Optimize StringMatcher for match-all patterns (#77738)

Detect a StringMatcher of "*" and optimize it as a predicate of

    s -> true

This is about 80% faster than using an automaton.
This speed improvement is very minor on a single execution but can
add up to milliseconds is used in a tight loop - e.g. testing
against every indices in a large cluster

Author: tvernum

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/support/StringMatcher.java

@@ -36,6 +36,8 @@ public class StringMatcher implements Predicate<String> {
 
     private static final StringMatcher MATCH_NOTHING = new StringMatcher("(empty)", s -> false);
 
+    protected static final Predicate<String> ALWAYS_TRUE_PREDICATE = s -> true;
+
     private final String description;
     private final Predicate<String> predicate;
     private static final Logger LOGGER = LogManager.getLogger(StringMatcher.class);
@@ -67,6 +69,11 @@ public boolean test(String s) {
         return predicate.test(s);
     }
 
+    // For testing
+    Predicate<String> getPredicate() {
+        return predicate;
+    }
+
     @Override
     public StringMatcher or(Predicate<? super String> other) {
         Objects.requireNonNull(other);
@@ -118,6 +125,9 @@ public StringMatcher build() {
             }
 
             final String description = describe(allText);
+            if (nonExactMatch.contains("*")) {
+                return new StringMatcher(description, ALWAYS_TRUE_PREDICATE);
+            }
             if (exactMatch.isEmpty()) {
                 return new StringMatcher(description, buildAutomataPredicate(nonExactMatch));
             }

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/support/StringMatcherTests.java

@@ -11,8 +11,12 @@
 
 import java.util.List;
 import java.util.Locale;
+import java.util.function.Supplier;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.sameInstance;
 
 public class StringMatcherTests extends ESTestCase {
 
@@ -23,6 +27,31 @@ public void testEmptySet() throws Exception {
         }
     }
 
+    public void testMatchAllWildcard() throws Exception {
+        Supplier<String> randomPattern = () -> {
+            final String s = randomAlphaOfLengthBetween(3, 5);
+            switch (randomIntBetween(1, 4)) {
+                case 1:
+                    return s;
+                case 2:
+                    return s + "*";
+                case 3:
+                    return "*" + s;
+                default:
+                    return "*" + s + "*";
+            }
+        };
+        final List<String> patterns = Stream.of(randomList(0, 3, randomPattern), List.of("*"), randomList(0, 3, randomPattern))
+            .flatMap(List::stream)
+            .collect(Collectors.toList());
+        final StringMatcher matcher = StringMatcher.of(patterns);
+        for (int i = 0; i < 10; i++) {
+            assertMatch(matcher, randomAlphaOfLengthBetween(i, 20));
+        }
+
+        assertThat(matcher.getPredicate(), sameInstance(StringMatcher.ALWAYS_TRUE_PREDICATE));
+    }
+
     public void testSingleWildcard() throws Exception {
         final String prefix = randomAlphaOfLengthBetween(3, 5);
         final StringMatcher matcher = StringMatcher.of(prefix + "*");