make QueryResource return ETag header if If-None-Match header is provided (#3955)

also do not process query and return HTTP 304 NOT MODIFIED if given If-None-Match value matches current ETag

server/src/main/java/io/druid/client/CachingClusteredClient.java

@@ -21,6 +21,7 @@ package io.druid.client;
 
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.common.base.Charsets;
 import com.google.common.base.Function;
 import com.google.common.base.Optional;
 import com.google.common.base.Supplier;
@@ -32,6 +33,8 @@ import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.common.collect.RangeSet;
 import com.google.common.collect.Sets;
+import com.google.common.hash.Hasher;
+import com.google.common.hash.Hashing;
 import com.google.common.util.concurrent.FutureCallback;
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListenableFuture;
@@ -64,12 +67,14 @@ import io.druid.query.SegmentDescriptor;
 import io.druid.query.aggregation.MetricManipulatorFns;
 import io.druid.query.filter.DimFilterUtils;
 import io.druid.query.spec.MultipleSpecificSegmentSpec;
+import io.druid.server.QueryResource;
 import io.druid.server.coordination.DruidServerMetadata;
 import io.druid.timeline.DataSegment;
 import io.druid.timeline.TimelineLookup;
 import io.druid.timeline.TimelineObjectHolder;
 import io.druid.timeline.partition.PartitionChunk;
 import io.druid.timeline.partition.ShardSpec;
+import org.apache.commons.codec.binary.Base64;
 import org.joda.time.Interval;
 
 import java.io.IOException;
@@ -258,6 +263,30 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
       queryCacheKey = null;
     }
 
+    if (query.getContext().get(QueryResource.HDR_IF_NONE_MATCH) != null) {
+      String prevEtag = (String) query.getContext().get(QueryResource.HDR_IF_NONE_MATCH);
+
+      //compute current Etag
+      Hasher hasher = Hashing.sha1().newHasher();
+      boolean hasOnlyHistoricalSegments = true;
+      for (Pair<ServerSelector, SegmentDescriptor> p : segments) {
+        if (!p.lhs.pick().getServer().isAssignable()) {
+          hasOnlyHistoricalSegments = false;
+          break;
+        }
+        hasher.putString(p.lhs.getSegment().getIdentifier(), Charsets.UTF_8);
+      }
+
+      if (hasOnlyHistoricalSegments) {
+        hasher.putBytes(queryCacheKey == null ? strategy.computeCacheKey(query) : queryCacheKey);
+        String currEtag = Base64.encodeBase64String(hasher.hash().asBytes());
+        responseContext.put(QueryResource.HDR_ETAG, currEtag);
+        if (prevEtag.equals(currEtag)) {
+          return Sequences.empty();
+        }
+      }
+    }
+
     if (queryCacheKey != null) {
       // cachKeys map must preserve segment ordering, in order for shards to always be combined in the same order
       Map<Pair<ServerSelector, SegmentDescriptor>, Cache.NamedKey> cacheKeys = Maps.newLinkedHashMap();

server/src/main/java/io/druid/server/QueryResource.java

@@ -87,6 +87,8 @@ public class QueryResource implements QueryCountStatsProvider
 
   protected static final int RESPONSE_CTX_HEADER_LEN_LIMIT = 7 * 1024;
 
+  public static final String HDR_IF_NONE_MATCH = "If-None-Match";
+  public static final String HDR_ETAG = "ETag";
 
   protected final QueryToolChestWarehouse warehouse;
   protected final ServerConfig config;
@@ -217,8 +219,20 @@ public class QueryResource implements QueryCountStatsProvider
         }
       }
 
+      String prevEtag = req.getHeader(HDR_IF_NONE_MATCH);
+      if (prevEtag != null) {
+        query = query.withOverriddenContext(
+            ImmutableMap.of (HDR_IF_NONE_MATCH, prevEtag)
+        );
+      }
+
       final Map<String, Object> responseContext = new MapMaker().makeMap();
       final Sequence res = query.run(texasRanger, responseContext);
+
+      if (prevEtag != null && prevEtag.equals(responseContext.get(HDR_ETAG))) {
+        return Response.notModified().build();
+      }
+
       final Sequence results;
       if (res == null) {
         results = Sequences.empty();
@@ -282,6 +296,11 @@ public class QueryResource implements QueryCountStatsProvider
             )
             .header("X-Druid-Query-Id", queryId);
 
+        if (responseContext.get(HDR_ETAG) != null) {
+          builder.header(HDR_ETAG, responseContext.get(HDR_ETAG));
+          responseContext.remove(HDR_ETAG);
+        }
+
         //Limit the response-context header, see https://github.com/druid-io/druid/issues/2331
         //Note that Response.ResponseBuilder.header(String key,Object value).build() calls value.toString()
         //and encodes the string using ASCII, so 1 char is = 1 byte

server/src/test/java/io/druid/client/CachingClusteredClientTest.java

@@ -3144,4 +3144,42 @@ public class CachingClusteredClientTest
     );
   }
 
+  @Test
+  public void testIfNoneMatch() throws Exception
+  {
+    Interval interval = new Interval("2016/2017");
+    final DataSegment dataSegment = new DataSegment(
+        "dataSource",
+        interval,
+        "ver",
+        ImmutableMap.<String, Object>of(
+            "type", "hdfs",
+            "path", "/tmp"
+        ),
+        ImmutableList.of("product"),
+        ImmutableList.of("visited_sum"),
+        NoneShardSpec.instance(),
+        9,
+        12334
+    );
+    final ServerSelector selector = new ServerSelector(
+        dataSegment,
+        new HighestPriorityTierSelectorStrategy(new RandomServerSelectorStrategy())
+    );
+    selector.addServerAndUpdateSegment(new QueryableDruidServer(servers[0], null), dataSegment);
+    timeline.add(interval, "ver", new SingleElementPartitionChunk<>(selector));
+
+    TimeBoundaryQuery query = Druids.newTimeBoundaryQueryBuilder()
+                                    .dataSource(DATA_SOURCE)
+                                    .intervals(new MultipleIntervalSegmentSpec(ImmutableList.of(interval)))
+                                    .context(ImmutableMap.<String, Object>of("If-None-Match", "aVJV29CJY93rszVW/QBy0arWZo0="))
+                                    .build();
+
+
+    Map<String, String> responseContext = new HashMap<>();
+
+    client.run(query, responseContext);
+    Assert.assertEquals("Z/eS4rQz5v477iq7Aashr6JPZa0=", responseContext.get("ETag"));
+  }
+
 }

server/src/test/java/io/druid/server/QueryResourceTest.java

@@ -127,6 +127,7 @@ public class QueryResourceTest
   public void setup()
   {
     EasyMock.expect(testServletRequest.getContentType()).andReturn(MediaType.APPLICATION_JSON).anyTimes();
+    EasyMock.expect(testServletRequest.getHeader(QueryResource.HDR_IF_NONE_MATCH)).andReturn(null).anyTimes();
     EasyMock.expect(testServletRequest.getRemoteAddr()).andReturn("localhost").anyTimes();
     queryManager = new QueryManager();
     queryResource = new QueryResource(