Liberalize StreamOutput#writeStringList (#37768)

In some cases we only have a string collection instead of a string list
that we want to serialize out. We have a convenience method for writing
a list of strings, but no such method for writing a collection of
strings. Yet, a list of strings is a collection of strings, so we can
simply liberalize StreamOutput#writeStringList to be more generous in
the collections that it accepts and write out collections of strings
too. On the other side, we do not have a convenience method for reading
a list of strings. This commit addresses both of these issues.

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

@@ -461,7 +461,7 @@ public class PutIndexTemplateRequest extends MasterNodeRequest<PutIndexTemplateR
         name = in.readString();
 
         if (in.getVersion().onOrAfter(Version.V_6_0_0_alpha1)) {
-            indexPatterns = in.readList(StreamInput::readString);
+            indexPatterns = in.readStringList();
         } else {
             indexPatterns = Collections.singletonList(in.readString());
         }
@@ -495,7 +495,7 @@ public class PutIndexTemplateRequest extends MasterNodeRequest<PutIndexTemplateR
         out.writeString(cause);
         out.writeString(name);
         if (out.getVersion().onOrAfter(Version.V_6_0_0_alpha1)) {
-            out.writeStringList(indexPatterns);
+            out.writeStringCollection(indexPatterns);
         } else {
             out.writeString(indexPatterns.size() > 0 ? indexPatterns.get(0) : "");
         }

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

@@ -189,7 +189,7 @@ public class IndexTemplateMetaData extends AbstractDiffable<IndexTemplateMetaDat
         Builder builder = new Builder(in.readString());
         builder.order(in.readInt());
         if (in.getVersion().onOrAfter(Version.V_6_0_0_alpha1)) {
-            builder.patterns(in.readList(StreamInput::readString));
+            builder.patterns(in.readStringList());
         } else {
             builder.patterns(Collections.singletonList(in.readString()));
         }
@@ -224,7 +224,7 @@ public class IndexTemplateMetaData extends AbstractDiffable<IndexTemplateMetaDat
         out.writeString(name);
         out.writeInt(order);
         if (out.getVersion().onOrAfter(Version.V_6_0_0_alpha1)) {
-            out.writeStringList(patterns);
+            out.writeStringCollection(patterns);
         } else {
             out.writeString(patterns.get(0));
         }

server/src/main/java/org/elasticsearch/common/io/stream/StreamInput.java

@@ -946,12 +946,26 @@ public abstract class StreamInput extends InputStream {
     }
 
     /**
-     * Reads a list of objects
+     * Reads a list of objects. The list is expected to have been written using {@link StreamOutput#writeList(List)} or
+     * {@link StreamOutput#writeStreamableList(List)}.
+     *
+     * @return the list of objects
+     * @throws IOException if an I/O exception occurs reading the list
      */
-    public <T> List<T> readList(Writeable.Reader<T> reader) throws IOException {
+    public <T> List<T> readList(final Writeable.Reader<T> reader) throws IOException {
         return readCollection(reader, ArrayList::new);
     }
 
+    /**
+     * Reads a list of strings. The list is expected to have been written using {@link StreamOutput#writeStringCollection(Collection)}.
+     *
+     * @return the list of strings
+     * @throws IOException if an I/O exception occurs reading the list
+     */
+    public List<String> readStringList() throws IOException {
+        return readList(StreamInput::readString);
+    }
+
     /**
      * Reads a set of objects
      */

server/src/main/java/org/elasticsearch/common/io/stream/StreamOutput.java

@@ -1048,23 +1048,27 @@ public abstract class StreamOutput extends OutputStream {
     }
 
     /**
-     * Writes a collection of generic objects via a {@link Writer}
+     * Writes a collection of objects via a {@link Writer}.
+     *
+     * @param collection the collection of objects
+     * @throws IOException if an I/O exception occurs writing the collection
      */
-    public <T> void writeCollection(Collection<T> collection, Writer<T> writer) throws IOException {
+    public <T> void writeCollection(final Collection<T> collection, final Writer<T> writer) throws IOException {
         writeVInt(collection.size());
-        for (T val: collection) {
+        for (final T val: collection) {
             writer.write(this, val);
         }
     }
 
     /**
-     * Writes a list of strings
+     * Writes a collection of a strings. The corresponding collection can be read from a stream input using
+     * {@link StreamInput#readList(Writeable.Reader)}.
+     *
+     * @param collection the collection of strings
+     * @throws IOException if an I/O exception occurs writing the collection
      */
-    public void writeStringList(List<String> list) throws IOException {
+    public void writeStringCollection(final Collection<String> collection) throws IOException {
-        writeVInt(list.size());
+        writeCollection(collection, StreamOutput::writeString);
-        for (String string: list) {
-            this.writeString(string);
-        }
     }
 
     /**

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

@@ -60,9 +60,9 @@ public final class RecoveryResponse extends TransportResponse {
 
     RecoveryResponse(StreamInput in) throws IOException {
         super(in);
-        phase1FileNames = in.readList(StreamInput::readString);
+        phase1FileNames = in.readStringList();
         phase1FileSizes = in.readList(StreamInput::readVLong);
-        phase1ExistingFileNames = in.readList(StreamInput::readString);
+        phase1ExistingFileNames = in.readStringList();
         phase1ExistingFileSizes = in.readList(StreamInput::readVLong);
         phase1TotalSize = in.readVLong();
         phase1ExistingTotalSize = in.readVLong();
@@ -76,9 +76,9 @@ public final class RecoveryResponse extends TransportResponse {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        out.writeStringList(phase1FileNames);
+        out.writeStringCollection(phase1FileNames);
         out.writeCollection(phase1FileSizes, StreamOutput::writeVLong);
-        out.writeStringList(phase1ExistingFileNames);
+        out.writeStringCollection(phase1ExistingFileNames);
         out.writeCollection(phase1ExistingFileSizes, StreamOutput::writeVLong);
         out.writeVLong(phase1TotalSize);
         out.writeVLong(phase1ExistingTotalSize);

server/src/main/java/org/elasticsearch/plugins/PluginInfo.java

@@ -103,7 +103,7 @@ public class PluginInfo implements Writeable, ToXContentObject {
         }
         this.classname = in.readString();
         if (in.getVersion().onOrAfter(Version.V_6_2_0)) {
-            extendedPlugins = in.readList(StreamInput::readString);
+            extendedPlugins = in.readStringList();
         } else {
             extendedPlugins = Collections.emptyList();
         }
@@ -128,7 +128,7 @@ public class PluginInfo implements Writeable, ToXContentObject {
         }
         out.writeString(classname);
         if (out.getVersion().onOrAfter(Version.V_6_2_0)) {
-            out.writeStringList(extendedPlugins);
+            out.writeStringCollection(extendedPlugins);
         }
         out.writeBoolean(hasNativeController);
         if (out.getVersion().onOrAfter(Version.V_6_0_0_beta2) && out.getVersion().before(Version.V_6_3_0)) {

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

@@ -69,7 +69,7 @@ public class InternalComposite
     public InternalComposite(StreamInput in) throws IOException {
         super(in);
         this.size = in.readVInt();
-        this.sourceNames = in.readList(StreamInput::readString);
+        this.sourceNames = in.readStringList();
         this.formats = new ArrayList<>(sourceNames.size());
         for (int i = 0; i < sourceNames.size(); i++) {
             if (in.getVersion().onOrAfter(Version.V_6_3_0)) {
@@ -90,7 +90,7 @@ public class InternalComposite
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeVInt(size);
-        out.writeStringList(sourceNames);
+        out.writeStringCollection(sourceNames);
         if (out.getVersion().onOrAfter(Version.V_6_3_0)) {
             for (DocValueFormat format : formats) {
                 out.writeNamedWriteable(format);

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

@@ -243,7 +243,7 @@ public final class SearchSourceBuilder implements Writeable, ToXContentObject, R
             }
         }
         if (in.readBoolean()) {
-            stats = in.readList(StreamInput::readString);
+            stats = in.readStringList();
         }
         suggestBuilder = in.readOptionalWriteable(SuggestBuilder::new);
         terminateAfter = in.readVInt();
@@ -311,7 +311,7 @@ public final class SearchSourceBuilder implements Writeable, ToXContentObject, R
         boolean hasStats = stats != null;
         out.writeBoolean(hasStats);
         if (hasStats) {
-            out.writeStringList(stats);
+            out.writeStringCollection(stats);
         }
         out.writeOptionalWriteable(suggestBuilder);
         out.writeVInt(terminateAfter);

server/src/test/java/org/elasticsearch/common/io/stream/StreamTests.java

@@ -20,6 +20,8 @@
 package org.elasticsearch.common.io.stream;
 
 import org.apache.lucene.util.BytesRef;
+import org.elasticsearch.common.CheckedBiConsumer;
+import org.elasticsearch.common.CheckedFunction;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.collect.Tuple;
@@ -39,6 +41,7 @@ import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 
@@ -293,15 +296,27 @@ public class StreamTests extends ESTestCase {
 
         }
 
-        final int length = randomIntBetween(0, 16);
+        runWriteReadCollectionTest(
-        final Collection<FooBar> fooBars = new ArrayList<>(length);
+                () -> new FooBar(randomInt(), randomInt()), StreamOutput::writeCollection, in -> in.readList(FooBar::new));
+    }
+
+    public void testStringCollection() throws IOException {
+        runWriteReadCollectionTest(() -> randomUnicodeOfLength(16), StreamOutput::writeStringCollection, StreamInput::readStringList);
+    }
+
+    private <T> void runWriteReadCollectionTest(
+            final Supplier<T> supplier,
+            final CheckedBiConsumer<StreamOutput, Collection<T>, IOException> writer,
+            final CheckedFunction<StreamInput, Collection<T>, IOException> reader) throws IOException {
+        final int length = randomIntBetween(0, 10);
+        final Collection<T> collection = new ArrayList<>(length);
         for (int i = 0; i < length; i++) {
-            fooBars.add(new FooBar(randomInt(), randomInt()));
+            collection.add(supplier.get());
         }
         try (BytesStreamOutput out = new BytesStreamOutput()) {
-            out.writeCollection(fooBars);
+            writer.accept(out, collection);
             try (StreamInput in = out.bytes().streamInput()) {
-                assertThat(fooBars, equalTo(in.readList(FooBar::new)));
+                assertThat(collection, equalTo(reader.apply(in)));
             }
         }
     }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowMetadata.java

@@ -273,7 +273,7 @@ public class AutoFollowMetadata extends AbstractNamedDiffable<MetaData.Custom> i
 
         public AutoFollowPattern(StreamInput in) throws IOException {
             remoteCluster = in.readString();
-            leaderIndexPatterns = in.readList(StreamInput::readString);
+            leaderIndexPatterns = in.readStringList();
             followIndexPattern = in.readOptionalString();
             maxReadRequestOperationCount = in.readOptionalVInt();
             maxReadRequestSize = in.readOptionalWriteable(ByteSizeValue::new);
@@ -350,7 +350,7 @@ public class AutoFollowMetadata extends AbstractNamedDiffable<MetaData.Custom> i
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeString(remoteCluster);
-            out.writeStringList(leaderIndexPatterns);
+            out.writeStringCollection(leaderIndexPatterns);
             out.writeOptionalString(followIndexPattern);
             out.writeOptionalVInt(maxReadRequestOperationCount);
             out.writeOptionalWriteable(maxReadRequestSize);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/action/PutAutoFollowPatternAction.java

@@ -275,7 +275,7 @@ public class PutAutoFollowPatternAction extends Action<AcknowledgedResponse> {
             super(in);
             name = in.readString();
             remoteCluster = in.readString();
-            leaderIndexPatterns = in.readList(StreamInput::readString);
+            leaderIndexPatterns = in.readStringList();
             followIndexNamePattern = in.readOptionalString();
             maxReadRequestOperationCount = in.readOptionalVInt();
             maxReadRequestSize = in.readOptionalWriteable(ByteSizeValue::new);
@@ -294,7 +294,7 @@ public class PutAutoFollowPatternAction extends Action<AcknowledgedResponse> {
             super.writeTo(out);
             out.writeString(name);
             out.writeString(remoteCluster);
-            out.writeStringList(leaderIndexPatterns);
+            out.writeStringCollection(leaderIndexPatterns);
             out.writeOptionalString(followIndexNamePattern);
             out.writeOptionalVInt(maxReadRequestOperationCount);
             out.writeOptionalWriteable(maxReadRequestSize);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/action/RemoveIndexLifecyclePolicyAction.java

@@ -82,13 +82,13 @@ public class RemoveIndexLifecyclePolicyAction extends Action<RemoveIndexLifecycl
         @Override
         public void readFrom(StreamInput in) throws IOException {
             super.readFrom(in);
-            failedIndexes = in.readList(StreamInput::readString);
+            failedIndexes = in.readStringList();
         }
 
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             super.writeTo(out);
-            out.writeStringList(failedIndexes);
+            out.writeStringCollection(failedIndexes);
         }
 
         @Override

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/FindFileStructureAction.java

@@ -327,7 +327,7 @@ public class FindFileStructureAction extends Action<FindFileStructureAction.Resp
             timeout = in.readOptionalTimeValue();
             charset = in.readOptionalString();
             format = in.readBoolean() ? in.readEnum(FileStructure.Format.class) : null;
-            columnNames = in.readBoolean() ? in.readList(StreamInput::readString) : null;
+            columnNames = in.readBoolean() ? in.readStringList() : null;
             hasHeaderRow = in.readOptionalBoolean();
             delimiter = in.readBoolean() ? (char) in.readVInt() : null;
             quote = in.readBoolean() ? (char) in.readVInt() : null;

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/GetJobsStatsAction.java

@@ -84,7 +84,7 @@ public class GetJobsStatsAction extends Action<GetJobsStatsAction.Response> {
         public Request(StreamInput in) throws IOException {
             super(in);
             jobId = in.readString();
-            expandedJobsIds = in.readList(StreamInput::readString);
+            expandedJobsIds = in.readStringList();
             if (in.getVersion().onOrAfter(Version.V_6_1_0)) {
                 allowNoJobs = in.readBoolean();
             }
@@ -94,7 +94,7 @@ public class GetJobsStatsAction extends Action<GetJobsStatsAction.Response> {
         public void writeTo(StreamOutput out) throws IOException {
             super.writeTo(out);
             out.writeString(jobId);
-            out.writeStringList(expandedJobsIds);
+            out.writeStringCollection(expandedJobsIds);
             if (out.getVersion().onOrAfter(Version.V_6_1_0)) {
                 out.writeBoolean(allowNoJobs);
             }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/StartDatafeedAction.java

@@ -197,7 +197,7 @@ public class StartDatafeedAction extends Action<AcknowledgedResponse> {
             timeout = TimeValue.timeValueMillis(in.readVLong());
             if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
                 jobId = in.readOptionalString();
-                datafeedIndices = in.readList(StreamInput::readString);
+                datafeedIndices = in.readStringList();
             }
         }
 
@@ -274,7 +274,7 @@ public class StartDatafeedAction extends Action<AcknowledgedResponse> {
             out.writeVLong(timeout.millis());
             if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
                 out.writeOptionalString(jobId);
-                out.writeStringList(datafeedIndices);
+                out.writeStringCollection(datafeedIndices);
             }
         }
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedConfig.java

@@ -246,14 +246,14 @@ public class DatafeedConfig extends AbstractDiffable<DatafeedConfig> implements
         this.queryDelay = in.readOptionalTimeValue();
         this.frequency = in.readOptionalTimeValue();
         if (in.readBoolean()) {
-            this.indices = Collections.unmodifiableList(in.readList(StreamInput::readString));
+            this.indices = Collections.unmodifiableList(in.readStringList());
         } else {
             this.indices = null;
         }
         // This consumes the list of types if there was one.
         if (in.getVersion().before(Version.V_7_0_0)) {
             if (in.readBoolean()) {
-                in.readList(StreamInput::readString);
+                in.readStringList();
             }
         }
         if (in.getVersion().before(Version.V_6_6_0)) {
@@ -408,7 +408,7 @@ public class DatafeedConfig extends AbstractDiffable<DatafeedConfig> implements
         out.writeOptionalTimeValue(frequency);
         if (indices != null) {
             out.writeBoolean(true);
-            out.writeStringList(indices);
+            out.writeStringCollection(indices);
         } else {
             out.writeBoolean(false);
         }
@@ -416,7 +416,7 @@ public class DatafeedConfig extends AbstractDiffable<DatafeedConfig> implements
         // An empty list is expected
         if (out.getVersion().before(Version.V_7_0_0)) {
             out.writeBoolean(true);
-            out.writeStringList(Collections.emptyList());
+            out.writeStringCollection(Collections.emptyList());
         }
         if (out.getVersion().before(Version.V_6_6_0)) {
             out.writeNamedWriteable(getParsedQuery());

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedUpdate.java

@@ -107,14 +107,14 @@ public class DatafeedUpdate implements Writeable, ToXContentObject {
         this.queryDelay = in.readOptionalTimeValue();
         this.frequency = in.readOptionalTimeValue();
         if (in.readBoolean()) {
-            this.indices = in.readList(StreamInput::readString);
+            this.indices = in.readStringList();
         } else {
             this.indices = null;
         }
         // This consumes the list of types if there was one.
         if (in.getVersion().before(Version.V_7_0_0)) {
             if (in.readBoolean()) {
-                in.readList(StreamInput::readString);
+                in.readStringList();
             }
         }
         this.query = in.readOptionalNamedWriteable(QueryBuilder.class);
@@ -148,7 +148,7 @@ public class DatafeedUpdate implements Writeable, ToXContentObject {
         out.writeOptionalTimeValue(frequency);
         if (indices != null) {
             out.writeBoolean(true);
-            out.writeStringList(indices);
+            out.writeStringCollection(indices);
         } else {
             out.writeBoolean(false);
         }
@@ -156,7 +156,7 @@ public class DatafeedUpdate implements Writeable, ToXContentObject {
         // An empty list is expected
         if (out.getVersion().before(Version.V_7_0_0)) {
             out.writeBoolean(true);
-            out.writeStringList(Collections.emptyList());
+            out.writeStringCollection(Collections.emptyList());
         }
         out.writeOptionalNamedWriteable(query);
         out.writeOptionalWriteable(aggregations);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/filestructurefinder/FileStructure.java

@@ -206,20 +206,20 @@ public class FileStructure implements ToXContentObject, Writeable {
         format = in.readEnum(Format.class);
         multilineStartPattern = in.readOptionalString();
         excludeLinesPattern = in.readOptionalString();
-        columnNames = in.readBoolean() ? Collections.unmodifiableList(in.readList(StreamInput::readString)) : null;
+        columnNames = in.readBoolean() ? Collections.unmodifiableList(in.readStringList()) : null;
         hasHeaderRow = in.readOptionalBoolean();
         delimiter = in.readBoolean() ? (char) in.readVInt() : null;
         quote = in.readBoolean() ? (char) in.readVInt() : null;
         shouldTrimFields = in.readOptionalBoolean();
         grokPattern = in.readOptionalString();
-        jodaTimestampFormats = in.readBoolean() ? Collections.unmodifiableList(in.readList(StreamInput::readString)) : null;
+        jodaTimestampFormats = in.readBoolean() ? Collections.unmodifiableList(in.readStringList()) : null;
-        javaTimestampFormats = in.readBoolean() ? Collections.unmodifiableList(in.readList(StreamInput::readString)) : null;
+        javaTimestampFormats = in.readBoolean() ? Collections.unmodifiableList(in.readStringList()) : null;
         timestampField = in.readOptionalString();
         needClientTimezone = in.readBoolean();
         mappings = Collections.unmodifiableSortedMap(new TreeMap<>(in.readMap()));
         ingestPipeline = in.readBoolean() ? Collections.unmodifiableMap(in.readMap()) : null;
         fieldStats = Collections.unmodifiableSortedMap(new TreeMap<>(in.readMap(StreamInput::readString, FieldStats::new)));
-        explanation = Collections.unmodifiableList(in.readList(StreamInput::readString));
+        explanation = Collections.unmodifiableList(in.readStringList());
     }
 
     @Override

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/AnalysisConfig.java

@@ -125,7 +125,7 @@ public class AnalysisConfig implements ToXContentObject, Writeable {
     public AnalysisConfig(StreamInput in) throws IOException {
         bucketSpan = in.readTimeValue();
         categorizationFieldName = in.readOptionalString();
-        categorizationFilters = in.readBoolean() ? Collections.unmodifiableList(in.readList(StreamInput::readString)) : null;
+        categorizationFilters = in.readBoolean() ? Collections.unmodifiableList(in.readStringList()) : null;
         if (in.getVersion().onOrAfter(Version.V_6_2_0)) {
             categorizationAnalyzerConfig = in.readOptionalWriteable(CategorizationAnalyzerConfig::new);
         } else {
@@ -134,7 +134,7 @@ public class AnalysisConfig implements ToXContentObject, Writeable {
         latency = in.readOptionalTimeValue();
         summaryCountFieldName = in.readOptionalString();
         detectors = Collections.unmodifiableList(in.readList(Detector::new));
-        influencers = Collections.unmodifiableList(in.readList(StreamInput::readString));
+        influencers = Collections.unmodifiableList(in.readStringList());
 
         multivariateByFields = in.readOptionalBoolean();
     }
@@ -145,7 +145,7 @@ public class AnalysisConfig implements ToXContentObject, Writeable {
         out.writeOptionalString(categorizationFieldName);
         if (categorizationFilters != null) {
             out.writeBoolean(true);
-            out.writeStringList(categorizationFilters);
+            out.writeStringCollection(categorizationFilters);
         } else {
             out.writeBoolean(false);
         }
@@ -155,7 +155,7 @@ public class AnalysisConfig implements ToXContentObject, Writeable {
         out.writeOptionalTimeValue(latency);
         out.writeOptionalString(summaryCountFieldName);
         out.writeList(detectors);
-        out.writeStringList(influencers);
+        out.writeStringCollection(influencers);
 
         out.writeOptionalBoolean(multivariateByFields);
     }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/Job.java

@@ -187,7 +187,7 @@ public class Job extends AbstractDiffable<Job> implements Writeable, ToXContentO
         jobType = in.readString();
         jobVersion = in.readBoolean() ? Version.readVersion(in) : null;
         if (in.getVersion().onOrAfter(Version.V_6_1_0)) {
-            groups = Collections.unmodifiableList(in.readList(StreamInput::readString));
+            groups = Collections.unmodifiableList(in.readStringList());
         } else {
             groups = Collections.emptyList();
         }
@@ -444,7 +444,7 @@ public class Job extends AbstractDiffable<Job> implements Writeable, ToXContentO
             out.writeBoolean(false);
         }
         if (out.getVersion().onOrAfter(Version.V_6_1_0)) {
-            out.writeStringList(groups);
+            out.writeStringCollection(groups);
         }
         out.writeOptionalString(description);
         out.writeVLong(createTime.getTime());
@@ -671,7 +671,7 @@ public class Job extends AbstractDiffable<Job> implements Writeable, ToXContentO
             jobType = in.readString();
             jobVersion = in.readBoolean() ? Version.readVersion(in) : null;
             if (in.getVersion().onOrAfter(Version.V_6_1_0)) {
-                groups = in.readList(StreamInput::readString);
+                groups = in.readStringList();
             } else {
                 groups = Collections.emptyList();
             }
@@ -856,7 +856,7 @@ public class Job extends AbstractDiffable<Job> implements Writeable, ToXContentO
                 out.writeBoolean(false);
             }
             if (out.getVersion().onOrAfter(Version.V_6_1_0)) {
-                out.writeStringList(groups);
+                out.writeStringCollection(groups);
             }
             out.writeOptionalString(description);
             if (createTime != null) {

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/JobUpdate.java

@@ -125,7 +125,7 @@ public class JobUpdate implements Writeable, ToXContentObject {
         modelSnapshotRetentionDays = in.readOptionalLong();
         resultsRetentionDays = in.readOptionalLong();
         if (in.readBoolean()) {
-            categorizationFilters = in.readList(StreamInput::readString);
+            categorizationFilters = in.readStringList();
         } else {
             categorizationFilters = null;
         }
@@ -172,7 +172,7 @@ public class JobUpdate implements Writeable, ToXContentObject {
         out.writeOptionalLong(resultsRetentionDays);
         out.writeBoolean(categorizationFilters != null);
         if (categorizationFilters != null) {
-            out.writeStringList(categorizationFilters);
+            out.writeStringCollection(categorizationFilters);
         }
         out.writeMap(customSettings);
         out.writeOptionalString(modelSnapshotId);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/Bucket.java

@@ -139,7 +139,7 @@ public class Bucket implements ToXContentObject, Writeable {
             in.readList(Bucket::readOldPerPartitionNormalization);
         }
         if (in.getVersion().onOrAfter(Version.V_6_2_0)) {
-            scheduledEvents = in.readList(StreamInput::readString);
+            scheduledEvents = in.readStringList();
             if (scheduledEvents.isEmpty()) {
                 scheduledEvents = Collections.emptyList();
             }
@@ -165,7 +165,7 @@ public class Bucket implements ToXContentObject, Writeable {
             out.writeList(Collections.emptyList());
         }
         if (out.getVersion().onOrAfter(Version.V_6_2_0)) {
-            out.writeStringList(scheduledEvents);
+            out.writeStringCollection(scheduledEvents);
         }
     }
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/CategoryDefinition.java

@@ -77,7 +77,7 @@ public class CategoryDefinition implements ToXContentObject, Writeable {
         terms = in.readString();
         regex = in.readString();
         maxMatchingLength = in.readLong();
-        examples = new TreeSet<>(in.readList(StreamInput::readString));
+        examples = new TreeSet<>(in.readStringList());
         if (in.getVersion().onOrAfter(Version.V_6_4_0)) {
             grokPattern = in.readOptionalString();
         }
@@ -90,7 +90,7 @@ public class CategoryDefinition implements ToXContentObject, Writeable {
         out.writeString(terms);
         out.writeString(regex);
         out.writeLong(maxMatchingLength);
-        out.writeStringList(new ArrayList<>(examples));
+        out.writeStringCollection(examples);
         if (out.getVersion().onOrAfter(Version.V_6_4_0)) {
             out.writeOptionalString(grokPattern);
         }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/ForecastRequestStats.java

@@ -124,7 +124,7 @@ public class ForecastRequestStats implements ToXContentObject, Writeable {
         forecastId = in.readString();
         recordCount = in.readLong();
         if (in.readBoolean()) {
-            messages = in.readList(StreamInput::readString);
+            messages = in.readStringList();
         } else {
             messages = null;
         }
@@ -147,7 +147,7 @@ public class ForecastRequestStats implements ToXContentObject, Writeable {
         out.writeLong(recordCount);
         if (messages != null) {
             out.writeBoolean(true);
-            out.writeStringList(messages);
+            out.writeStringCollection(messages);
         } else {
             out.writeBoolean(false);
         }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/rollup/job/MetricConfig.java

@@ -86,7 +86,7 @@ public class MetricConfig implements Writeable, ToXContentObject {
 
     MetricConfig(final StreamInput in) throws IOException {
         field = in.readString();
-        metrics = in.readList(StreamInput::readString);
+        metrics = in.readStringList();
     }
 
     /**
@@ -144,7 +144,7 @@ public class MetricConfig implements Writeable, ToXContentObject {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeString(field);
-        out.writeStringList(metrics);
+        out.writeStringCollection(metrics);
     }
 
     @Override

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/privilege/PutPrivilegesResponse.java

@@ -49,12 +49,12 @@ public final class PutPrivilegesResponse extends ActionResponse implements ToXCo
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        out.writeMap(created, StreamOutput::writeString, StreamOutput::writeStringList);
+        out.writeMap(created, StreamOutput::writeString, StreamOutput::writeStringCollection);
     }
 
     @Override
     public void readFrom(StreamInput in) throws IOException {
         super.readFrom(in);
-        this.created = Collections.unmodifiableMap(in.readMap(StreamInput::readString, si -> si.readList(StreamInput::readString)));
+        this.created = Collections.unmodifiableMap(in.readMap(StreamInput::readString, StreamInput::readStringList));
     }
 }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/rolemapping/PutRoleMappingRequest.java

@@ -125,7 +125,7 @@ public class PutRoleMappingRequest extends ActionRequest
         super.readFrom(in);
         this.name = in.readString();
         this.enabled = in.readBoolean();
-        this.roles = in.readList(StreamInput::readString);
+        this.roles = in.readStringList();
         this.rules = ExpressionParser.readExpression(in);
         this.metadata = in.readMap();
         this.refreshPolicy = RefreshPolicy.readFrom(in);
@@ -136,7 +136,7 @@ public class PutRoleMappingRequest extends ActionRequest
         super.writeTo(out);
         out.writeString(name);
         out.writeBoolean(enabled);
-        out.writeStringList(roles);
+        out.writeStringCollection(roles);
         ExpressionParser.writeExpression(rules, out);
         out.writeMap(metadata);
         refreshPolicy.writeTo(out);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authc/support/TokensInvalidationResult.java

@@ -49,8 +49,8 @@ public class TokensInvalidationResult implements ToXContentObject, Writeable {
     }
 
     public TokensInvalidationResult(StreamInput in) throws IOException {
-        this.invalidatedTokens = in.readList(StreamInput::readString);
+        this.invalidatedTokens = in.readStringList();
-        this.previouslyInvalidatedTokens = in.readList(StreamInput::readString);
+        this.previouslyInvalidatedTokens = in.readStringList();
         this.errors = in.readList(StreamInput::readException);
         this.attemptCount = in.readVInt();
     }
@@ -97,8 +97,8 @@ public class TokensInvalidationResult implements ToXContentObject, Writeable {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeStringList(invalidatedTokens);
+        out.writeStringCollection(invalidatedTokens);
-        out.writeStringList(previouslyInvalidatedTokens);
+        out.writeStringCollection(previouslyInvalidatedTokens);
         out.writeCollection(errors, StreamOutput::writeException);
         out.writeVInt(attemptCount);
     }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authc/support/mapper/ExpressionRoleMapping.java

@@ -78,7 +78,7 @@ public class ExpressionRoleMapping implements ToXContentObject, Writeable {
     public ExpressionRoleMapping(StreamInput in) throws IOException {
         this.name = in.readString();
         this.enabled = in.readBoolean();
-        this.roles = in.readList(StreamInput::readString);
+        this.roles = in.readStringList();
         this.expression = ExpressionParser.readExpression(in);
         this.metadata = in.readMap();
     }
@@ -87,7 +87,7 @@ public class ExpressionRoleMapping implements ToXContentObject, Writeable {
     public void writeTo(StreamOutput out) throws IOException {
         out.writeString(name);
         out.writeBoolean(enabled);
-        out.writeStringList(roles);
+        out.writeStringCollection(roles);
         ExpressionParser.writeExpression(expression, out);
         out.writeMap(metadata);
     }