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Cover the bulk string and UTF-8 scanners
These paths had no dedicated tests and rested on differential fuzzing only. Add three sections, all comparing the contiguous scanner against the byte-at-a-time one on the parsed value and on the exact error message: - every string of length 1..3 over an alphabet of ordinary ASCII, both specials, a control byte, escape characters, UTF-8 lead and continuation bytes, and a byte that is never valid - each at offset 0 and offset 9, so the bulk scanner sees them with and without a run behind them - every kind of run-ending byte at each offset across two 8-byte SWAR words, so multibyte sequences also straddle the word boundary - the boundaries of every range validate_one_utf8() recognizes: shortest and longest encodings, overlongs, both ends of the surrogate block, U+10FFFF and just past it, and truncated sequences Verified to fail if the bulk validator accepts surrogates, and if the SWAR word test stops detecting control characters. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
@@ -416,3 +416,169 @@ TEST_CASE("lexer number fast path")
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"syntax error while parsing array - unexpected number literal; expected ']'");
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}
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}
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TEST_CASE("lexer string fast path")
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{
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// Build a byte string from explicit values: a hex escape in a string
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// literal swallows every following hex digit, which makes sequences like
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// "\xC3\xA9b" mean something other than they look like.
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const auto bytes = [](std::initializer_list<int> values)
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{
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std::string result;
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for (const int value : values)
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{
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result.push_back(static_cast<char>(value));
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}
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return result;
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};
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// the full outcome of parsing @a doc: the parsed value, or the exact error
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// message, so a mismatch in either is caught
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const auto outcome = [](const std::string & doc, bool streaming)
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{
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try
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{
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if (streaming)
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{
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std::stringstream ss(doc);
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const json j = json::parse(ss);
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return j.dump();
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}
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const json j = json::parse(doc);
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return j.dump();
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}
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// not just parse_error: if a bulk scanner ever let ill-formed UTF-8
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// through, dump() would throw type_error.316, and that has to surface
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// as a reported mismatch rather than as an uncaught exception
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catch (const json::exception& e)
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{
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return std::string(e.what());
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}
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};
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SECTION("exhaustive contiguous vs streaming parity")
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{
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// ordinary ASCII, both specials, a control byte, characters that make
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// the preceding backslash a valid escape, a UTF-8 lead byte of each
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// length, a continuation byte, and a byte that is never valid
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const std::vector<std::string> alphabet =
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{
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"a", "\"", "\\", "n", "u", "0", bytes({0x01}),
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bytes({0xC3}), bytes({0xA9}), bytes({0xE4}), bytes({0xF0}),
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bytes({0x80}), bytes({0xFF})
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};
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std::vector<std::string> mismatches;
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std::vector<std::string> tokens{""};
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for (std::size_t length = 1; length <= 3; ++length)
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{
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std::vector<std::string> next;
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next.reserve(tokens.size() * alphabet.size());
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for (const auto& prefix : tokens)
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{
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for (const auto& symbol : alphabet)
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{
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next.push_back(prefix + symbol);
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}
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}
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tokens = next;
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for (const auto& token : tokens)
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{
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// once at the start of the string, once past the first 8-byte
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// SWAR word so the bulk scanner has a run behind it
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for (const std::size_t offset : {static_cast<std::size_t>(0), static_cast<std::size_t>(9)})
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{
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const std::string doc = "[\"" + std::string(offset, 'a') + token + "\"]";
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if (outcome(doc, false) != outcome(doc, true))
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{
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mismatches.push_back(doc);
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}
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}
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}
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}
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// 13 + 169 + 2197 tokens, each at two offsets
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CHECK(tokens.size() == 2197);
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CAPTURE(mismatches);
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CHECK(mismatches.empty());
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}
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SECTION("special bytes at every offset of the SWAR stride")
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{
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// The bulk scanner consumes 8 bytes at a time and then a tail; place
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// every kind of byte that ends a run at each offset across two words,
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// so multibyte sequences also straddle the word boundary.
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const std::vector<std::string> specials =
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{
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"\"", "\\", bytes({0x01}), bytes({0x1F}), bytes({0x7F}),
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bytes({0xC3, 0xA9}), bytes({0xE4, 0xB8, 0xAD}), bytes({0xF0, 0x9F, 0x98, 0x80}),
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bytes({0xFF}), bytes({0xC3}), bytes({0xE4, 0xB8})
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};
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std::vector<std::string> mismatches;
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for (std::size_t offset = 0; offset <= 17; ++offset)
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{
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for (const auto& special : specials)
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{
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const std::string doc = "[\"" + std::string(offset, 'a') + special + "\"]";
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if (outcome(doc, false) != outcome(doc, true))
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{
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mismatches.push_back(doc);
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}
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}
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}
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CAPTURE(mismatches);
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CHECK(mismatches.empty());
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}
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SECTION("UTF-8 ranges are accepted and rejected as documented")
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{
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// The bulk validator must accept exactly what the byte-at-a-time
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// scanner accepts, so pin the boundaries of every range it recognizes.
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struct utf8_case
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{
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std::string sequence;
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bool valid;
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const char* description;
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};
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const std::vector<utf8_case> cases =
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{
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{bytes({0xC2, 0x80}), true, "U+0080, shortest two-byte"},
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{bytes({0xDF, 0xBF}), true, "U+07FF, longest two-byte"},
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{bytes({0xC1, 0xBF}), false, "overlong two-byte"},
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{bytes({0xC2, 0x7F}), false, "two-byte with bad continuation"},
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{bytes({0xE0, 0xA0, 0x80}), true, "U+0800, shortest three-byte"},
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{bytes({0xE0, 0x9F, 0xBF}), false, "overlong three-byte"},
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{bytes({0xED, 0x9F, 0xBF}), true, "U+D7FF, just below the surrogates"},
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{bytes({0xED, 0xA0, 0x80}), false, "surrogate U+D800"},
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{bytes({0xED, 0xBF, 0xBF}), false, "surrogate U+DFFF"},
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{bytes({0xEE, 0x80, 0x80}), true, "U+E000, just above the surrogates"},
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{bytes({0xEF, 0xBF, 0xBF}), true, "U+FFFF"},
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{bytes({0xF0, 0x90, 0x80, 0x80}), true, "U+10000, shortest four-byte"},
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{bytes({0xF0, 0x8F, 0xBF, 0xBF}), false, "overlong four-byte"},
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{bytes({0xF4, 0x8F, 0xBF, 0xBF}), true, "U+10FFFF, highest code point"},
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{bytes({0xF4, 0x90, 0x80, 0x80}), false, "above U+10FFFF"},
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{bytes({0xF5, 0x80, 0x80, 0x80}), false, "lead byte out of range"},
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{bytes({0x80}), false, "bare continuation byte"},
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{bytes({0xFF}), false, "byte that never appears in UTF-8"},
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{bytes({0xC3}), false, "truncated two-byte"},
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{bytes({0xE4, 0xB8}), false, "truncated three-byte"},
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{bytes({0xF0, 0x9F, 0x98}), false, "truncated four-byte"}
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};
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for (const auto& test_case : cases)
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{
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CAPTURE(test_case.description);
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// at the start of the string and past the first SWAR word, so the
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// sequence is seen by the bulk scanner and by its tail
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for (const std::size_t offset : {static_cast<std::size_t>(0), static_cast<std::size_t>(9)})
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{
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CAPTURE(offset);
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const std::string doc = "[\"" + std::string(offset, 'a') + test_case.sequence + "\"]";
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CHECK(json::accept(doc) == test_case.valid);
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CHECK(outcome(doc, false) == outcome(doc, true));
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}
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}
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}
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}
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