[Tests] Fix alias names in PutIndexTemplateRequestTests (#30960)

The randomized alias names could contain unicode controll charactes that don't
survive an xContent rendering and parsing roundtrip when using the YAML xContent
type. This fix filters the randomized unicode string for control characters to
avoid this particular problem.

Closes #30911

Author: Christoph Büscher

server/src/main/java/org/elasticsearch/action/admin/indices/alias/Alias.java

@@ -28,7 +28,8 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Streamable;
 import org.elasticsearch.common.xcontent.ToXContent;
-import org.elasticsearch.common.xcontent.ToXContentObject;
+import org.elasticsearch.common.xcontent.ToXContent.Params;
+import org.elasticsearch.common.xcontent.ToXContentFragment;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentParser;
@@ -42,7 +43,7 @@
 /**
  * Represents an alias, to be associated with an index
  */
-public class Alias implements Streamable, ToXContentObject {
+public class Alias implements Streamable, ToXContentFragment {
 
     private static final ParseField FILTER = new ParseField("filter");
     private static final ParseField ROUTING = new ParseField("routing");
@@ -248,6 +249,11 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         return builder;
     }
 
+    @Override
+    public String toString() {
+        return Strings.toString(this);
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

server/src/test/java/org/elasticsearch/action/admin/indices/template/put/PutIndexTemplateRequestTests.java

@@ -150,7 +150,9 @@ protected PutIndexTemplateRequest createTestInstance() {
         request.patterns(Arrays.asList(generateRandomStringArray(20, 100, false, false)));
         int numAlias = between(0, 5);
         for (int i = 0; i < numAlias; i++) {
-            Alias alias = new Alias(randomRealisticUnicodeOfLengthBetween(1, 10));
+            // some ASCII or Latin-1 control characters, especially newline, can lead to
+            // problems with yaml parsers, that's why we filter them here (see #30911)
+            Alias alias = new Alias(randomRealisticUnicodeOfLengthBetween(1, 10).replaceAll("\\p{Cc}", ""));
             if (randomBoolean()) {
                 alias.indexRouting(randomRealisticUnicodeOfLengthBetween(1, 10));
             }