Reject scroll query if size is 0 (#22552)

core/src/main/java/org/elasticsearch/action/search/SearchRequest.java

@@ -161,17 +161,21 @@ public void writeTo(StreamOutput out) throws IOException {
     @Override
     public ActionRequestValidationException validate() {
         ActionRequestValidationException validationException = null;
-        if (source != null && source.trackTotalHits() == false && scroll() != null) {
+        final Scroll scroll = scroll();
+        if (source != null && source.trackTotalHits() == false && scroll != null) {
             validationException =
                 addValidationError("disabling [track_total_hits] is not allowed in a scroll context", validationException);
         }
-        if (source != null && source.from() > 0 &&  scroll() != null) {
+        if (source != null && source.from() > 0 && scroll != null) {
             validationException =
                 addValidationError("using [from] is not allowed in a scroll context", validationException);
         }
-        if (requestCache != null && requestCache && scroll() != null) {
+        if (requestCache != null && requestCache && scroll != null) {
             validationException =
-                addValidationError("[request_cache] cannot be used in a a scroll context", validationException);
+                addValidationError("[request_cache] cannot be used in a scroll context", validationException);
+        }
+        if (source != null && source.size() == 0 && scroll != null) {
+            validationException = addValidationError("[size] cannot be [0] in a scroll context", validationException);
         }
         return validationException;
     }

core/src/test/java/org/elasticsearch/search/SearchRequestTests.java

@@ -82,7 +82,6 @@ public void testIllegalArguments() {
     }
 
     public void testValidate() throws IOException {
-
         {
             // if scroll isn't set, validate should never add errors
             SearchRequest searchRequest = createSearchRequest().source(new SearchSourceBuilder());
@@ -114,6 +113,16 @@ public void testValidate() throws IOException {
             assertEquals(1, validationErrors.validationErrors().size());
             assertEquals("using [from] is not allowed in a scroll context", validationErrors.validationErrors().get(0));
         }
+        {
+            // scroll and `size` is `0`
+            SearchRequest searchRequest = createSearchRequest().source(new SearchSourceBuilder().size(0));
+            searchRequest.requestCache(false);
+            searchRequest.scroll(new TimeValue(1000));
+            ActionRequestValidationException validationErrors = searchRequest.validate();
+            assertNotNull(validationErrors);
+            assertEquals(1, validationErrors.validationErrors().size());
+            assertEquals("[size] cannot be [0] in a scroll context", validationErrors.validationErrors().get(0));
+        }
     }
 
     public void testEqualsAndHashcode() throws IOException {

rest-api-spec/src/main/resources/rest-api-spec/test/scroll/10_basic.yml

@@ -206,11 +206,30 @@
       indices.create:
         index: test_scroll
   - do:
-      catch: /\[request_cache\] cannot be used in a a scroll context/
+      catch: /\[request_cache\] cannot be used in a scroll context/
       search:
         index: test_scroll
         scroll: 1m
         request_cache: true
         body:
           query:
             match_all: {}
+
+---
+"Scroll with size 0":
+  - skip:
+      version: " - 6.99.99"
+      reason:  the error message has been added in v7.0.0
+  - do:
+      indices.create:
+        index: test_scroll
+  - do:
+      catch: /\[size\] cannot be \[0\] in a scroll context/
+      search:
+        index: test_scroll
+        scroll: 1m
+        request_cache: true
+        body:
+          query:
+            match_all: {}
+          size: 0