTo(AllocationCommands commands, StreamOutput out) throws IOException {
-        out.writeVInt(commands.commands.size());
+        out.writeNamedWriteableList(commands.commands);
-        for (AllocationCommand command : commands.commands) {
-            out.writeNamedWriteable(command);
-        }
     }
 
     /**

server/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/Decision.java

@@ -339,10 +339,7 @@ public abstract class Decision implements ToXContent, Writeable {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeBoolean(true); // flag indicating it is a multi decision
-            out.writeVInt(getDecisions().size());
+            out.writeCollection(getDecisions());
-            for (Decision d : getDecisions()) {
-                d.writeTo(out);
-            }
         }
     }
 }

server/src/main/java/org/elasticsearch/common/lucene/Lucene.java

@@ -414,20 +414,12 @@ public class Lucene {
             out.writeFloat(topDocs.maxScore);
 
             out.writeArray(Lucene::writeSortField, topFieldDocs.fields);
-
+            out.writeArray((o, doc) -> writeFieldDoc(o, (FieldDoc) doc), topFieldDocs.scoreDocs);
-            out.writeVInt(topDocs.topDocs.scoreDocs.length);
-            for (ScoreDoc doc : topFieldDocs.scoreDocs) {
-                writeFieldDoc(out, (FieldDoc) doc);
-            }
         } else {
             out.writeByte((byte) 0);
             writeTotalHits(out, topDocs.topDocs.totalHits);
             out.writeFloat(topDocs.maxScore);
-
+            out.writeArray(Lucene::writeScoreDoc, topDocs.topDocs.scoreDocs);
-            out.writeVInt(topDocs.topDocs.scoreDocs.length);
-            for (ScoreDoc doc : topDocs.topDocs.scoreDocs) {
-                writeScoreDoc(out, doc);
-            }
         }
     }
 
@@ -495,10 +487,7 @@ public class Lucene {
     }
 
     public static void writeFieldDoc(StreamOutput out, FieldDoc fieldDoc) throws IOException {
-        out.writeVInt(fieldDoc.fields.length);
+        out.writeArray(Lucene::writeSortValue, fieldDoc.fields);
-        for (Object field : fieldDoc.fields) {
-            writeSortValue(out, field);
-        }
         out.writeVInt(fieldDoc.doc);
         out.writeFloat(fieldDoc.score);
     }
@@ -627,10 +616,7 @@ public class Lucene {
         out.writeBoolean(explanation.isMatch());
         out.writeString(explanation.getDescription());
         Explanation[] subExplanations = explanation.getDetails();
-        out.writeVInt(subExplanations.length);
+        out.writeArray(Lucene::writeExplanation, subExplanations);
-        for (Explanation subExp : subExplanations) {
-            writeExplanation(out, subExp);
-        }
         if (explanation.isMatch()) {
             writeExplanationValue(out, explanation.getValue());
         }

server/src/main/java/org/elasticsearch/common/util/concurrent/ThreadContext.java

@@ -685,12 +685,7 @@ public final class ThreadContext implements Writeable {
                 requestHeaders.putAll(this.requestHeaders);
             }
 
-            out.writeVInt(requestHeaders.size());
+            out.writeMap(requestHeaders, StreamOutput::writeString, StreamOutput::writeString);
-            for (Map.Entry<String, String> entry : requestHeaders.entrySet()) {
-                out.writeString(entry.getKey());
-                out.writeString(entry.getValue());
-            }
-
             out.writeMap(responseHeaders, StreamOutput::writeString, StreamOutput::writeStringCollection);
         }
     }

server/src/main/java/org/elasticsearch/index/engine/CommitStats.java

@@ -78,11 +78,7 @@ public final class CommitStats implements Writeable, ToXContentFragment {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(userData.size());
+        out.writeMap(userData, StreamOutput::writeString, StreamOutput::writeString);
-        for (Map.Entry<String, String> entry : userData.entrySet()) {
-            out.writeString(entry.getKey());
-            out.writeString(entry.getValue());
-        }
         out.writeLong(generation);
         out.writeOptionalString(id);
         out.writeInt(numDocs);

server/src/main/java/org/elasticsearch/index/engine/Segment.java

@@ -219,29 +219,28 @@ public class Segment implements Writeable {
             out.writeVInt(0);
             return;
         }
-        out.writeVInt(sort.getSort().length);
+        out.writeArray((o, field) -> {
-        for (SortField field : sort.getSort()) {
+            o.writeString(field.getField());
-            out.writeString(field.getField());
             if (field instanceof SortedSetSortField) {
-                out.writeByte((byte) 0);
+                o.writeByte((byte) 0);
-                out.writeOptionalBoolean(field.getMissingValue() == null ? null : field.getMissingValue() == SortField.STRING_FIRST);
+                o.writeOptionalBoolean(field.getMissingValue() == null ? null : field.getMissingValue() == SortField.STRING_FIRST);
-                out.writeBoolean(((SortedSetSortField) field).getSelector() == SortedSetSelector.Type.MAX);
+                o.writeBoolean(((SortedSetSortField) field).getSelector() == SortedSetSelector.Type.MAX);
-                out.writeBoolean(field.getReverse());
+                o.writeBoolean(field.getReverse());
             } else if (field instanceof SortedNumericSortField) {
                 switch (((SortedNumericSortField) field).getNumericType()) {
-                    case INT -> out.writeByte((byte) 1);
+                    case INT -> o.writeByte((byte) 1);
-                    case FLOAT -> out.writeByte((byte) 2);
+                    case FLOAT -> o.writeByte((byte) 2);
-                    case DOUBLE -> out.writeByte((byte) 3);
+                    case DOUBLE -> o.writeByte((byte) 3);
-                    case LONG -> out.writeByte((byte) 4);
+                    case LONG -> o.writeByte((byte) 4);
                     default -> throw new IOException("invalid index sort field:" + field);
                 }
-                out.writeGenericValue(field.getMissingValue());
+                o.writeGenericValue(field.getMissingValue());
-                out.writeBoolean(((SortedNumericSortField) field).getSelector() == SortedNumericSelector.Type.MAX);
+                o.writeBoolean(((SortedNumericSortField) field).getSelector() == SortedNumericSelector.Type.MAX);
-                out.writeBoolean(field.getReverse());
+                o.writeBoolean(field.getReverse());
             } else {
                 throw new IOException("invalid index sort field:" + field);
             }
-        }
+        }, sort.getSort());
     }
 
     private static void readRamTree(StreamInput in) throws IOException {

server/src/main/java/org/elasticsearch/index/engine/SegmentsStats.java

@@ -224,10 +224,7 @@ public class SegmentsStats implements Writeable, ToXContentFragment {
         out.writeLong(bitsetMemoryInBytes);
         out.writeLong(maxUnsafeAutoIdTimestamp);
 
-        out.writeVInt(files.size());
+        out.writeCollection(files.values());
-        for (FileStats file : files.values()) {
-            file.writeTo(out);
-        }
     }
 
     public void clearFiles() {

server/src/main/java/org/elasticsearch/index/query/GeoPolygonQueryBuilder.java

@@ -105,10 +105,7 @@ public class GeoPolygonQueryBuilder extends AbstractQueryBuilder<GeoPolygonQuery
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeString(fieldName);
-        out.writeVInt(shell.size());
+        out.writeCollection(shell, StreamOutput::writeGeoPoint);
-        for (GeoPoint point : shell) {
-            out.writeGeoPoint(point);
-        }
         validationMethod.writeTo(out);
         out.writeBoolean(ignoreUnmapped);
     }

server/src/main/java/org/elasticsearch/index/query/InnerHitBuilder.java

@@ -223,10 +223,7 @@ public final class InnerHitBuilder implements Writeable, ToXContentObject {
         boolean hasSorts = sorts != null;
         out.writeBoolean(hasSorts);
         if (hasSorts) {
-            out.writeVInt(sorts.size());
+            out.writeNamedWriteableList(sorts);
-            for (SortBuilder<?> sort : sorts) {
-                out.writeNamedWriteable(sort);
-            }
         }
         out.writeOptionalWriteable(highlightBuilder);
         out.writeOptionalWriteable(innerCollapseBuilder);

server/src/main/java/org/elasticsearch/index/query/MultiMatchQueryBuilder.java

@@ -234,11 +234,7 @@ public class MultiMatchQueryBuilder extends AbstractQueryBuilder<MultiMatchQuery
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeGenericValue(value);
-        out.writeVInt(fieldsBoosts.size());
+        out.writeMap(fieldsBoosts, StreamOutput::writeString, StreamOutput::writeFloat);
-        for (Map.Entry<String, Float> fieldsEntry : fieldsBoosts.entrySet()) {
-            out.writeString(fieldsEntry.getKey());
-            out.writeFloat(fieldsEntry.getValue());
-        }
         type.writeTo(out);
         operator.writeTo(out);
         out.writeOptionalString(analyzer);

server/src/main/java/org/elasticsearch/index/query/QueryStringQueryBuilder.java

@@ -192,11 +192,7 @@ public class QueryStringQueryBuilder extends AbstractQueryBuilder<QueryStringQue
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeString(this.queryString);
         out.writeOptionalString(this.defaultField);
-        out.writeVInt(this.fieldsAndWeights.size());
+        out.writeMap(this.fieldsAndWeights, StreamOutput::writeString, StreamOutput::writeFloat);
-        for (Map.Entry<String, Float> fieldsEntry : this.fieldsAndWeights.entrySet()) {
-            out.writeString(fieldsEntry.getKey());
-            out.writeFloat(fieldsEntry.getValue());
-        }
         this.defaultOperator.writeTo(out);
         out.writeOptionalString(this.analyzer);
         out.writeOptionalString(this.quoteAnalyzer);

server/src/main/java/org/elasticsearch/index/reindex/BulkByScrollTask.java

@@ -556,10 +556,7 @@ public class BulkByScrollTask extends CancellableTask {
             out.writeFloat(requestsPerSecond);
             out.writeOptionalString(reasonCancelled);
             out.writeTimeValue(throttledUntil);
-            out.writeVInt(sliceStatuses.size());
+            out.writeCollection(sliceStatuses, StreamOutput::writeOptionalWriteable);
-            for (StatusOrException sliceStatus : sliceStatuses) {
-                out.writeOptionalWriteable(sliceStatus);
-            }
         }
 
         @Override

server/src/main/java/org/elasticsearch/indices/NodeIndicesStats.java

@@ -169,14 +169,7 @@ public class NodeIndicesStats implements Writeable, ToXContentFragment {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         stats.writeTo(out);
-        out.writeVInt(statsByShard.size());
+        out.writeMap(statsByShard, (o, k) -> k.writeTo(o), StreamOutput::writeList);
-        for (Map.Entry<Index, List<IndexShardStats>> entry : statsByShard.entrySet()) {
-            entry.getKey().writeTo(out);
-            out.writeVInt(entry.getValue().size());
-            for (IndexShardStats indexShardStats : entry.getValue()) {
-                indexShardStats.writeTo(out);
-            }
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/indices/recovery/RecoveryFilesInfoRequest.java

@@ -92,25 +92,12 @@ public class RecoveryFilesInfoRequest extends RecoveryTransportRequest {
         out.writeLong(recoveryId);
         shardId.writeTo(out);
 
-        out.writeVInt(phase1FileNames.size());
+        out.writeStringCollection(phase1FileNames);
-        for (String phase1FileName : phase1FileNames) {
+        out.writeCollection(phase1FileSizes, StreamOutput::writeVLong);
-            out.writeString(phase1FileName);
-        }
 
-        out.writeVInt(phase1FileSizes.size());
+        out.writeStringCollection(phase1ExistingFileNames);
-        for (Long phase1FileSize : phase1FileSizes) {
+        out.writeCollection(phase1ExistingFileSizes, StreamOutput::writeVLong);
-            out.writeVLong(phase1FileSize);
-        }
 
-        out.writeVInt(phase1ExistingFileNames.size());
-        for (String phase1ExistingFileName : phase1ExistingFileNames) {
-            out.writeString(phase1ExistingFileName);
-        }
-
-        out.writeVInt(phase1ExistingFileSizes.size());
-        for (Long phase1ExistingFileSize : phase1ExistingFileSizes) {
-            out.writeVLong(phase1ExistingFileSize);
-        }
         out.writeVInt(totalTranslogOps);
     }
 }

server/src/main/java/org/elasticsearch/ingest/IngestStats.java

@@ -77,12 +77,11 @@ public class IngestStats implements Writeable, ToXContentFragment {
             if (processorStatsForPipeline == null) {
                 out.writeVInt(0);
             } else {
-                out.writeVInt(processorStatsForPipeline.size());
+                out.writeCollection(processorStatsForPipeline, (o, processorStat) -> {
-                for (ProcessorStat processorStat : processorStatsForPipeline) {
+                    o.writeString(processorStat.getName());
-                    out.writeString(processorStat.getName());
+                    o.writeString(processorStat.getType());
-                    out.writeString(processorStat.getType());
+                    processorStat.getStats().writeTo(o);
-                    processorStat.getStats().writeTo(out);
+                });
-                }
             }
         }
     }

server/src/main/java/org/elasticsearch/monitor/fs/FsInfo.java

@@ -461,10 +461,7 @@ public class FsInfo implements Iterable<FsInfo.Path>, Writeable, ToXContentFragm
     public void writeTo(StreamOutput out) throws IOException {
         out.writeVLong(timestamp);
         out.writeOptionalWriteable(ioStats);
-        out.writeVInt(paths.length);
+        out.writeArray(paths);
-        for (Path path : paths) {
-            path.writeTo(out);
-        }
     }
 
     public Path getTotal() {

server/src/main/java/org/elasticsearch/monitor/jvm/JvmInfo.java

@@ -313,11 +313,7 @@ public class JvmInfo implements ReportingService.Info {
         }
         out.writeString(bootClassPath);
         out.writeString(classPath);
-        out.writeVInt(this.systemProperties.size());
+        out.writeMap(this.systemProperties, StreamOutput::writeString, StreamOutput::writeString);
-        for (Map.Entry<String, String> entry : systemProperties.entrySet()) {
-            out.writeString(entry.getKey());
-            out.writeString(entry.getValue());
-        }
         mem.writeTo(out);
         out.writeStringArray(gcCollectors);
         out.writeStringArray(memoryPools);

server/src/main/java/org/elasticsearch/script/ScriptMetadata.java

@@ -257,12 +257,7 @@ public final class ScriptMetadata implements Metadata.Custom, Writeable, ToXCont
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(scripts.size());
+        out.writeMap(scripts, StreamOutput::writeString, (o, v) -> v.writeTo(o));
-
-        for (Map.Entry<String, StoredScriptSource> entry : scripts.entrySet()) {
-            out.writeString(entry.getKey());
-            entry.getValue().writeTo(out);
-        }
     }
 
     /**

server/src/main/java/org/elasticsearch/search/SearchHit.java

@@ -233,10 +233,7 @@ public final class SearchHit implements Writeable, ToXContentObject, Iterable<Do
         if (fields == null) {
             out.writeVInt(0);
         } else {
-            out.writeVInt(fields.size());
+            out.writeCollection(fields.values());
-            for (DocumentField field : fields.values()) {
-                field.writeTo(out);
-            }
         }
     }
 
@@ -267,30 +264,20 @@ public final class SearchHit implements Writeable, ToXContentObject, Iterable<Do
         if (highlightFields == null) {
             out.writeVInt(0);
         } else {
-            out.writeVInt(highlightFields.size());
+            out.writeCollection(highlightFields.values());
-            for (HighlightField highlightField : highlightFields.values()) {
-                highlightField.writeTo(out);
-            }
         }
         sortValues.writeTo(out);
 
         if (matchedQueries.length == 0) {
             out.writeVInt(0);
         } else {
-            out.writeVInt(matchedQueries.length);
+            out.writeStringArray(matchedQueries);
-            for (String matchedFilter : matchedQueries) {
-                out.writeString(matchedFilter);
-            }
         }
         out.writeOptionalWriteable(shard);
         if (innerHits == null) {
             out.writeVInt(0);
         } else {
-            out.writeVInt(innerHits.size());
+            out.writeMap(innerHits, StreamOutput::writeString, (o, v) -> v.writeTo(o));
-            for (Map.Entry<String, SearchHits> entry : innerHits.entrySet()) {
-                out.writeString(entry.getKey());
-                entry.getValue().writeTo(out);
-            }
         }
     }
 

server/src/main/java/org/elasticsearch/search/SearchHits.java

@@ -97,12 +97,7 @@ public final class SearchHits implements Writeable, ToXContentFragment, Iterable
             Lucene.writeTotalHits(out, totalHits);
         }
         out.writeFloat(maxScore);
-        out.writeVInt(hits.length);
+        out.writeArray(hits);
-        if (hits.length > 0) {
-            for (SearchHit hit : hits) {
-                hit.writeTo(out);
-            }
-        }
         out.writeOptionalArray(Lucene::writeSortField, sortFields);
         out.writeOptionalString(collapseField);
         out.writeOptionalArray(Lucene::writeSortValue, collapseValues);

server/src/main/java/org/elasticsearch/search/aggregations/AggregatorFactories.java

@@ -303,14 +303,8 @@ public class AggregatorFactories {
 
         @Override
         public void writeTo(StreamOutput out) throws IOException {
-            out.writeVInt(this.aggregationBuilders.size());
+            out.writeCollection(this.aggregationBuilders, StreamOutput::writeNamedWriteable);
-            for (AggregationBuilder factory : aggregationBuilders) {
+            out.writeCollection(this.pipelineAggregatorBuilders, StreamOutput::writeNamedWriteable);
-                out.writeNamedWriteable(factory);
-            }
-            out.writeVInt(this.pipelineAggregatorBuilders.size());
-            for (PipelineAggregationBuilder factory : pipelineAggregatorBuilders) {
-                out.writeNamedWriteable(factory);
-            }
         }
 
         public boolean mustVisitAllDocs() {

server/src/main/java/org/elasticsearch/search/aggregations/InternalOrder.java

@@ -519,10 +519,7 @@ public abstract class InternalOrder extends BucketOrder {
                 out.writeBoolean(aggregationOrder.order == SortOrder.ASC);
                 out.writeString(aggregationOrder.path().toString());
             } else if (order instanceof CompoundOrder compoundOrder) {
-                out.writeVInt(compoundOrder.orderElements.size());
+                out.writeCollection(compoundOrder.orderElements);
-                for (BucketOrder innerOrder : compoundOrder.orderElements) {
-                    innerOrder.writeTo(out);
-                }
             }
         }
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/adjacency/InternalAdjacencyMatrix.java

@@ -141,10 +141,7 @@ public class InternalAdjacencyMatrix extends InternalMultiBucketAggregation<Inte
 
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
-        out.writeVInt(buckets.size());
+        out.writeCollection(buckets);
-        for (InternalBucket bucket : buckets) {
-            bucket.writeTo(out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/search/aggregations/bucket/composite/CompositeAggregationBuilder.java

@@ -112,10 +112,7 @@ public class CompositeAggregationBuilder extends AbstractAggregationBuilder<Comp
 
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
-        out.writeVInt(sources.size());
+        out.writeCollection(sources, (o, v) -> CompositeValuesSourceParserHelper.writeTo(v, o));
-        for (CompositeValuesSourceBuilder<?> builder : sources) {
-            CompositeValuesSourceParserHelper.writeTo(builder, out);
-        }
         out.writeVInt(size);
         out.writeBoolean(after != null);
         if (after != null) {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregationBuilder.java

@@ -128,16 +128,7 @@ public class FiltersAggregationBuilder extends AbstractAggregationBuilder<Filter
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeBoolean(keyed);
-        out.writeVInt(filters.size());
+        out.writeCollection(filters, keyed ? (o, v) -> v.writeTo(o) : (o, v) -> o.writeNamedWriteable(v.filter()));
-        if (keyed) {
-            for (KeyedFilter keyedFilter : filters) {
-                keyedFilter.writeTo(out);
-            }
-        } else {
-            for (KeyedFilter keyedFilter : filters) {
-                out.writeNamedWriteable(keyedFilter.filter());
-            }
-        }
         out.writeBoolean(otherBucket);
         out.writeString(otherBucketKey);
     }

server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/InternalFilters.java

@@ -148,10 +148,7 @@ public class InternalFilters extends InternalMultiBucketAggregation<InternalFilt
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeBoolean(keyed);
-        out.writeVInt(buckets.size());
+        out.writeList(buckets);
-        for (InternalBucket bucket : buckets) {
-            bucket.writeTo(out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalAutoDateHistogram.java

@@ -166,10 +166,7 @@ public final class InternalAutoDateHistogram extends InternalMultiBucketAggregat
         }
 
         void writeTo(StreamOutput out) throws IOException {
-            out.writeVInt(roundingInfos.length);
+            out.writeArray(roundingInfos);
-            for (RoundingInfo roundingInfo : roundingInfos) {
-                roundingInfo.writeTo(out);
-            }
             out.writeVInt(roundingIdx);
             emptySubAggregations.writeTo(out);
         }

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/AbstractRangeBuilder.java

@@ -106,10 +106,7 @@ public abstract class AbstractRangeBuilder<AB extends AbstractRangeBuilder<AB, R
 
     @Override
     protected void innerWriteTo(StreamOutput out) throws IOException {
-        out.writeVInt(ranges.size());
+        out.writeList(ranges);
-        for (Range range : ranges) {
-            range.writeTo(out);
-        }
         out.writeBoolean(keyed);
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/GeoDistanceAggregationBuilder.java

@@ -311,10 +311,7 @@ public class GeoDistanceAggregationBuilder extends ValuesSourceAggregationBuilde
     protected void innerWriteTo(StreamOutput out) throws IOException {
         out.writeDouble(origin.lat());
         out.writeDouble(origin.lon());
-        out.writeVInt(ranges.size());
+        out.writeList(ranges);
-        for (Range range : ranges) {
-            range.writeTo(out);
-        }
         out.writeBoolean(keyed);
         distanceType.writeTo(out);
         unit.writeTo(out);

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalRange.java

@@ -302,10 +302,7 @@ public class InternalRange<B extends InternalRange.Bucket, R extends InternalRan
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeNamedWriteable(format);
         out.writeBoolean(keyed);
-        out.writeVInt(ranges.size());
+        out.writeCollection(ranges);
-        for (B bucket : ranges) {
-            bucket.writeTo(out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/IpRangeAggregationBuilder.java

@@ -13,6 +13,7 @@ import org.elasticsearch.Version;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.network.InetAddresses;
 import org.elasticsearch.core.Tuple;
 import org.elasticsearch.script.Script;
@@ -100,7 +101,7 @@ public final class IpRangeAggregationBuilder extends ValuesSourceAggregationBuil
         }
     }
 
-    public static class Range implements ToXContentObject {
+    public static class Range implements ToXContentObject, Writeable {
 
         private final String key;
         private final String from;
@@ -155,7 +156,8 @@ public final class IpRangeAggregationBuilder extends ValuesSourceAggregationBuil
             this.to = in.readOptionalString();
         }
 
-        void writeTo(StreamOutput out) throws IOException {
+        @Override
+        public void writeTo(StreamOutput out) throws IOException {
             out.writeOptionalString(key);
             out.writeOptionalString(from);
             out.writeOptionalString(to);
@@ -354,10 +356,7 @@ public final class IpRangeAggregationBuilder extends ValuesSourceAggregationBuil
 
     @Override
     protected void innerWriteTo(StreamOutput out) throws IOException {
-        out.writeVInt(ranges.size());
+        out.writeCollection(ranges);
-        for (Range range : ranges) {
-            range.writeTo(out);
-        }
         out.writeBoolean(keyed);
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/IncludeExclude.java

@@ -433,18 +433,12 @@ public class IncludeExclude implements Writeable, ToXContentFragment {
         boolean hasIncludes = includeValues != null;
         out.writeBoolean(hasIncludes);
         if (hasIncludes) {
-            out.writeVInt(includeValues.size());
+            out.writeCollection(includeValues, StreamOutput::writeBytesRef);
-            for (BytesRef value : includeValues) {
-                out.writeBytesRef(value);
-            }
         }
         boolean hasExcludes = excludeValues != null;
         out.writeBoolean(hasExcludes);
         if (hasExcludes) {
-            out.writeVInt(excludeValues.size());
+            out.writeCollection(excludeValues, StreamOutput::writeBytesRef);
-            for (BytesRef value : excludeValues) {
-                out.writeBytesRef(value);
-            }
         }
         out.writeVInt(incNumPartitions);
         out.writeVInt(incZeroBasedPartition);

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/BucketScriptPipelineAggregationBuilder.java

@@ -25,7 +25,6 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.Objects;
 import java.util.TreeMap;
 
@@ -96,11 +95,7 @@ public class BucketScriptPipelineAggregationBuilder extends AbstractPipelineAggr
 
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
-        out.writeVInt(bucketsPathsMap.size());
+        out.writeMap(bucketsPathsMap, StreamOutput::writeString, StreamOutput::writeString);
-        for (Entry<String, String> e : bucketsPathsMap.entrySet()) {
-            out.writeString(e.getKey());
-            out.writeString(e.getValue());
-        }
         script.writeTo(out);
         out.writeOptionalString(format);
         gapPolicy.writeTo(out);

server/src/main/java/org/elasticsearch/search/aggregations/support/AggregationInfo.java

@@ -52,14 +52,7 @@ public class AggregationInfo implements ReportingService.Info {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(aggs.size());
+        out.writeMap(aggs, StreamOutput::writeString, StreamOutput::writeStringCollection);
-        for (Map.Entry<String, Set<String>> e : aggs.entrySet()) {
-            out.writeString(e.getKey());
-            out.writeVInt(e.getValue().size());
-            for (String type : e.getValue()) {
-                out.writeString(type);
-            }
-        }
     }
 
     public Map<String, Set<String>> getAggregations() {

server/src/main/java/org/elasticsearch/search/aggregations/timeseries/InternalTimeSeries.java

@@ -181,10 +181,7 @@ public class InternalTimeSeries extends InternalMultiBucketAggregation<InternalT
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeBoolean(keyed);
-        out.writeVInt(buckets.size());
+        out.writeCollection(buckets);
-        for (InternalTimeSeries.InternalBucket bucket : buckets) {
-            bucket.writeTo(out);
-        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/search/builder/SearchSourceBuilder.java

@@ -283,10 +283,7 @@ public final class SearchSourceBuilder implements Writeable, ToXContentObject, R
         boolean hasSorts = sorts != null;
         out.writeBoolean(hasSorts);
         if (hasSorts) {
-            out.writeVInt(sorts.size());
+            out.writeNamedWriteableList(sorts);
-            for (SortBuilder<?> sort : sorts) {
-                out.writeNamedWriteable(sort);
-            }
         }
         boolean hasStats = stats != null;
         out.writeBoolean(hasStats);

server/src/main/java/org/elasticsearch/search/dfs/AggregatedDfs.java

@@ -57,18 +57,14 @@ public class AggregatedDfs implements Writeable {
 
     @Override
     public void writeTo(final StreamOutput out) throws IOException {
-        out.writeVInt(termStatistics.size());
+        out.writeMap(termStatistics, (o, k) -> {
-
+            o.writeString(k.field());
-        for (var entry : termStatistics().entrySet()) {
+            o.writeBytesRef(k.bytes());
-            Term term = entry.getKey();
+        }, (o, v) -> {
-            out.writeString(term.field());
+            o.writeBytesRef(v.term());
-            out.writeBytesRef(term.bytes());
+            o.writeVLong(v.docFreq());
-            TermStatistics stats = entry.getValue();
+            o.writeVLong(DfsSearchResult.addOne(v.totalTermFreq()));
-            out.writeBytesRef(stats.term());
+        });
-            out.writeVLong(stats.docFreq());
-            out.writeVLong(DfsSearchResult.addOne(stats.totalTermFreq()));
-        }
-
         DfsSearchResult.writeFieldStats(out, fieldStatistics);
         out.writeVLong(maxDoc);
     }

server/src/main/java/org/elasticsearch/search/dfs/DfsSearchResult.java

@@ -95,11 +95,10 @@ public class DfsSearchResult extends SearchPhaseResult {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         contextId.writeTo(out);
-        out.writeVInt(terms.length);
+        out.writeArray((o, term) -> {
-        for (Term term : terms) {
+            o.writeString(term.field());
-            out.writeString(term.field());
+            o.writeBytesRef(term.bytes());
-            out.writeBytesRef(term.bytes());
+        }, terms);
-        }
         writeTermStats(out, termStatistics);
         writeFieldStats(out, fieldStatistics);
         out.writeVInt(maxDoc);
@@ -109,25 +108,18 @@ public class DfsSearchResult extends SearchPhaseResult {
     }
 
     public static void writeFieldStats(StreamOutput out, Map<String, CollectionStatistics> fieldStatistics) throws IOException {
-        out.writeVInt(fieldStatistics.size());
+        out.writeMap(fieldStatistics, StreamOutput::writeString, (o, statistics) -> {
-
-        for (var entry : fieldStatistics.entrySet()) {
-            out.writeString(entry.getKey());
-            CollectionStatistics statistics = entry.getValue();
             assert statistics.maxDoc() >= 0;
-            out.writeVLong(statistics.maxDoc());
+            o.writeVLong(statistics.maxDoc());
             // stats are always positive numbers
-            out.writeVLong(statistics.docCount());
+            o.writeVLong(statistics.docCount());
-            out.writeVLong(statistics.sumTotalTermFreq());
+            o.writeVLong(statistics.sumTotalTermFreq());
-            out.writeVLong(statistics.sumDocFreq());
+            o.writeVLong(statistics.sumDocFreq());
-        }
+        });
     }
 
     public static void writeTermStats(StreamOutput out, TermStatistics[] termStatistics) throws IOException {
-        out.writeVInt(termStatistics.length);
+        out.writeArray(DfsSearchResult::writeSingleTermStats, termStatistics);
-        for (TermStatistics termStatistic : termStatistics) {
-            writeSingleTermStats(out, termStatistic);
-        }
     }
 
     public static void writeSingleTermStats(StreamOutput out, TermStatistics termStatistic) throws IOException {

server/src/main/java/org/elasticsearch/search/fetch/ShardFetchRequest.java

@@ -67,10 +67,7 @@ public class ShardFetchRequest extends TransportRequest {
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         contextId.writeTo(out);
-        out.writeVInt(docIds.length);
+        out.writeVIntArray(docIds);
-        for (int docId : docIds) {
-            out.writeVInt(docId);
-        }
         if (lastEmittedDoc == null) {
             out.writeByte((byte) 0);
         } else if (lastEmittedDoc instanceof FieldDoc) {

server/src/main/java/org/elasticsearch/search/fetch/subphase/highlight/HighlightField.java

@@ -94,10 +94,7 @@ public class HighlightField implements ToXContentFragment, Writeable {
             out.writeBoolean(false);
         } else {
             out.writeBoolean(true);
-            out.writeVInt(fragments.length);
+            out.writeArray(StreamOutput::writeText, fragments);
-            for (Text fragment : fragments) {
-                out.writeText(fragment);
-            }
         }
     }
 

server/src/main/java/org/elasticsearch/search/profile/aggregation/AggregationProfileShardResult.java

@@ -50,10 +50,7 @@ public final class AggregationProfileShardResult implements Writeable, ToXConten
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(aggProfileResults.size());
+        out.writeCollection(aggProfileResults);
-        for (ProfileResult p : aggProfileResults) {
-            p.writeTo(out);
-        }
     }
 
     public List<ProfileResult> getProfileResults() {

server/src/main/java/org/elasticsearch/search/searchafter/SearchAfterBuilder.java

@@ -58,10 +58,7 @@ public class SearchAfterBuilder implements ToXContentObject, Writeable {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(sortValues.length);
+        out.writeArray(StreamOutput::writeGenericValue, sortValues);
-        for (Object fieldValue : sortValues) {
-            out.writeGenericValue(fieldValue);
-        }
     }
 
     public SearchAfterBuilder setSortValues(Object[] values) {

server/src/main/java/org/elasticsearch/search/suggest/Suggest.java

@@ -542,10 +542,7 @@ public class Suggest implements Iterable<Suggest.Suggestion<? extends Entry<? ex
                 out.writeText(text);
                 out.writeVInt(offset);
                 out.writeVInt(length);
-                out.writeVInt(options.size());
+                out.writeCollection(options);
-                for (Option option : options) {
-                    option.writeTo(out);
-                }
             }
 
             @Override

server/src/main/java/org/elasticsearch/search/suggest/completion/CompletionSuggestion.java

@@ -411,10 +411,7 @@ public final class CompletionSuggestion extends Suggest.Suggestion<CompletionSug
                 out.writeInt(contexts.size());
                 for (Map.Entry<String, Set<String>> entry : contexts.entrySet()) {
                     out.writeString(entry.getKey());
-                    out.writeVInt(entry.getValue().size());
+                    out.writeStringCollection(entry.getValue());
-                    for (CharSequence ctx : entry.getValue()) {
-                        out.writeString(ctx.toString());
-                    }
                 }
             }
 

server/src/main/java/org/elasticsearch/search/suggest/phrase/PhraseSuggestionBuilder.java

@@ -161,15 +161,7 @@ public class PhraseSuggestionBuilder extends SuggestionBuilder<PhraseSuggestionB
         }
         out.writeMapWithConsistentOrder(collateParams);
         out.writeOptionalBoolean(collatePrune);
-        out.writeVInt(this.generators.size());
+        out.writeMap(this.generators, StreamOutput::writeString, StreamOutput::writeList);
-        for (Entry<String, List<CandidateGenerator>> entry : this.generators.entrySet()) {
-            out.writeString(entry.getKey());
-            List<CandidateGenerator> generatorsList = entry.getValue();
-            out.writeVInt(generatorsList.size());
-            for (CandidateGenerator generator : generatorsList) {
-                generator.writeTo(out);
-            }
-        }
     }
 
     /**

x-pack/plugin/autoscaling/src/main/java/org/elasticsearch/xpack/autoscaling/AutoscalingMetadata.java

@@ -84,10 +84,7 @@ public class AutoscalingMetadata implements Metadata.Custom {
 
     @Override
     public void writeTo(final StreamOutput out) throws IOException {
-        out.writeVInt(policies.size());
+        out.writeCollection(policies.values());
-        for (final Map.Entry<String, AutoscalingPolicyMetadata> policy : policies.entrySet()) {
-            policy.getValue().writeTo(out);
-        }
     }
 
     @Override

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/bulk/BulkShardOperationsRequest.java

@@ -61,10 +61,7 @@ public final class BulkShardOperationsRequest extends ReplicatedWriteRequest<Bul
         super.writeTo(out);
         out.writeString(historyUUID);
         out.writeZLong(maxSeqNoOfUpdatesOrDeletes);
-        out.writeVInt(operations.size());
+        out.writeCollection(operations, Translog.Operation::writeOperation);
-        for (Translog.Operation operation : operations) {
-            Translog.Operation.writeOperation(out, operation);
-        }
     }
 
     @Override

x-pack/plugin/core/src/main/java/org/elasticsearch/license/PostStartBasicResponse.java

@@ -98,14 +98,7 @@ public class PostStartBasicResponse extends AcknowledgedResponse implements Stat
         super.writeTo(out);
         out.writeEnum(status);
         out.writeOptionalString(acknowledgeMessage);
-        out.writeVInt(acknowledgeMessages.size());
+        out.writeMap(acknowledgeMessages, StreamOutput::writeString, StreamOutput::writeStringArray);
-        for (Map.Entry<String, String[]> entry : acknowledgeMessages.entrySet()) {
-            out.writeString(entry.getKey());
-            out.writeVInt(entry.getValue().length);
-            for (String message : entry.getValue()) {
-                out.writeString(message);
-            }
-        }
     }
 
     @Override

x-pack/plugin/core/src/main/java/org/elasticsearch/license/PostStartTrialResponse.java

@@ -88,14 +88,7 @@ public class PostStartTrialResponse extends ActionResponse {
     public void writeTo(StreamOutput out) throws IOException {
         out.writeEnum(status);
         out.writeOptionalString(acknowledgeMessage);
-        out.writeVInt(acknowledgeMessages.size());
+        out.writeMap(acknowledgeMessages, StreamOutput::writeString, StreamOutput::writeStringArray);
-        for (Map.Entry<String, String[]> entry : acknowledgeMessages.entrySet()) {
-            out.writeString(entry.getKey());
-            out.writeVInt(entry.getValue().length);
-            for (String message : entry.getValue()) {
-                out.writeString(message);
-            }
-        }
     }
 
     Map<String, String[]> getAcknowledgementMessages() {

x-pack/plugin/core/src/main/java/org/elasticsearch/protocol/xpack/graph/GraphExploreRequest.java

@@ -15,6 +15,7 @@ import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.search.aggregations.bucket.sampler.SamplerAggregationBuilder;
@@ -313,7 +314,7 @@ public class GraphExploreRequest extends ActionRequest implements IndicesRequest
         return hops.get(hopNumber);
     }
 
-    public static class TermBoost {
+    public static class TermBoost implements Writeable {
         String term;
         float boost;
 
@@ -341,7 +342,8 @@ public class GraphExploreRequest extends ActionRequest implements IndicesRequest
             this.boost = in.readFloat();
         }
 
-        void writeTo(StreamOutput out) throws IOException {
+        @Override
+        public void writeTo(StreamOutput out) throws IOException {
             out.writeString(term);
             out.writeFloat(boost);
         }

x-pack/plugin/core/src/main/java/org/elasticsearch/protocol/xpack/graph/Hop.java

@@ -71,10 +71,7 @@ public class Hop implements ToXContentFragment {
         if (vertices == null) {
             out.writeVInt(0);
         } else {
-            out.writeVInt(vertices.size());
+            out.writeList(vertices);
-            for (VertexRequest vr : vertices) {
-                vr.writeTo(out);
-            }
         }
     }
 

x-pack/plugin/core/src/main/java/org/elasticsearch/protocol/xpack/graph/VertexRequest.java

@@ -9,6 +9,7 @@ package org.elasticsearch.protocol.xpack.graph;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.protocol.xpack.graph.GraphExploreRequest.TermBoost;
 import org.elasticsearch.xcontent.ToXContentObject;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -27,7 +28,7 @@ import java.util.TreeSet;
  * inclusion list to filter which terms are considered.
  *
  */
-public class VertexRequest implements ToXContentObject {
+public class VertexRequest implements ToXContentObject, Writeable {
     public static final int DEFAULT_SIZE = 5;
     public static final int DEFAULT_MIN_DOC_COUNT = 3;
     public static final int DEFAULT_SHARD_MIN_DOC_COUNT = 2;
@@ -69,26 +70,21 @@ public class VertexRequest implements ToXContentObject {
 
     }
 
-    void writeTo(StreamOutput out) throws IOException {
+    @Override
+    public void writeTo(StreamOutput out) throws IOException {
         out.writeString(fieldName);
         out.writeVInt(size);
         out.writeVInt(minDocCount);
         out.writeVInt(shardMinDocCount);
 
         if (includes != null) {
-            out.writeVInt(includes.size());
+            out.writeCollection(includes.values());
-            for (TermBoost tb : includes.values()) {
-                tb.writeTo(out);
-            }
         } else {
             out.writeVInt(0);
         }
 
         if (excludes != null) {
-            out.writeVInt(excludes.size());
+            out.writeStringCollection(excludes);
-            for (String term : excludes) {
-                out.writeString(term);
-            }
         } else {
             out.writeVInt(0);
         }

x-pack/plugin/core/src/main/java/org/elasticsearch/protocol/xpack/license/PutLicenseResponse.java

@@ -76,14 +76,7 @@ public class PutLicenseResponse extends AcknowledgedResponse {
         super.writeTo(out);
         out.writeVInt(status.id());
         out.writeOptionalString(acknowledgeHeader);
-        out.writeVInt(acknowledgeMessages.size());
+        out.writeMap(acknowledgeMessages, StreamOutput::writeString, StreamOutput::writeStringArray);
-        for (Map.Entry<String, String[]> entry : acknowledgeMessages.entrySet()) {
-            out.writeString(entry.getKey());
-            out.writeVInt(entry.getValue().length);
-            for (String message : entry.getValue()) {
-                out.writeString(message);
-            }
-        }
     }
 
     @Override

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/ExplainLifecycleResponse.java

@@ -96,10 +96,7 @@ public class ExplainLifecycleResponse extends ActionResponse implements ToXConte
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(indexResponses.size());
+        out.writeCollection(indexResponses.values());
-        for (IndexLifecycleExplainResponse e : indexResponses.values()) {
-            e.writeTo(out);
-        }
     }
 
     @Override

x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/exporter/ExportException.java

@@ -55,10 +55,7 @@ public class ExportException extends ElasticsearchException implements Iterable<
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        out.writeVInt(exceptions.size());
+        out.writeCollection(exceptions);
-        for (ExportException e : exceptions) {
-            e.writeTo(out);
-        }
     }
 
     @Override

x-pack/plugin/sql/sql-action/src/main/java/org/elasticsearch/xpack/sql/action/AbstractSqlQueryRequest.java

@@ -455,10 +455,7 @@ public abstract class AbstractSqlQueryRequest extends AbstractSqlRequest impleme
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         out.writeString(query);
-        out.writeVInt(params.size());
+        out.writeCollection(params, AbstractSqlQueryRequest::writeSqlTypedParamValue);
-        for (SqlTypedParamValue param : params) {
-            writeSqlTypedParamValue(out, param);
-        }
         out.writeZoneId(zoneId);
         if (out.getVersion().onOrAfter(Version.V_7_16_0)) {
             out.writeOptionalString(catalog);