Add pluggable XContentBuilder writers and human readable writers (#29120)

* Add pluggable XContentBuilder writers and human readable writers

This adds the ability to use SPI to plug in writers for XContentBuilder. By
implementing the XContentBuilderProvider class we can allow Elasticsearch to
plug in different ways to encode types to JSON.

Important caveat for this, we should always try to have the class implement
`ToXContentFragment` first, however, in the case of classes from our
dependencies (think Joda classes or Lucene classes) we need a way to specify
writers for these classes.

This also makes the human-readable field writers generic and pluggable, so that
we no longer need to tie XContentBuilder to things like `TimeValue` and
`ByteSizeValue`. Contained as part of this moves all the TimeValue human
readable fields to the new `humanReadableField` method. A future commit will
move the `ByteSizeValue` calls over to this method.

Relates to #28504

Author: dakrone

server/src/main/java/org/elasticsearch/action/admin/cluster/health/ClusterHealthResponse.java

@@ -245,7 +245,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         builder.field(DELAYED_UNASSIGNED_SHARDS, getDelayedUnassignedShards());
         builder.field(NUMBER_OF_PENDING_TASKS, getNumberOfPendingTasks());
         builder.field(NUMBER_OF_IN_FLIGHT_FETCH, getNumberOfInFlightFetch());
-        builder.timeValueField(TASK_MAX_WAIT_TIME_IN_QUEUE_IN_MILLIS, TASK_MAX_WAIT_TIME_IN_QUEUE, getTaskMaxWaitingTime());
+        builder.humanReadableField(TASK_MAX_WAIT_TIME_IN_QUEUE_IN_MILLIS, TASK_MAX_WAIT_TIME_IN_QUEUE, getTaskMaxWaitingTime());
         builder.percentageField(ACTIVE_SHARDS_PERCENT_AS_NUMBER, ACTIVE_SHARDS_PERCENT, getActiveShardsPercent());
 
         String level = params.param("level", "cluster");

server/src/main/java/org/elasticsearch/action/admin/cluster/node/info/NodesInfoResponse.java

@@ -68,7 +68,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
             builder.field("version", nodeInfo.getVersion());
             builder.field("build_hash", nodeInfo.getBuild().shortHash());
             if (nodeInfo.getTotalIndexingBuffer() != null) {
-                builder.byteSizeField("total_indexing_buffer", "total_indexing_buffer_in_bytes", nodeInfo.getTotalIndexingBuffer());
+                builder.humanReadableField("total_indexing_buffer", "total_indexing_buffer_in_bytes", nodeInfo.getTotalIndexingBuffer());
             }
 
             builder.startArray("roles");

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/status/SnapshotStats.java

@@ -22,6 +22,7 @@
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Streamable;
+import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.ToXContentFragment;
 import org.elasticsearch.common.xcontent.XContentBuilder;
@@ -143,7 +144,7 @@ public XContentBuilder toXContent(XContentBuilder builder, ToXContent.Params par
         builder.byteSizeField(Fields.TOTAL_SIZE_IN_BYTES, Fields.TOTAL_SIZE, getTotalSize());
         builder.byteSizeField(Fields.PROCESSED_SIZE_IN_BYTES, Fields.PROCESSED_SIZE, getProcessedSize());
         builder.field(Fields.START_TIME_IN_MILLIS, getStartTime());
-        builder.timeValueField(Fields.TIME_IN_MILLIS, Fields.TIME, getTime());
+        builder.humanReadableField(Fields.TIME_IN_MILLIS, Fields.TIME, new TimeValue(getTime()));
         builder.endObject();
         return builder;
     }

server/src/main/java/org/elasticsearch/action/admin/cluster/stats/ClusterStatsNodes.java

@@ -488,7 +488,7 @@ static final class Fields {
         @Override
         public XContentBuilder toXContent(XContentBuilder builder, Params params)
                 throws IOException {
-            builder.timeValueField(Fields.MAX_UPTIME_IN_MILLIS, Fields.MAX_UPTIME, maxUptime);
+            builder.humanReadableField(Fields.MAX_UPTIME_IN_MILLIS, Fields.MAX_UPTIME, new TimeValue(maxUptime));
             builder.startArray(Fields.VERSIONS);
             for (ObjectIntCursor<JvmVersion> v : versions) {
                 builder.startObject();

server/src/main/java/org/elasticsearch/action/admin/indices/segments/IndicesSegmentResponse.java

@@ -198,7 +198,7 @@ static void toXContent(XContentBuilder builder, Sort sort) throws IOException {
     static void toXContent(XContentBuilder builder, Accountable tree) throws IOException {
         builder.startObject();
         builder.field(Fields.DESCRIPTION, tree.toString());
-        builder.byteSizeField(Fields.SIZE_IN_BYTES, Fields.SIZE, new ByteSizeValue(tree.ramBytesUsed()));
+        builder.humanReadableField(Fields.SIZE_IN_BYTES, Fields.SIZE, new ByteSizeValue(tree.ramBytesUsed()));
         Collection<Accountable> children = tree.getChildResources();
         if (children.isEmpty() == false) {
             builder.startArray(Fields.CHILDREN);

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

@@ -24,6 +24,7 @@
 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.unit.TimeValue;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.snapshots.Snapshot;
 
@@ -145,7 +146,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
             {
                 builder.field("repository", entry.snapshot.getRepository());
                 builder.field("snapshot", entry.snapshot.getSnapshotId().getName());
-                builder.timeValueField("start_time_millis", "start_time", entry.startTime);
+                builder.humanReadableField("start_time_millis", "start_time", new TimeValue(entry.startTime));
                 builder.field("repository_state_id", entry.repositoryStateId);
             }
             builder.endObject();

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

@@ -27,6 +27,7 @@
 import org.elasticsearch.common.collect.ImmutableOpenMap;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.index.shard.ShardId;
@@ -514,7 +515,7 @@ public void toXContent(Entry entry, XContentBuilder builder, ToXContent.Params p
             }
         }
         builder.endArray();
-        builder.timeValueField(START_TIME_MILLIS, START_TIME, entry.startTime());
+        builder.humanReadableField(START_TIME_MILLIS, START_TIME, new TimeValue(entry.startTime()));
         builder.field(REPOSITORY_STATE_ID, entry.getRepositoryStateId());
         builder.startArray(SHARDS);
         {

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

@@ -289,8 +289,10 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
             builder.field("allocation_id", allocationId);
         }
         if (allocationStatus == AllocationStatus.DELAYED_ALLOCATION) {
-            builder.timeValueField("configured_delay_in_millis", "configured_delay", TimeValue.timeValueMillis(configuredDelayInMillis));
-            builder.timeValueField("remaining_delay_in_millis", "remaining_delay", TimeValue.timeValueMillis(remainingDelayInMillis));
+            builder.humanReadableField("configured_delay_in_millis", "configured_delay",
+                TimeValue.timeValueMillis(configuredDelayInMillis));
+            builder.humanReadableField("remaining_delay_in_millis", "remaining_delay",
+                TimeValue.timeValueMillis(remainingDelayInMillis));
         }
         nodeDecisionsToXContent(nodeDecisions, builder, params);
         return builder;

server/src/main/java/org/elasticsearch/common/xcontent/XContentBuilder.java

@@ -43,8 +43,8 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
+import java.util.ServiceLoader;
 import java.util.Set;
-import java.util.concurrent.TimeUnit;
 
 /**
  * A utility to build XContent (ie json).
@@ -85,6 +85,7 @@ public static XContentBuilder builder(XContent xContent, Set<String> includes, S
     public static final DateTimeFormatter DEFAULT_DATE_PRINTER = ISODateTimeFormat.dateTime().withZone(DateTimeZone.UTC);
 
     private static final Map<Class<?>, Writer> WRITERS;
+    private static final Map<Class<?>, HumanReadableTransformer> HUMAN_READABLE_TRANSFORMERS;
     static {
         Map<Class<?>, Writer> writers = new HashMap<>();
         writers.put(Boolean.class, (b, v) -> b.value((Boolean) v));
@@ -105,14 +106,43 @@ public static XContentBuilder builder(XContent xContent, Set<String> includes, S
         writers.put(String.class, (b, v) -> b.value((String) v));
         writers.put(String[].class, (b, v) -> b.values((String[]) v));
 
+
+        Map<Class<?>, HumanReadableTransformer> humanReadableTransformer = new HashMap<>();
+        // These will be moved to a different class at a later time to decouple them from XContentBuilder
+        humanReadableTransformer.put(TimeValue.class, v -> ((TimeValue) v).millis());
+        humanReadableTransformer.put(ByteSizeValue.class, v -> ((ByteSizeValue) v).getBytes());
+
+        // Load pluggable extensions
+        for (XContentBuilderExtension service : ServiceLoader.load(XContentBuilderExtension.class)) {
+            Map<Class<?>, Writer> addlWriters = service.getXContentWriters();
+            Map<Class<?>, HumanReadableTransformer> addlTransformers = service.getXContentHumanReadableTransformers();
+
+            addlWriters.forEach((key, value) -> Objects.requireNonNull(value,
+                "invalid null xcontent writer for class " + key));
+            addlTransformers.forEach((key, value) -> Objects.requireNonNull(value,
+                "invalid null xcontent transformer for human readable class " + key));
+
+            writers.putAll(addlWriters);
+            humanReadableTransformer.putAll(addlTransformers);
+        }
+
         WRITERS = Collections.unmodifiableMap(writers);
+        HUMAN_READABLE_TRANSFORMERS = Collections.unmodifiableMap(humanReadableTransformer);
     }
 
     @FunctionalInterface
-    private interface Writer {
+    public interface Writer {
         void write(XContentBuilder builder, Object value) throws IOException;
     }
 
+    /**
+     * Interface for transforming complex objects into their "raw" equivalents for human-readable fields
+     */
+    @FunctionalInterface
+    public interface HumanReadableTransformer {
+        Object rawValue(Object value) throws IOException;
+    }
+
     /**
      * XContentGenerator used to build the XContent object
      */
@@ -856,33 +886,30 @@ private XContentBuilder value(Iterable<?> values, boolean ensureNoSelfReferences
     }
 
     ////////////////////////////////////////////////////////////////////////////
-    // Misc.
+    // Human readable fields
+    //
+    // These are fields that have a "raw" value and a "human readable" value,
+    // such as time values or byte sizes. The human readable variant is only
+    // used if the humanReadable flag has been set
     //////////////////////////////////
 
-    public XContentBuilder timeValueField(String rawFieldName, String readableFieldName, TimeValue timeValue) throws IOException {
+    public XContentBuilder humanReadableField(String rawFieldName, String readableFieldName, Object value) throws IOException {
         if (humanReadable) {
-            field(readableFieldName, timeValue.toString());
+            field(readableFieldName, Objects.toString(value));
         }
-        field(rawFieldName, timeValue.millis());
-        return this;
-    }
-
-    public XContentBuilder timeValueField(String rawFieldName, String readableFieldName, long rawTime) throws IOException {
-        if (humanReadable) {
-            field(readableFieldName, new TimeValue(rawTime).toString());
+        HumanReadableTransformer transformer = HUMAN_READABLE_TRANSFORMERS.get(value.getClass());
+        if (transformer != null) {
+            Object rawValue = transformer.rawValue(value);
+            field(rawFieldName, rawValue);
+        } else {
+            throw new IllegalArgumentException("no raw transformer found for class " + value.getClass());
         }
-        field(rawFieldName, rawTime);
         return this;
     }
 
-    public XContentBuilder timeValueField(String rawFieldName, String readableFieldName, long rawTime, TimeUnit timeUnit) throws
-            IOException {
-        if (humanReadable) {
-            field(readableFieldName, new TimeValue(rawTime, timeUnit).toString());
-        }
-        field(rawFieldName, rawTime);
-        return this;
-    }
+    ////////////////////////////////////////////////////////////////////////////
+    // Misc.
+    //////////////////////////////////
 
 
     public XContentBuilder percentageField(String rawFieldName, String readableFieldName, double percentage) throws IOException {
@@ -893,14 +920,6 @@ public XContentBuilder percentageField(String rawFieldName, String readableField
         return this;
     }
 
-    public XContentBuilder byteSizeField(String rawFieldName, String readableFieldName, ByteSizeValue byteSizeValue) throws IOException {
-        if (humanReadable) {
-            field(readableFieldName, byteSizeValue.toString());
-        }
-        field(rawFieldName, byteSizeValue.getBytes());
-        return this;
-    }
-
     public XContentBuilder byteSizeField(String rawFieldName, String readableFieldName, long rawSize) throws IOException {
         if (humanReadable) {
             field(readableFieldName, new ByteSizeValue(rawSize).toString());

server/src/main/java/org/elasticsearch/common/xcontent/XContentBuilderExtension.java

@@ -0,0 +1,64 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.common.xcontent;
+
+import java.util.Map;
+
+/**
+ * This interface provides a way for non-JDK classes to plug in a way to serialize to xcontent.
+ *
+ * It is <b>greatly</b> preferred that you implement {@link ToXContentFragment}
+ * in the class for encoding, however, in some situations you may not own the
+ * class, in which case you can add an implementation here for encoding it.
+ */
+public interface XContentBuilderExtension {
+
+    /**
+     * Used for plugging in a generic writer for a class, for example, an example implementation:
+     *
+     * <pre>
+     * {@code
+     *     Map<Class<?>, XContentBuilder.Writer> addlWriters = new HashMap<>();
+     *     addlWriters.put(BytesRef.class, (builder, value) -> b.value(((BytesRef) value).utf8String()));
+     *     return addlWriters;
+     * }
+     * </pre>
+     *
+     * @return a map of class name to writer
+     */
+    Map<Class<?>, XContentBuilder.Writer> getXContentWriters();
+
+    /**
+     * Used for plugging in a human readable version of a class's encoding. It is assumed that
+     * the human readable equivalent is <b>always</b> behind the {@code toString()} method, so
+     * this transformer returns the raw value to be used.
+     *
+     * An example implementation:
+     *
+     * <pre>
+     * {@code
+     *     Map<Class<?>, XContentBuilder.HumanReadableTransformer> transformers = new HashMap<>();
+     *     transformers.put(ByteSizeValue.class, (value) -> ((ByteSizeValue) value).bytes());
+     * }
+     * </pre>
+     * @return a map of class name to transformer used to retrieve raw value
+     */
+    Map<Class<?>, XContentBuilder.HumanReadableTransformer> getXContentHumanReadableTransformers();
+}