Summary:
`escapeString` is very slow even when there's very little to nothing to escape. This diff adds a fast path to copy sequences of bytes that don't need escaping.
It also optimizes appending escape sequences: `string::push_back` is slow because it has to do a capacity check for every character.
Before:
```
============================================================================
folly/test/JsonOtherTest.cpp relative time/iter iters/s
============================================================================
jsonSerialize 818.55ns 1.22M
jsonSerializeWithNonAsciiEncoding 1.35us 738.06K
jsonSerializeWithUtf8Validation 1.42us 705.60K
jsonSerializeAsciiWithUtf8Validation 3.27us 306.06K
parseSmallStringWithUtf 1.91us 522.38K
parseNormalString 1.51us 660.27K
parseBigString 384.44ns 2.60M
toJson 480.54ns 2.08M
============================================================================
```
After:
```
============================================================================
folly/test/JsonOtherTest.cpp relative time/iter iters/s
============================================================================
jsonSerialize 781.69ns 1.28M
jsonSerializeWithNonAsciiEncoding 847.68ns 1.18M
jsonSerializeWithUtf8Validation 928.68ns 1.08M
jsonSerializeAsciiWithUtf8Validation 199.85ns 5.00M
parseSmallStringWithUtf 1.93us 518.39K
parseNormalString 1.45us 689.11K
parseBigString 378.66ns 2.64M
toJson 446.38ns 2.24M
============================================================================
```
All string escaping benchmarks are slightly faster, and ASCII-only with no escapes is 8x faster.
Reviewed By: luciang, evilmucedin, yfeldblum
Differential Revision:
D4793233
fbshipit-source-id:
c40d07708bd787799c8c00f9f23a417b862ee9ae
#include <folly/json.h>
#include <algorithm>
-#include <cassert>
#include <functional>
+#include <type_traits>
-#include <boost/next_prior.hpp>
#include <boost/algorithm/string.hpp>
+#include <boost/next_prior.hpp>
+#include <folly/Bits.h>
+#include <folly/Portability.h>
#include <folly/Conv.h>
#include <folly/Range.h>
dynamic parseNumber(Input& in);
dynamic parseObject(Input& in) {
- assert(*in == '{');
+ DCHECK_EQ(*in, '{');
++in;
dynamic ret = dynamic::object;
}
dynamic parseArray(Input& in) {
- assert(*in == '[');
+ DCHECK_EQ(*in, '[');
++in;
dynamic ret = dynamic::array;
}
std::string parseString(Input& in) {
- assert(*in == '\"');
+ DCHECK_EQ(*in, '\"');
++in;
std::string ret;
return ret;
}
+// Fast path to determine the longest prefix that can be left
+// unescaped in a string of sizeof(T) bytes packed in an integer of
+// type T.
+template <class T>
+size_t firstEscapableInWord(T s) {
+ static_assert(std::is_unsigned<T>::value, "Unsigned integer required");
+ constexpr T kOnes = ~T() / 255; // 0x...0101
+ constexpr T kMsbs = kOnes * 0x80; // 0x...8080
+
+ // Sets the MSB of bytes < b. Precondition: b < 128.
+ auto isLess = [](T w, uint8_t b) {
+ // A byte is < b iff subtracting b underflows, so we check that
+ // the MSB wasn't set before and it's set after the subtraction.
+ return (w - kOnes * b) & ~w & kMsbs;
+ };
+
+ auto isChar = [&](uint8_t c) {
+ // A byte is == c iff it is 0 if xored with c.
+ return isLess(s ^ (kOnes * c), 1);
+ };
+
+ // The following masks have the MSB set for each byte of the word
+ // that satisfies the corresponding condition.
+ auto isHigh = s & kMsbs; // >= 128
+ auto isLow = isLess(s, 0x20); // <= 0x1f
+ auto needsEscape = isHigh | isLow | isChar('\\') | isChar('"');
+
+ if (!needsEscape) {
+ return sizeof(T);
+ }
+
+ if (folly::kIsLittleEndian) {
+ return folly::findFirstSet(needsEscape) / 8 - 1;
+ } else {
+ return sizeof(T) - folly::findLastSet(needsEscape) / 8;
+ }
+}
+
// Escape a string so that it is legal to print it in JSON text.
void escapeString(
StringPiece input,
auto* e = reinterpret_cast<const unsigned char*>(input.end());
while (p < e) {
+ // Find the longest prefix that does not need escaping, and copy
+ // it literally into the output string.
+ auto firstEsc = p;
+ while (firstEsc < e) {
+ auto avail = e - firstEsc;
+ uint64_t word = 0;
+ if (avail >= 8) {
+ word = folly::loadUnaligned<uint64_t>(firstEsc);
+ } else {
+ memcpy(static_cast<void*>(&word), firstEsc, avail);
+ }
+ auto prefix = firstEscapableInWord(word);
+ DCHECK_LE(prefix, avail);
+ firstEsc += prefix;
+ if (prefix < 8) {
+ break;
+ }
+ }
+ if (firstEsc > p) {
+ out.append(reinterpret_cast<const char*>(p), firstEsc - p);
+ p = firstEsc;
+ // We can't be in the middle of a multibyte sequence, so we can reset q.
+ q = p;
+ if (p == e) {
+ break;
+ }
+ }
+
+ // Handle the next byte that may need escaping.
+
// Since non-ascii encoding inherently does utf8 validation
// we explicitly validate utf8 only if non-ascii encoding is disabled.
if ((opts.validate_utf8 || opts.skip_invalid_utf8)
&& !opts.encode_non_ascii) {
- // to achieve better spatial and temporal coherence
+ // To achieve better spatial and temporal coherence
// we do utf8 validation progressively along with the
- // string-escaping instead of two separate passes
+ // string-escaping instead of two separate passes.
- // as the encoding progresses, q will stay at or ahead of p
- CHECK(q >= p);
+ // As the encoding progresses, q will stay at or ahead of p.
+ CHECK_GE(q, p);
- // as p catches up with q, move q forward
+ // As p catches up with q, move q forward.
if (q == p) {
// calling utf8_decode has the side effect of
// checking that utf8 encodings are valid
// note that this if condition captures utf8 chars
// with value > 127, so size > 1 byte
char32_t v = utf8ToCodePoint(p, e, opts.skip_invalid_utf8);
- out.append("\\u");
- out.push_back(hexDigit(uint8_t(v >> 12)));
- out.push_back(hexDigit((v >> 8) & 0x0f));
- out.push_back(hexDigit((v >> 4) & 0x0f));
- out.push_back(hexDigit(v & 0x0f));
+ char buf[] = "\\u\0\0\0\0";
+ buf[2] = hexDigit(uint8_t(v >> 12));
+ buf[3] = hexDigit((v >> 8) & 0x0f);
+ buf[4] = hexDigit((v >> 4) & 0x0f);
+ buf[5] = hexDigit(v & 0x0f);
+ out.append(buf, 6);
} else if (*p == '\\' || *p == '\"') {
- out.push_back('\\');
- out.push_back(char(*p++));
+ char buf[] = "\\\0";
+ buf[1] = char(*p++);
+ out.append(buf, 2);
} else if (*p <= 0x1f) {
switch (*p) {
case '\b': out.append("\\b"); p++; break;
case '\r': out.append("\\r"); p++; break;
case '\t': out.append("\\t"); p++; break;
default:
- // note that this if condition captures non readable chars
+ // Note that this if condition captures non readable chars
// with value < 32, so size = 1 byte (e.g control chars).
- out.append("\\u00");
- out.push_back(hexDigit(uint8_t((*p & 0xf0) >> 4)));
- out.push_back(hexDigit(uint8_t(*p & 0xf)));
+ char buf[] = "\\u00\0\0";
+ buf[4] = hexDigit(uint8_t((*p & 0xf0) >> 4));
+ buf[5] = hexDigit(uint8_t(*p & 0xf));
+ out.append(buf, 6);
p++;
}
} else {
#include <folly/json.h>
#include <folly/Benchmark.h>
+#include <folly/Conv.h>
#include <folly/FileUtil.h>
+#include <folly/Range.h>
#include <folly/portability/GFlags.h>
#include <folly/portability/GTest.h>
using folly::parseJson;
using folly::toJson;
+constexpr folly::StringPiece kLargeAsciiString =
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
+ "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk";
+
+constexpr folly::StringPiece kLargeNonAsciiString =
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
+ "qwerty \xc2\x80 \xef\xbf\xbf poiuy";
+
TEST(Json, StripComments) {
const std::string kTestDir = "folly/test/";
const std::string kTestFile = "json_test_data/commented.json";
}
BENCHMARK(jsonSerialize, iters) {
+ const dynamic obj = kLargeNonAsciiString;
+
folly::json::serialization_opts opts;
for (size_t i = 0; i < iters; ++i) {
- folly::json::serialize(
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy",
- opts);
+ folly::json::serialize(obj, opts);
}
}
BENCHMARK(jsonSerializeWithNonAsciiEncoding, iters) {
+ const dynamic obj = kLargeNonAsciiString;
+
folly::json::serialization_opts opts;
opts.encode_non_ascii = true;
for (size_t i = 0; i < iters; ++i) {
- folly::json::serialize(
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy",
- opts);
+ folly::json::serialize(obj, opts);
}
}
BENCHMARK(jsonSerializeWithUtf8Validation, iters) {
+ const dynamic obj = kLargeNonAsciiString;
+
folly::json::serialization_opts opts;
opts.validate_utf8 = true;
for (size_t i = 0; i < iters; ++i) {
- folly::json::serialize(
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy"
- "qwerty \xc2\x80 \xef\xbf\xbf poiuy",
- opts);
+ folly::json::serialize(obj, opts);
+ }
+}
+
+BENCHMARK(jsonSerializeAsciiWithUtf8Validation, iters) {
+ const dynamic obj = kLargeAsciiString;
+
+ folly::json::serialization_opts opts;
+ opts.validate_utf8 = true;
+
+ for (size_t i = 0; i < iters; ++i) {
+ folly::json::serialize(obj, opts);
}
}
}
BENCHMARK(parseBigString, iters) {
+ const auto json = folly::to<std::string>('"', kLargeAsciiString, '"');
+
for (size_t i = 0; i < iters; ++i) {
- parseJson("\""
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "akjhfk jhkjlakjhfk jhkjlakjhfk jhkjl akjhfk"
- "\"");
+ parseJson(json);
}
}
R"("\b\f\n\r\u0001\t\\\"/\u000b\u0007")");
}
+TEST(Json, EscapeCornerCases) {
+ // The escaping logic uses some bitwise operations to determine
+ // which bytes need escaping 8 bytes at a time. Test that this logic
+ // is correct regardless of positions by planting 2 characters that
+ // may need escaping at each possible position and checking the
+ // result, for varying string lengths.
+
+ folly::json::serialization_opts opts;
+ opts.validate_utf8 = true;
+
+ std::string s;
+ std::string expected;
+ for (bool ascii : {true, false}) {
+ opts.encode_non_ascii = ascii;
+
+ for (size_t len = 2; len < 32; ++len) {
+ for (size_t i = 0; i < len; ++i) {
+ for (size_t j = 0; j < len; ++j) {
+ if (i == j) {
+ continue;
+ }
+
+ s.clear();
+ expected.clear();
+
+ expected.push_back('"');
+ for (size_t pos = 0; pos < len; ++pos) {
+ if (pos == i) {
+ s.push_back('\\');
+ expected.append("\\\\");
+ } else if (pos == j) {
+ s.append("\xe2\x82\xac");
+ expected.append(ascii ? "\\u20ac" : "\xe2\x82\xac");
+ } else {
+ s.push_back('x');
+ expected.push_back('x');
+ }
+ }
+ expected.push_back('"');
+
+ EXPECT_EQ(folly::json::serialize(s, opts), expected) << ascii;
+ }
+ }
+ }
+ }
+}
+
TEST(Json, JsonNonAsciiEncoding) {
folly::json::serialization_opts opts;
opts.encode_non_ascii = true;