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

@@ -462,7 +462,7 @@ public void readFrom(StreamInput in) throws IOException {
         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());
         }
@@ -501,7 +501,7 @@ public void writeTo(StreamOutput out) throws IOException {
         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

@@ -198,7 +198,7 @@ public static IndexTemplateMetaData readFrom(StreamInput in) throws IOException
         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()));
         }
@@ -235,7 +235,7 @@ public void writeTo(StreamOutput out) throws IOException {
         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

@@ -935,12 +935,26 @@ public <T extends Streamable> List<T> readStreamableList(Supplier<T> constructor
     }
 
     /**
-     * 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

@@ -1043,23 +1043,27 @@ public void writeList(List<? extends Writeable> list) throws IOException {
     }
 
     /**
-     * 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 {
-        writeVInt(list.size());
-        for (String string: list) {
-            this.writeString(string);
-        }
+    public void writeStringCollection(final Collection<String> collection) throws IOException {
+        writeCollection(collection, StreamOutput::writeString);
     }
 
     /**

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 PluginInfo(final StreamInput in) throws IOException {
         }
         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();
         }
@@ -132,7 +132,7 @@ public void writeTo(final StreamOutput out) throws IOException {
         }
         out.writeString(classname);
         if (out.getVersion().onOrAfter(Version.V_6_2_0)) {
-            out.writeStringList(extendedPlugins);
+            out.writeStringCollection(extendedPlugins);
         }
         if (out.getVersion().onOrAfter(Version.V_5_4_0)) {
             out.writeBoolean(hasNativeController);

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 InternalComposite(StreamInput in) throws IOException {
     @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

@@ -238,7 +238,7 @@ public SearchSourceBuilder(StreamInput in) throws IOException {
             }
         }
         if (in.readBoolean()) {
-            stats = in.readList(StreamInput::readString);
+            stats = in.readStringList();
         }
         suggestBuilder = in.readOptionalWriteable(SuggestBuilder::new);
         terminateAfter = in.readVInt();
@@ -303,7 +303,7 @@ public void writeTo(StreamOutput out) throws IOException {
         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.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 int hashCode() {
 
         }
 
-        final int length = randomIntBetween(0, 16);
-        final Collection<FooBar> fooBars = new ArrayList<>(length);
+        runWriteReadCollectionTest(
+                () -> 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 AutoFollowPattern(String remoteCluster,
 
         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 TimeValue getPollTimeout() {
         @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

@@ -283,7 +283,7 @@ public Request(StreamInput in) throws IOException {
             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);
@@ -302,7 +302,7 @@ public void writeTo(StreamOutput out) throws IOException {
             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

@@ -86,13 +86,13 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         @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

@@ -333,7 +333,7 @@ public void readFrom(StreamInput in) throws IOException {
             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 Request() {}
         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 Request(StreamInput in) throws IOException {
         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

@@ -203,7 +203,7 @@ public DatafeedParams(StreamInput in) throws IOException {
             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();
             }
         }
 
@@ -280,7 +280,7 @@ public void writeTo(StreamOutput out) throws IOException {
             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

@@ -254,12 +254,12 @@ public DatafeedConfig(StreamInput in) throws IOException {
         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;
         }
         if (in.readBoolean()) {
-            this.types = Collections.unmodifiableList(in.readList(StreamInput::readString));
+            this.types = Collections.unmodifiableList(in.readStringList());
         } else {
             this.types = null;
         }
@@ -423,13 +423,13 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalTimeValue(frequency);
         if (indices != null) {
             out.writeBoolean(true);
-            out.writeStringList(indices);
+            out.writeStringCollection(indices);
         } else {
             out.writeBoolean(false);
         }
         if (types != null) {
             out.writeBoolean(true);
-            out.writeStringList(types);
+            out.writeStringCollection(types);
         } else {
             out.writeBoolean(false);
         }

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

@@ -110,12 +110,12 @@ public DatafeedUpdate(StreamInput in) throws IOException {
         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;
         }
         if (in.readBoolean()) {
-            this.types = in.readList(StreamInput::readString);
+            this.types = in.readStringList();
         } else {
             this.types = null;
         }
@@ -154,13 +154,13 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalTimeValue(frequency);
         if (indices != null) {
             out.writeBoolean(true);
-            out.writeStringList(indices);
+            out.writeStringCollection(indices);
         } else {
             out.writeBoolean(false);
         }
         if (types != null) {
             out.writeBoolean(true);
-            out.writeStringList(types);
+            out.writeStringCollection(types);
         } else {
             out.writeBoolean(false);
         }