From 056c698540b1bb51eb09f28b4e51e7be7e98dbbc Mon Sep 17 00:00:00 2001
From: Vishnu Chilamakuru <vishnu.chilamakuru@gmail.com>
Date: Mon, 9 Dec 2019 19:09:05 +0530
Subject: [PATCH] Add Validation for maxQueryTerms to be greater than 0 for
 MoreLikeThisQuery (#49966)

Adds validation for maxQueryTerms to be greater than 0 for MoreLikeThisQuery
and MoreLikeThisQueryBuilder.

Closes #49927
---
 .../common/lucene/search/MoreLikeThisQuery.java      |  3 +++
 .../index/query/MoreLikeThisQueryBuilder.java        |  3 +++
 .../search/morelikethis/MoreLikeThisQueryTests.java  | 12 ++++++++++++
 .../index/query/MoreLikeThisQueryBuilderTests.java   | 12 +++++++++++-
 4 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/server/src/main/java/org/elasticsearch/common/lucene/search/MoreLikeThisQuery.java b/server/src/main/java/org/elasticsearch/common/lucene/search/MoreLikeThisQuery.java
index 394b8bbe65d..23764a18a3e 100644
--- a/server/src/main/java/org/elasticsearch/common/lucene/search/MoreLikeThisQuery.java
+++ b/server/src/main/java/org/elasticsearch/common/lucene/search/MoreLikeThisQuery.java
@@ -308,6 +308,9 @@ public class MoreLikeThisQuery extends Query {
     }
 
     public void setMaxQueryTerms(int maxQueryTerms) {
+        if (maxQueryTerms <= 0) {
+            throw new IllegalArgumentException("requires 'maxQueryTerms' to be greater than 0");
+        }
         this.maxQueryTerms = maxQueryTerms;
     }
 
diff --git a/server/src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilder.java b/server/src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilder.java
index 120036f5484..4c7823c8029 100644
--- a/server/src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilder.java
+++ b/server/src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilder.java
@@ -641,6 +641,9 @@ public class MoreLikeThisQueryBuilder extends AbstractQueryBuilder<MoreLikeThisQ
      * Defaults to {@code 25}.
      */
     public MoreLikeThisQueryBuilder maxQueryTerms(int maxQueryTerms) {
+        if (maxQueryTerms <= 0) {
+            throw new IllegalArgumentException("requires 'maxQueryTerms' to be greater than 0");
+        }
         this.maxQueryTerms = maxQueryTerms;
         return this;
     }
diff --git a/server/src/test/java/org/elasticsearch/common/lucene/search/morelikethis/MoreLikeThisQueryTests.java b/server/src/test/java/org/elasticsearch/common/lucene/search/morelikethis/MoreLikeThisQueryTests.java
index fb09ceb839c..337c61243ba 100644
--- a/server/src/test/java/org/elasticsearch/common/lucene/search/morelikethis/MoreLikeThisQueryTests.java
+++ b/server/src/test/java/org/elasticsearch/common/lucene/search/morelikethis/MoreLikeThisQueryTests.java
@@ -33,6 +33,7 @@ import org.elasticsearch.common.lucene.Lucene;
 import org.elasticsearch.common.lucene.search.MoreLikeThisQuery;
 import org.elasticsearch.test.ESTestCase;
 
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 
 public class MoreLikeThisQueryTests extends ESTestCase {
@@ -64,4 +65,15 @@ public class MoreLikeThisQueryTests extends ESTestCase {
         reader.close();
         indexWriter.close();
     }
+
+    public void testValidateMaxQueryTerms() {
+        IllegalArgumentException e1 = expectThrows(IllegalArgumentException.class,
+            () ->  new MoreLikeThisQuery("lucene", new String[]{"text"}, Lucene.STANDARD_ANALYZER).setMaxQueryTerms(0));
+        assertThat(e1.getMessage(), containsString("requires 'maxQueryTerms' to be greater than 0"));
+
+        IllegalArgumentException e2 = expectThrows(IllegalArgumentException.class,
+            () -> new MoreLikeThisQuery("lucene", new String[]{"text"}, Lucene.STANDARD_ANALYZER).setMaxQueryTerms(-3));
+        assertThat(e2.getMessage(), containsString("requires 'maxQueryTerms' to be greater than 0"));
+    }
+
 }
diff --git a/server/src/test/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilderTests.java b/server/src/test/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilderTests.java
index 9b588eb2f16..c17422e3f31 100644
--- a/server/src/test/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilderTests.java
+++ b/server/src/test/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilderTests.java
@@ -174,7 +174,7 @@ public class MoreLikeThisQueryBuilderTests extends AbstractQueryTestCase<MoreLik
             queryBuilder.unlike(randomUnlikeItems);
         }
         if (randomBoolean()) {
-            queryBuilder.maxQueryTerms(randomInt(25));
+            queryBuilder.maxQueryTerms(randomIntBetween(1, 25));
         }
         if (randomBoolean()) {
             queryBuilder.minTermFreq(randomInt(5));
@@ -351,6 +351,16 @@ public class MoreLikeThisQueryBuilderTests extends AbstractQueryTestCase<MoreLik
         assertThat(mltQuery.getMaxQueryTerms(), equalTo(12));
     }
 
+    public void testValidateMaxQueryTerms() {
+        IllegalArgumentException e1 = expectThrows(IllegalArgumentException.class,
+            () -> new MoreLikeThisQueryBuilder(new String[]{"name.first", "name.last"}, new String[]{"something"}, null).maxQueryTerms(0));
+        assertThat(e1.getMessage(), containsString("requires 'maxQueryTerms' to be greater than 0"));
+
+        IllegalArgumentException e2 = expectThrows(IllegalArgumentException.class,
+            () -> new MoreLikeThisQueryBuilder(new String[]{"name.first", "name.last"}, new String[]{"something"}, null).maxQueryTerms(-3));
+        assertThat(e2.getMessage(), containsString("requires 'maxQueryTerms' to be greater than 0"));
+    }
+
     public void testItemSerialization() throws IOException {
         Item expectedItem = generateRandomItem();
         BytesStreamOutput output = new BytesStreamOutput();