Factor out a class for efficient regex search over lists

RegexPathPredicate had some clever logic for avoiding matching regular
expressions over an entire search list when we can identify a common
prefix that all matching results must have. Factor this out into a new
class, RegexListSearcher, add tests, and use it from ListProjects.

Change-Id: Ie08ad8dcf09708a8aa3efcfbed6c4ee6879f80c7

gerrit-server/src/main/java/com/google/gerrit/server/project/ListProjects.java

@@ -16,6 +16,7 @@ package com.google.gerrit.server.project;
 
 import com.google.common.base.Predicate;
 import com.google.common.base.Strings;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
@@ -38,14 +39,12 @@ import com.google.gerrit.server.WebLinks;
 import com.google.gerrit.server.account.GroupCache;
 import com.google.gerrit.server.account.GroupControl;
 import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.util.RegexListSearcher;
 import com.google.gerrit.server.util.TreeFormatter;
 import com.google.gson.reflect.TypeToken;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 
-import dk.brics.automaton.RegExp;
-import dk.brics.automaton.RunAutomaton;
-
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.Ref;
@@ -462,27 +461,18 @@ public class ListProjects implements RestReadView<TopLevelResource> {
           });
     } else if (matchRegex != null) {
       checkMatchOptions(matchPrefix == null && matchSubstring == null);
-      if (matchRegex.startsWith("^")) {
+      RegexListSearcher<Project.NameKey> searcher;
-        matchRegex = matchRegex.substring(1);
-      }
-      if (matchRegex.endsWith("$") && !matchRegex.endsWith("\\$")) {
-        matchRegex = matchRegex.substring(0, matchRegex.length() - 1);
-      }
-      if (matchRegex.equals(".*")) {
-        return projectCache.all();
-      }
       try {
-        final RunAutomaton a =
+        searcher = new RegexListSearcher<Project.NameKey>(matchRegex) {
-            new RunAutomaton(new RegExp(matchRegex).toAutomaton());
+          @Override
-        return Iterables.filter(projectCache.all(),
+          public String apply(Project.NameKey in) {
-            new Predicate<Project.NameKey>() {
+            return in.get();
-              public boolean apply(Project.NameKey in) {
-                return a.run(in.get());
           }
-            });
+        };
       } catch (IllegalArgumentException e) {
         throw new BadRequestException(e.getMessage());
       }
+      return searcher.search(ImmutableList.copyOf(projectCache.all()));
     } else {
       return projectCache.all();
     }

gerrit-server/src/main/java/com/google/gerrit/server/query/change/RegexPathPredicate.java

@@ -16,76 +16,21 @@ package com.google.gerrit.server.query.change;
 
 import com.google.gerrit.server.index.ChangeField;
 import com.google.gerrit.server.index.RegexPredicate;
+import com.google.gerrit.server.util.RegexListSearcher;
 import com.google.gwtorm.server.OrmException;
 
-import dk.brics.automaton.Automaton;
-import dk.brics.automaton.RegExp;
-import dk.brics.automaton.RunAutomaton;
-
-import java.util.Collections;
 import java.util.List;
 
 class RegexPathPredicate extends RegexPredicate<ChangeData> {
-  private final RunAutomaton pattern;
-
-  private final String prefixBegin;
-  private final String prefixEnd;
-  private final int prefixLen;
-  private final boolean prefixOnly;
-
   RegexPathPredicate(String fieldName, String re) {
     super(ChangeField.PATH, re);
-
-    if (re.startsWith("^")) {
-      re = re.substring(1);
-    }
-
-    if (re.endsWith("$") && !re.endsWith("\\$")) {
-      re = re.substring(0, re.length() - 1);
-    }
-
-    Automaton automaton = new RegExp(re).toAutomaton();
-    prefixBegin = automaton.getCommonPrefix();
-    prefixLen = prefixBegin.length();
-
-    if (0 < prefixLen) {
-      char max = (char) (prefixBegin.charAt(prefixLen - 1) + 1);
-      prefixEnd = prefixBegin.substring(0, prefixLen - 1) + max;
-      prefixOnly = re.equals(prefixBegin + ".*");
-    } else {
-      prefixEnd = "";
-      prefixOnly = false;
-    }
-
-    pattern = prefixOnly ? null : new RunAutomaton(automaton);
   }
 
   @Override
   public boolean match(ChangeData object) throws OrmException {
     List<String> files = object.currentFilePaths();
     if (files != null) {
-      int begin, end;
+      return RegexListSearcher.ofStrings(getValue()).hasMatch(files);
-
-      if (0 < prefixLen) {
-        begin = find(files, prefixBegin);
-        end = find(files, prefixEnd);
-      } else {
-        begin = 0;
-        end = files.size();
-      }
-
-      if (prefixOnly) {
-        return begin < end;
-      }
-
-      while (begin < end) {
-        if (pattern.run(files.get(begin++))) {
-          return true;
-        }
-      }
-
-      return false;
-
     } else {
       // The ChangeData can't do expensive lookups right now. Bypass
       // them and include the result anyway. We might be able to do
@@ -95,11 +40,6 @@ class RegexPathPredicate extends RegexPredicate<ChangeData> {
     }
   }
 
-  private static int find(List<String> files, String p) {
-    int r = Collections.binarySearch(files, p);
-    return r < 0 ? -(r + 1) : r;
-  }
-
   @Override
   public int getCost() {
     return 1;

gerrit-server/src/main/java/com/google/gerrit/server/util/RegexListSearcher.java

@@ -0,0 +1,112 @@
+// Copyright (C) 2014 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.util;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.common.base.Function;
+import com.google.common.base.Predicate;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Iterables;
+import com.google.common.collect.Lists;
+import com.google.common.primitives.Chars;
+
+import dk.brics.automaton.Automaton;
+import dk.brics.automaton.RegExp;
+import dk.brics.automaton.RunAutomaton;
+
+import java.util.Collections;
+import java.util.List;
+
+/** Helper to search sorted lists for elements matching a regex. */
+public abstract class RegexListSearcher<T> implements Function<T, String> {
+  public static RegexListSearcher<String> ofStrings(String re) {
+    return new RegexListSearcher<String>(re) {
+      @Override
+      public String apply(String in) {
+        return in;
+      }
+    };
+  }
+
+  private final RunAutomaton pattern;
+
+  private final String prefixBegin;
+  private final String prefixEnd;
+  private final int prefixLen;
+  private final boolean prefixOnly;
+
+  public RegexListSearcher(String re) {
+    if (re.startsWith("^")) {
+      re = re.substring(1);
+    }
+
+    if (re.endsWith("$") && !re.endsWith("\\$")) {
+      re = re.substring(0, re.length() - 1);
+    }
+
+    Automaton automaton = new RegExp(re).toAutomaton();
+    prefixBegin = automaton.getCommonPrefix();
+    prefixLen = prefixBegin.length();
+
+    if (0 < prefixLen) {
+      char max = Chars.checkedCast(prefixBegin.charAt(prefixLen - 1) + 1);
+      prefixEnd = prefixBegin.substring(0, prefixLen - 1) + max;
+      prefixOnly = re.equals(prefixBegin + ".*");
+    } else {
+      prefixEnd = "";
+      prefixOnly = false;
+    }
+
+    pattern = prefixOnly ? null : new RunAutomaton(automaton);
+  }
+
+  public Iterable<T> search(List<T> list) {
+    checkNotNull(list);
+    int begin, end;
+
+    if (0 < prefixLen) {
+      // Assumes many consecutive elements may have the same prefix, so the cost
+      // of two binary searches is less than iterating to find the endpoints.
+      begin = find(list, prefixBegin);
+      end = find(list, prefixEnd);
+    } else {
+      begin = 0;
+      end = list.size();
+    }
+
+    if (prefixOnly) {
+      return begin < end ? list.subList(begin, end) : ImmutableList.<T> of();
+    }
+
+    return Iterables.filter(
+        list.subList(begin, end),
+        new Predicate<T>() {
+          @Override
+          public boolean apply(T in) {
+            return pattern.run(RegexListSearcher.this.apply(in));
+          }
+        });
+  }
+
+  public boolean hasMatch(List<T> list) {
+    return !Iterables.isEmpty(search(list));
+  }
+
+  private int find(List<T> list, String p) {
+    int r = Collections.binarySearch(Lists.transform(list, this), p);
+    return r < 0 ? -(r + 1) : r;
+  }
+}

gerrit-server/src/test/java/com/google/gerrit/server/util/RegexListSearcherTest.java

@@ -0,0 +1,84 @@
+// Copyright (C) 2014 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Ordering;
+
+import org.junit.Test;
+
+import java.util.List;
+
+public class RegexListSearcherTest {
+  private static final List<String> EMPTY = ImmutableList.of();
+
+  @Test
+  public void emptyList() {
+    assertSearchReturns(EMPTY, "pat", EMPTY);
+  }
+
+  @Test
+  public void hasMatch() {
+    List<String> list = ImmutableList.of("bar", "foo", "quux");
+    assertTrue(RegexListSearcher.ofStrings("foo").hasMatch(list));
+    assertFalse(RegexListSearcher.ofStrings("xyz").hasMatch(list));
+  }
+
+  @Test
+  public void anchors() {
+    List<String> list = ImmutableList.of("foo");
+    assertSearchReturns(list, "^f.*", list);
+    assertSearchReturns(list, "^f.*o$", list);
+    assertSearchReturns(list, "f.*o$", list);
+    assertSearchReturns(list, "f.*o$", list);
+    assertSearchReturns(EMPTY, "^.*\\$", list);
+  }
+
+  @Test
+  public void noCommonPrefix() {
+    List<String> list = ImmutableList.of("bar", "foo", "quux");
+    assertSearchReturns(ImmutableList.of("foo"), "f.*", list);
+    assertSearchReturns(ImmutableList.of("foo"), ".*o.*", list);
+    assertSearchReturns(ImmutableList.of("bar", "foo", "quux"), ".*[aou].*",
+        list);
+  }
+
+  @Test
+  public void commonPrefix() {
+    List<String> list = ImmutableList.of(
+        "bar",
+        "baz",
+        "foo1",
+        "foo2",
+        "foo3",
+        "quux");
+    assertSearchReturns(ImmutableList.of("bar", "baz"), "b.*", list);
+    assertSearchReturns(ImmutableList.of("foo1", "foo2"), "foo[12]", list);
+    assertSearchReturns(ImmutableList.of("foo1", "foo2", "foo3"), "foo.*",
+        list);
+    assertSearchReturns(ImmutableList.of("quux"), "q.*", list);
+  }
+
+  private void assertSearchReturns(List<?> expected, String re,
+    List<String> inputs) {
+    assertTrue(Ordering.natural().isOrdered(inputs));
+    assertEquals(expected,
+        ImmutableList.copyOf(RegexListSearcher.ofStrings(re).search(inputs)));
+  }
+}