folly/test/RangeTest.cpp

   1 /*
   2  * Copyright 2013 Facebook, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *   http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 // @author Kristina Holst (kholst@fb.com)
  18 // @author Andrei Alexandrescu (andrei.alexandrescu@fb.com)
  19
  20 #include "folly/Range.h"
  21
  22 #include <limits>
  23 #include <stdlib.h>
  24 #include <string>
  25 #include <sys/mman.h>
  26 #include <boost/range/concepts.hpp>
  27 #include <gtest/gtest.h>
  28
  29 namespace folly { namespace detail {
  30
  31 // declaration of functions in Range.cpp
  32 size_t qfind_first_byte_of_memchr(const StringPiece& haystack,
  33                                   const StringPiece& needles);
  34
  35 size_t qfind_first_byte_of_byteset(const StringPiece& haystack,
  36                                    const StringPiece& needles);
  37
  38 }}  // namespaces
  39
  40 using namespace folly;
  41 using namespace std;
  42
  43 BOOST_CONCEPT_ASSERT((boost::RandomAccessRangeConcept<StringPiece>));
  44
  45 TEST(StringPiece, All) {
  46   const char* foo = "foo";
  47   const char* foo2 = "foo";
  48   string fooStr(foo);
  49   string foo2Str(foo2);
  50
  51   // we expect the compiler to optimize things so that there's only one copy
  52   // of the string literal "foo", even though we've got it in multiple places
  53   EXPECT_EQ(foo, foo2);  // remember, this uses ==, not strcmp, so it's a ptr
  54                          // comparison rather than lexical
  55
  56   // the string object creates copies though, so the c_str of these should be
  57   // distinct
  58   EXPECT_NE(fooStr.c_str(), foo2Str.c_str());
  59
  60   // test the basic StringPiece functionality
  61   StringPiece s(foo);
  62   EXPECT_EQ(s.size(), 3);
  63
  64   EXPECT_EQ(s.start(), foo);              // ptr comparison
  65   EXPECT_NE(s.start(), fooStr.c_str());   // ptr comparison
  66   EXPECT_NE(s.start(), foo2Str.c_str());  // ptr comparison
  67
  68   EXPECT_EQ(s.toString(), foo);              // lexical comparison
  69   EXPECT_EQ(s.toString(), fooStr.c_str());   // lexical comparison
  70   EXPECT_EQ(s.toString(), foo2Str.c_str());  // lexical comparison
  71
  72   EXPECT_EQ(s, foo);                      // lexical comparison
  73   EXPECT_EQ(s, fooStr);                   // lexical comparison
  74   EXPECT_EQ(s, foo2Str);                  // lexical comparison
  75   EXPECT_EQ(foo, s);
  76
  77   // check using StringPiece to reference substrings
  78   const char* foobarbaz = "foobarbaz";
  79
  80   // the full "foobarbaz"
  81   s.reset(foobarbaz, strlen(foobarbaz));
  82   EXPECT_EQ(s.size(), 9);
  83   EXPECT_EQ(s.start(), foobarbaz);
  84   EXPECT_EQ(s, "foobarbaz");
  85
  86   // only the 'foo'
  87   s.assign(foobarbaz, foobarbaz + 3);
  88   EXPECT_EQ(s.size(), 3);
  89   EXPECT_EQ(s.start(), foobarbaz);
  90   EXPECT_EQ(s, "foo");
  91
  92   // find
  93   s.reset(foobarbaz, strlen(foobarbaz));
  94   EXPECT_EQ(s.find("bar"), 3);
  95   EXPECT_EQ(s.find("ba", 3), 3);
  96   EXPECT_EQ(s.find("ba", 4), 6);
  97   EXPECT_EQ(s.find("notfound"), StringPiece::npos);
  98   EXPECT_EQ(s.find("notfound", 1), StringPiece::npos);
  99   EXPECT_EQ(s.find("bar", 4), StringPiece::npos);  // starting position too far
 100   // starting pos that is obviously past the end -- This works for std::string
 101   EXPECT_EQ(s.toString().find("notfound", 55), StringPiece::npos);
 102   EXPECT_EQ(s.find("z", s.size()), StringPiece::npos);
 103   EXPECT_EQ(s.find("z", 55), StringPiece::npos);
 104   // empty needle
 105   EXPECT_EQ(s.find(""), std::string().find(""));
 106   EXPECT_EQ(s.find(""), 0);
 107
 108   // single char finds
 109   EXPECT_EQ(s.find('b'), 3);
 110   EXPECT_EQ(s.find('b', 3), 3);
 111   EXPECT_EQ(s.find('b', 4), 6);
 112   EXPECT_EQ(s.find('o', 2), 2);
 113   EXPECT_EQ(s.find('y'), StringPiece::npos);
 114   EXPECT_EQ(s.find('y', 1), StringPiece::npos);
 115   EXPECT_EQ(s.find('o', 4), StringPiece::npos);  // starting position too far
 116   // starting pos that is obviously past the end -- This works for std::string
 117   EXPECT_EQ(s.toString().find('y', 55), StringPiece::npos);
 118   EXPECT_EQ(s.find('z', s.size()), StringPiece::npos);
 119   EXPECT_EQ(s.find('z', 55), StringPiece::npos);
 120   // null char
 121   EXPECT_EQ(s.find('\0'), std::string().find('\0'));
 122   EXPECT_EQ(s.find('\0'), StringPiece::npos);
 123
 124   // single char rfinds
 125   EXPECT_EQ(s.rfind('b'), 6);
 126   EXPECT_EQ(s.rfind('y'), StringPiece::npos);
 127   EXPECT_EQ(s.str().rfind('y'), StringPiece::npos);
 128   EXPECT_EQ(ByteRange(s).rfind('b'), 6);
 129   EXPECT_EQ(ByteRange(s).rfind('y'), StringPiece::npos);
 130   // null char
 131   EXPECT_EQ(s.rfind('\0'), s.str().rfind('\0'));
 132   EXPECT_EQ(s.rfind('\0'), StringPiece::npos);
 133
 134   // find_first_of
 135   s.reset(foobarbaz, strlen(foobarbaz));
 136   EXPECT_EQ(s.find_first_of("bar"), 3);
 137   EXPECT_EQ(s.find_first_of("ba", 3), 3);
 138   EXPECT_EQ(s.find_first_of("ba", 4), 4);
 139   EXPECT_EQ(s.find_first_of("xyxy"), StringPiece::npos);
 140   EXPECT_EQ(s.find_first_of("xyxy", 1), StringPiece::npos);
 141   // starting position too far
 142   EXPECT_EQ(s.find_first_of("foo", 4), StringPiece::npos);
 143   // starting pos that is obviously past the end -- This works for std::string
 144   EXPECT_EQ(s.toString().find_first_of("xyxy", 55), StringPiece::npos);
 145   EXPECT_EQ(s.find_first_of("z", s.size()), StringPiece::npos);
 146   EXPECT_EQ(s.find_first_of("z", 55), StringPiece::npos);
 147   // empty needle. Note that this returns npos, while find() returns 0!
 148   EXPECT_EQ(s.find_first_of(""), std::string().find_first_of(""));
 149   EXPECT_EQ(s.find_first_of(""), StringPiece::npos);
 150
 151   // single char find_first_ofs
 152   EXPECT_EQ(s.find_first_of('b'), 3);
 153   EXPECT_EQ(s.find_first_of('b', 3), 3);
 154   EXPECT_EQ(s.find_first_of('b', 4), 6);
 155   EXPECT_EQ(s.find_first_of('o', 2), 2);
 156   EXPECT_EQ(s.find_first_of('y'), StringPiece::npos);
 157   EXPECT_EQ(s.find_first_of('y', 1), StringPiece::npos);
 158   // starting position too far
 159   EXPECT_EQ(s.find_first_of('o', 4), StringPiece::npos);
 160   // starting pos that is obviously past the end -- This works for std::string
 161   EXPECT_EQ(s.toString().find_first_of('y', 55), StringPiece::npos);
 162   EXPECT_EQ(s.find_first_of('z', s.size()), StringPiece::npos);
 163   EXPECT_EQ(s.find_first_of('z', 55), StringPiece::npos);
 164   // null char
 165   EXPECT_EQ(s.find_first_of('\0'), std::string().find_first_of('\0'));
 166   EXPECT_EQ(s.find_first_of('\0'), StringPiece::npos);
 167
 168   // just "barbaz"
 169   s.reset(foobarbaz + 3, strlen(foobarbaz + 3));
 170   EXPECT_EQ(s.size(), 6);
 171   EXPECT_EQ(s.start(), foobarbaz + 3);
 172   EXPECT_EQ(s, "barbaz");
 173
 174   // just "bar"
 175   s.reset(foobarbaz + 3, 3);
 176   EXPECT_EQ(s.size(), 3);
 177   EXPECT_EQ(s, "bar");
 178
 179   // clear
 180   s.clear();
 181   EXPECT_EQ(s.toString(), "");
 182
 183   // test an empty StringPiece
 184   StringPiece s2;
 185   EXPECT_EQ(s2.size(), 0);
 186
 187   // Test comparison operators
 188   foo = "";
 189   EXPECT_LE(s, foo);
 190   EXPECT_LE(foo, s);
 191   EXPECT_GE(s, foo);
 192   EXPECT_GE(foo, s);
 193   EXPECT_EQ(s, foo);
 194   EXPECT_EQ(foo, s);
 195
 196   foo = "abc";
 197   EXPECT_LE(s, foo);
 198   EXPECT_LT(s, foo);
 199   EXPECT_GE(foo, s);
 200   EXPECT_GT(foo, s);
 201   EXPECT_NE(s, foo);
 202
 203   EXPECT_LE(s, s);
 204   EXPECT_LE(s, s);
 205   EXPECT_GE(s, s);
 206   EXPECT_GE(s, s);
 207   EXPECT_EQ(s, s);
 208   EXPECT_EQ(s, s);
 209
 210   s = "abc";
 211   s2 = "abc";
 212   EXPECT_LE(s, s2);
 213   EXPECT_LE(s2, s);
 214   EXPECT_GE(s, s2);
 215   EXPECT_GE(s2, s);
 216   EXPECT_EQ(s, s2);
 217   EXPECT_EQ(s2, s);
 218 }
 219
 220 template <class T>
 221 void expectLT(const T& a, const T& b) {
 222   EXPECT_TRUE(a < b);
 223   EXPECT_TRUE(a <= b);
 224   EXPECT_FALSE(a == b);
 225   EXPECT_FALSE(a >= b);
 226   EXPECT_FALSE(a > b);
 227
 228   EXPECT_FALSE(b < a);
 229   EXPECT_FALSE(b <= a);
 230   EXPECT_TRUE(b >= a);
 231   EXPECT_TRUE(b > a);
 232 }
 233
 234 template <class T>
 235 void expectEQ(const T& a, const T& b) {
 236   EXPECT_FALSE(a < b);
 237   EXPECT_TRUE(a <= b);
 238   EXPECT_TRUE(a == b);
 239   EXPECT_TRUE(a >= b);
 240   EXPECT_FALSE(a > b);
 241 }
 242
 243 TEST(StringPiece, EightBitComparisons) {
 244   char values[] = {'\x00', '\x20', '\x40', '\x7f', '\x80', '\xc0', '\xff'};
 245   constexpr size_t count = sizeof(values) / sizeof(values[0]);
 246   for (size_t i = 0; i < count; ++i) {
 247     std::string a(1, values[i]);
 248     // Defeat copy-on-write
 249     std::string aCopy(a.data(), a.size());
 250     expectEQ(a, aCopy);
 251     expectEQ(StringPiece(a), StringPiece(aCopy));
 252
 253     for (size_t j = i + 1; j < count; ++j) {
 254       std::string b(1, values[j]);
 255       expectLT(a, b);
 256       expectLT(StringPiece(a), StringPiece(b));
 257     }
 258   }
 259 }
 260
 261 TEST(StringPiece, ToByteRange) {
 262   StringPiece a("hello");
 263   ByteRange b(a);
 264   EXPECT_EQ(static_cast<const void*>(a.begin()),
 265             static_cast<const void*>(b.begin()));
 266   EXPECT_EQ(static_cast<const void*>(a.end()),
 267             static_cast<const void*>(b.end()));
 268
 269   // and convert back again
 270   StringPiece c(b);
 271   EXPECT_EQ(a.begin(), c.begin());
 272   EXPECT_EQ(a.end(), c.end());
 273 }
 274
 275 TEST(StringPiece, InvalidRange) {
 276   StringPiece a("hello");
 277   EXPECT_EQ(a, a.subpiece(0, 10));
 278   EXPECT_EQ(StringPiece("ello"), a.subpiece(1));
 279   EXPECT_EQ(StringPiece("ello"), a.subpiece(1, std::string::npos));
 280   EXPECT_EQ(StringPiece("ell"), a.subpiece(1, 3));
 281   EXPECT_THROW(a.subpiece(6, 7), std::out_of_range);
 282   EXPECT_THROW(a.subpiece(6), std::out_of_range);
 283
 284   std::string b("hello");
 285   EXPECT_EQ(a, StringPiece(b, 0, 10));
 286   EXPECT_EQ("ello", a.subpiece(1));
 287   EXPECT_EQ("ello", a.subpiece(1, std::string::npos));
 288   EXPECT_EQ("ell", a.subpiece(1, 3));
 289   EXPECT_THROW(a.subpiece(6, 7), std::out_of_range);
 290   EXPECT_THROW(a.subpiece(6), std::out_of_range);
 291 }
 292
 293 #if FOLLY_HAVE_CONSTEXPR_STRLEN
 294 constexpr char helloArray[] = "hello";
 295
 296 TEST(StringPiece, Constexpr) {
 297   constexpr StringPiece hello1("hello");
 298   EXPECT_EQ("hello", hello1);
 299
 300   constexpr StringPiece hello2(helloArray);
 301   EXPECT_EQ("hello", hello2);
 302 }
 303 #endif
 304
 305 TEST(StringPiece, Prefix) {
 306   StringPiece a("hello");
 307   EXPECT_TRUE(a.startsWith(""));
 308   EXPECT_TRUE(a.startsWith("h"));
 309   EXPECT_TRUE(a.startsWith('h'));
 310   EXPECT_TRUE(a.startsWith("hello"));
 311   EXPECT_FALSE(a.startsWith("hellox"));
 312   EXPECT_FALSE(a.startsWith('x'));
 313   EXPECT_FALSE(a.startsWith("x"));
 314
 315   {
 316     auto b = a;
 317     EXPECT_TRUE(b.removePrefix(""));
 318     EXPECT_EQ("hello", b);
 319   }
 320   {
 321     auto b = a;
 322     EXPECT_TRUE(b.removePrefix("h"));
 323     EXPECT_EQ("ello", b);
 324   }
 325   {
 326     auto b = a;
 327     EXPECT_TRUE(b.removePrefix('h'));
 328     EXPECT_EQ("ello", b);
 329   }
 330   {
 331     auto b = a;
 332     EXPECT_TRUE(b.removePrefix("hello"));
 333     EXPECT_EQ("", b);
 334   }
 335   {
 336     auto b = a;
 337     EXPECT_FALSE(b.removePrefix("hellox"));
 338     EXPECT_EQ("hello", b);
 339   }
 340   {
 341     auto b = a;
 342     EXPECT_FALSE(b.removePrefix("x"));
 343     EXPECT_EQ("hello", b);
 344   }
 345   {
 346     auto b = a;
 347     EXPECT_FALSE(b.removePrefix('x'));
 348     EXPECT_EQ("hello", b);
 349   }
 350 }
 351
 352 TEST(StringPiece, Suffix) {
 353   StringPiece a("hello");
 354   EXPECT_TRUE(a.endsWith(""));
 355   EXPECT_TRUE(a.endsWith("o"));
 356   EXPECT_TRUE(a.endsWith('o'));
 357   EXPECT_TRUE(a.endsWith("hello"));
 358   EXPECT_FALSE(a.endsWith("xhello"));
 359   EXPECT_FALSE(a.endsWith("x"));
 360   EXPECT_FALSE(a.endsWith('x'));
 361
 362   {
 363     auto b = a;
 364     EXPECT_TRUE(b.removeSuffix(""));
 365     EXPECT_EQ("hello", b);
 366   }
 367   {
 368     auto b = a;
 369     EXPECT_TRUE(b.removeSuffix("o"));
 370     EXPECT_EQ("hell", b);
 371   }
 372   {
 373     auto b = a;
 374     EXPECT_TRUE(b.removeSuffix('o'));
 375     EXPECT_EQ("hell", b);
 376   }
 377   {
 378     auto b = a;
 379     EXPECT_TRUE(b.removeSuffix("hello"));
 380     EXPECT_EQ("", b);
 381   }
 382   {
 383     auto b = a;
 384     EXPECT_FALSE(b.removeSuffix("xhello"));
 385     EXPECT_EQ("hello", b);
 386   }
 387   {
 388     auto b = a;
 389     EXPECT_FALSE(b.removeSuffix("x"));
 390     EXPECT_EQ("hello", b);
 391   }
 392   {
 393     auto b = a;
 394     EXPECT_FALSE(b.removeSuffix('x'));
 395     EXPECT_EQ("hello", b);
 396   }
 397 }
 398
 399 TEST(StringPiece, PrefixEmpty) {
 400   StringPiece a;
 401   EXPECT_TRUE(a.startsWith(""));
 402   EXPECT_FALSE(a.startsWith("a"));
 403   EXPECT_FALSE(a.startsWith('a'));
 404   EXPECT_TRUE(a.removePrefix(""));
 405   EXPECT_EQ("", a);
 406   EXPECT_FALSE(a.removePrefix("a"));
 407   EXPECT_EQ("", a);
 408   EXPECT_FALSE(a.removePrefix('a'));
 409   EXPECT_EQ("", a);
 410 }
 411
 412 TEST(StringPiece, SuffixEmpty) {
 413   StringPiece a;
 414   EXPECT_TRUE(a.endsWith(""));
 415   EXPECT_FALSE(a.endsWith("a"));
 416   EXPECT_FALSE(a.endsWith('a'));
 417   EXPECT_TRUE(a.removeSuffix(""));
 418   EXPECT_EQ("", a);
 419   EXPECT_FALSE(a.removeSuffix("a"));
 420   EXPECT_EQ("", a);
 421   EXPECT_FALSE(a.removeSuffix('a'));
 422   EXPECT_EQ("", a);
 423 }
 424
 425 TEST(qfind, UInt32_Ranges) {
 426   vector<uint32_t> a({1, 2, 3, 260, 5});
 427   vector<uint32_t> b({2, 3, 4});
 428
 429   auto a_range = folly::Range<const uint32_t*>(&a[0], a.size());
 430   auto b_range = folly::Range<const uint32_t*>(&b[0], b.size());
 431
 432   EXPECT_EQ(qfind(a_range, b_range), string::npos);
 433
 434   a[3] = 4;
 435   EXPECT_EQ(qfind(a_range, b_range), 1);
 436 }
 437
 438 template <typename NeedleFinder>
 439 class NeedleFinderTest : public ::testing::Test {
 440  public:
 441   static size_t find_first_byte_of(StringPiece haystack, StringPiece needles) {
 442     return NeedleFinder::find_first_byte_of(haystack, needles);
 443   }
 444 };
 445
 446 struct SseNeedleFinder {
 447   static size_t find_first_byte_of(StringPiece haystack, StringPiece needles) {
 448     // This will only use the SSE version if it is supported on this CPU
 449     // (selected using ifunc).
 450     return detail::qfind_first_byte_of(haystack, needles);
 451   }
 452 };
 453
 454 struct NoSseNeedleFinder {
 455   static size_t find_first_byte_of(StringPiece haystack, StringPiece needles) {
 456     return detail::qfind_first_byte_of_nosse(haystack, needles);
 457   }
 458 };
 459
 460 struct MemchrNeedleFinder {
 461   static size_t find_first_byte_of(StringPiece haystack, StringPiece needles) {
 462     return detail::qfind_first_byte_of_memchr(haystack, needles);
 463   }
 464 };
 465
 466 struct ByteSetNeedleFinder {
 467   static size_t find_first_byte_of(StringPiece haystack, StringPiece needles) {
 468     return detail::qfind_first_byte_of_byteset(haystack, needles);
 469   }
 470 };
 471
 472 typedef ::testing::Types<SseNeedleFinder, NoSseNeedleFinder, MemchrNeedleFinder,
 473                          ByteSetNeedleFinder> NeedleFinders;
 474 TYPED_TEST_CASE(NeedleFinderTest, NeedleFinders);
 475
 476 TYPED_TEST(NeedleFinderTest, Null) {
 477   { // null characters in the string
 478     string s(10, char(0));
 479     s[5] = 'b';
 480     string delims("abc");
 481     EXPECT_EQ(5, this->find_first_byte_of(s, delims));
 482   }
 483   { // null characters in delim
 484     string s("abc");
 485     string delims(10, char(0));
 486     delims[3] = 'c';
 487     delims[7] = 'b';
 488     EXPECT_EQ(1, this->find_first_byte_of(s, delims));
 489   }
 490   { // range not terminated by null character
 491     string buf = "abcdefghijklmnopqrstuvwxyz";
 492     StringPiece s(buf.data() + 5, 3);
 493     StringPiece delims("z");
 494     EXPECT_EQ(string::npos, this->find_first_byte_of(s, delims));
 495   }
 496 }
 497
 498 TYPED_TEST(NeedleFinderTest, DelimDuplicates) {
 499   string delims(1000, 'b');
 500   EXPECT_EQ(1, this->find_first_byte_of("abc", delims));
 501   EXPECT_EQ(string::npos, this->find_first_byte_of("ac", delims));
 502 }
 503
 504 TYPED_TEST(NeedleFinderTest, Empty) {
 505   string a = "abc";
 506   string b = "";
 507   EXPECT_EQ(string::npos, this->find_first_byte_of(a, b));
 508   EXPECT_EQ(string::npos, this->find_first_byte_of(b, a));
 509   EXPECT_EQ(string::npos, this->find_first_byte_of(b, b));
 510 }
 511
 512 TYPED_TEST(NeedleFinderTest, Unaligned) {
 513   // works correctly even if input buffers are not 16-byte aligned
 514   string s = "0123456789ABCDEFGH";
 515   for (int i = 0; i < s.size(); ++i) {
 516     StringPiece a(s.c_str() + i);
 517     for (int j = 0; j < s.size(); ++j) {
 518       StringPiece b(s.c_str() + j);
 519       EXPECT_EQ((i > j) ? 0 : j - i, this->find_first_byte_of(a, b));
 520     }
 521   }
 522 }
 523
 524 // for some algorithms (specifically those that create a set of needles),
 525 // we check for the edge-case of _all_ possible needles being sought.
 526 TYPED_TEST(NeedleFinderTest, Needles256) {
 527   string needles;
 528   const auto minValue = std::numeric_limits<StringPiece::value_type>::min();
 529   const auto maxValue = std::numeric_limits<StringPiece::value_type>::max();
 530   // make the size ~big to avoid any edge-case branches for tiny haystacks
 531   const int haystackSize = 50;
 532   for (int i = minValue; i <= maxValue; i++) {  // <=
 533     needles.push_back(i);
 534   }
 535   EXPECT_EQ(StringPiece::npos, this->find_first_byte_of("", needles));
 536   for (int i = minValue; i <= maxValue; i++) {
 537     EXPECT_EQ(0, this->find_first_byte_of(string(haystackSize, i), needles));
 538   }
 539
 540   needles.append("these are redundant characters");
 541   EXPECT_EQ(StringPiece::npos, this->find_first_byte_of("", needles));
 542   for (int i = minValue; i <= maxValue; i++) {
 543     EXPECT_EQ(0, this->find_first_byte_of(string(haystackSize, i), needles));
 544   }
 545 }
 546
 547 TYPED_TEST(NeedleFinderTest, Base) {
 548   for (int i = 0; i < 32; ++i) {
 549     for (int j = 0; j < 32; ++j) {
 550       string s = string(i, 'X') + "abca" + string(i, 'X');
 551       string delims = string(j, 'Y') + "a" + string(j, 'Y');
 552       EXPECT_EQ(i, this->find_first_byte_of(s, delims));
 553     }
 554   }
 555 }
 556
 557 const size_t kPageSize = 4096;
 558 // Updates contents so that any read accesses past the last byte will
 559 // cause a SIGSEGV.  It accomplishes this by changing access to the page that
 560 // begins immediately after the end of the contents (as allocators and mmap()
 561 // all operate on page boundaries, this is a reasonable assumption).
 562 // This function will also initialize buf, which caller must free().
 563 void createProtectedBuf(StringPiece& contents, char** buf) {
 564   ASSERT_LE(contents.size(), kPageSize);
 565   const size_t kSuccess = 0;
 566   if (kSuccess != posix_memalign((void**)buf, kPageSize, 4 * kPageSize)) {
 567     ASSERT_FALSE(true);
 568   }
 569   mprotect(*buf + kPageSize, kPageSize, PROT_NONE);
 570   size_t newBegin = kPageSize - contents.size();
 571   memcpy(*buf + newBegin, contents.data(), contents.size());
 572   contents.reset(*buf + newBegin, contents.size());
 573 }
 574
 575 void freeProtectedBuf(char* buf) {
 576   mprotect(buf + kPageSize, kPageSize, PROT_READ | PROT_WRITE);
 577   free(buf);
 578 }
 579
 580 TYPED_TEST(NeedleFinderTest, NoSegFault) {
 581   const string base = string(32, 'a') + string("b");
 582   const string delims = string(32, 'c') + string("b");
 583   for (int i = 0; i <= 32; i++) {
 584     for (int j = 0; j <= 33; j++) {
 585       for (int shouldFind = 0; shouldFind <= 1; ++shouldFind) {
 586         StringPiece s1(base);
 587         s1.advance(i);
 588         ASSERT_TRUE(!s1.empty());
 589         if (!shouldFind) {
 590           s1.pop_back();
 591         }
 592         StringPiece s2(delims);
 593         s2.advance(j);
 594         char* buf1;
 595         char* buf2;
 596         createProtectedBuf(s1, &buf1);
 597         createProtectedBuf(s2, &buf2);
 598         // printf("s1: '%s' (%ld) \ts2: '%s' (%ld)\n",
 599         //        string(s1.data(), s1.size()).c_str(), s1.size(),
 600         //        string(s2.data(), s2.size()).c_str(), s2.size());
 601         auto r1 = this->find_first_byte_of(s1, s2);
 602         auto f1 = std::find_first_of(s1.begin(), s1.end(),
 603                                      s2.begin(), s2.end());
 604         auto e1 = (f1 == s1.end()) ? StringPiece::npos : f1 - s1.begin();
 605         EXPECT_EQ(r1, e1);
 606         auto r2 = this->find_first_byte_of(s2, s1);
 607         auto f2 = std::find_first_of(s2.begin(), s2.end(),
 608                                      s1.begin(), s1.end());
 609         auto e2 = (f2 == s2.end()) ? StringPiece::npos : f2 - s2.begin();
 610         EXPECT_EQ(r2, e2);
 611         freeProtectedBuf(buf1);
 612         freeProtectedBuf(buf2);
 613       }
 614     }
 615   }
 616 }
 617