Fix FastWildcardGroup bug. We insert all-wildcard patterns in *reverse* order,

and should match them forwards as a result.  Add a couple of tests beyond
Steve's initial repro.

#1294

Author: Jan-Willem Maessen

pagespeed/kernel/base/fast_wildcard_group.cc

@@ -33,10 +33,6 @@
 namespace net_instaweb {
 
 namespace {
-// Don't generate a hash unless there are this many
-// non-wildcard-only patterns.
-const int kMinPatterns = 11;
-
 // Maximum rolling hash window size
 const int32 kMaxRollingHashWindow = 256;
 
@@ -266,23 +262,24 @@ bool FastWildcardGroup::Match(const StringPiece& str, bool allow) const {
     return allow;
   }
   int max_effective_index = kNoEntry;
-  // Start by matching against all-wildcard patterns in reverse order,
-  // stopping if a match is found (since earlier matches will have
-  // a smaller index and be overridden by the already-found match).
-  // TODO(jmaessen): These patterns all devolve to
-  // a string length check (== or >=).  Consider optimizing them.
-  for (int i = wildcard_only_indices_.size() - 1; i >= 0; --i) {
+  // Start by matching against all-wildcard patterns in reverse order.  Their
+  // indices are stored in reverse index order in wildcard_only_indices, so
+  // traverse it forwards.  Stop if a match is found (since earlier matches will
+  // have a smaller index and be overridden by the already-found match).
+  // TODO(jmaessen): These patterns all devolve to a string length check (== or
+  // >=).  Consider optimizing them.
+  for (int i = 0, sz = wildcard_only_indices_.size(); i < sz; ++i) {
     int index = wildcard_only_indices_[i];
     if (wildcards_[index]->Match(str)) {
       max_effective_index = effective_indices_[index];
       break;
     }
   }
+  int exit_effective_index = wildcards_.size() - 1;
   int rolling_end = str.size() - rolling_hash_length;
-  if (rolling_end >= 0) {
+  if (max_effective_index < exit_effective_index && rolling_end >= 0) {
     // Do a Rabin-Karp rolling match through the string.
     uint64 rolling_hash = RollingHash(str.data(), 0, rolling_hash_length);
-    int exit_effective_index = wildcards_.size() - 1;
       // Uses signed arithmetic for correct comparison below.
     for (int ofs = 0;
          max_effective_index < exit_effective_index && ofs <= rolling_end; ) {

pagespeed/kernel/base/fast_wildcard_group.h

@@ -93,6 +93,11 @@ don't get long, and all failed probes terminate in an empty bucket.
 
 class FastWildcardGroup {
  public:
+  // Don't generate a hash unless there are this many non-wildcard-only
+  // patterns.  Exposed for testing purposes (we can't use FRIEND_TEST here for
+  // open-source dependency reasons).
+  static const int kMinPatterns = 11;
+
   FastWildcardGroup()
       : rolling_hash_length_(kUncompiled) { }
   FastWildcardGroup(const FastWildcardGroup& src)
@@ -150,7 +155,7 @@ class FastWildcardGroup {
   // Information that is computed during compilation.
   mutable std::vector<uint64> rolling_hashes_;  // One per wildcard
   mutable std::vector<int> effective_indices_;  // One per wildcard
-  mutable std::vector<int> wildcard_only_indices_;
+  mutable std::vector<int> wildcard_only_indices_;  // Reverse order
   mutable std::vector<int> pattern_hash_index_;  // hash table
   mutable AtomicInt32 rolling_hash_length_;
 

pagespeed/kernel/base/fast_wildcard_group_test.cc

@@ -139,6 +139,54 @@ TEST_F(FastWildcardGroupTest, AppendSequenceLarge) {
   Append();
 }
 
+TEST_F(FastWildcardGroupTest, AllowDisallowCompiled) {
+  FastWildcardGroup group;
+  group.Disallow("*");
+  // Pad the group with irrelevant stuff to force it to be compiled.
+  for (int i = 0; i < FastWildcardGroup::kMinPatterns; ++i) {
+    group.Allow("a");
+  }
+  group.Allow("*");
+
+  EXPECT_TRUE(group.Match("a", true));
+  EXPECT_TRUE(group.Match("b", true));
+  EXPECT_TRUE(group.Match("c", true));
+}
+
+TEST_F(FastWildcardGroupTest, AllowDisallowCompiledLarger) {
+  FastWildcardGroup group;
+  group.Allow("*");
+  // Pad the group with irrelevant stuff to force it to be compiled.
+  for (int i = 0; i < FastWildcardGroup::kMinPatterns; ++i) {
+    group.Disallow("a");
+  }
+  group.Disallow("*");
+  for (int i = 0; i < FastWildcardGroup::kMinPatterns; ++i) {
+    group.Allow("c");
+  }
+
+  EXPECT_FALSE(group.Match("a", true));
+  EXPECT_FALSE(group.Match("b", true));
+  EXPECT_TRUE(group.Match("c", true));
+}
+
+TEST_F(FastWildcardGroupTest, AllowDisallowLargeWildcardOnly) {
+  FastWildcardGroup group;
+  group.Allow("?");
+  // Pad the group with irrelevant stuff to force it to be compiled.
+  for (int i = 0; i < FastWildcardGroup::kMinPatterns; ++i) {
+    group.Allow("aa");
+  }
+  group.Disallow("??");
+
+  EXPECT_TRUE(group.Match("a", true));
+  EXPECT_FALSE(group.Match("aa", true));
+  EXPECT_TRUE(group.Match("aaa", true));
+  EXPECT_TRUE(group.Match("a", false));
+  EXPECT_FALSE(group.Match("aa", false));
+  EXPECT_FALSE(group.Match("aaa", false));
+}
+
 TEST_F(FastWildcardGroupTest, HardCodedDefault) {
   HardCodedDefault();
 }