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Speed up JSON pointer parsing, formatting, comparison and lookup (#5836)
* Speed up JSON pointer parsing, formatting, comparison and lookup Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Restore unflatten() speed after the linear-time rewrite The prefix tree introduced for linear unflatten() kept a std::map per prefix, copied each token into it and looked every token up a second time while creating the values. Replace the per-prefix maps by one open-addressing table keyed by (parent, token) that refers to the parsed tokens, skip the lookups for the prefix shared with the previous key (flattened objects are mostly sorted), and derive the prefix numbers of the second pass from parent links instead of lookups. Time and memory stay linear in the pointer depth, and the result is still independent of the iteration order of the flattened object. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Put [[noreturn]] before __attribute__ on the JSON pointer throw helpers Clang 18 on Linux rejects a C++11 attribute list after a GNU __attribute__ ("an attribute list cannot appear here"). Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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@@ -23,10 +23,14 @@ using nlohmann::json;
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using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
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#endif
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#include <cerrno>
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#include <cstdlib>
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#include <limits>
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#include <map>
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#include <random>
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#include <sstream>
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#include <string>
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#include <vector>
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#include <sstream>
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TEST_CASE("JSON pointers")
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{
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@@ -1123,3 +1127,192 @@ TEST_CASE("flatten of ordered_json")
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CHECK(ordered_json::array().flatten() == ordered_json({{"", nullptr}}));
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}
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}
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namespace
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{
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// reference implementation of the array index rules (RFC 6901, Sect. 4) based on strtoull
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enum class index_class
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{
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ok,
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leading_zero,
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not_a_number,
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unresolved,
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exceeds_size_type
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};
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index_class classify_index(const std::string& s, std::size_t& idx)
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{
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if (s.size() > 1 && s[0] == '0')
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{
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return index_class::leading_zero;
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}
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if (!s.empty() && s != "-" && !(s[0] >= '0' && s[0] <= '9'))
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{
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return index_class::not_a_number;
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}
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char* end = nullptr;
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errno = 0;
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const unsigned long long res = std::strtoull(s.c_str(), &end, 10); // NOLINT(runtime/int)
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if (end == s.c_str() || errno == ERANGE || static_cast<std::size_t>(end - s.c_str()) != s.size())
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{
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return index_class::unresolved;
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}
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if (res >= static_cast<unsigned long long>((std::numeric_limits<std::size_t>::max)())) // NOLINT(runtime/int)
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{
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return index_class::exceeds_size_type;
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}
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idx = static_cast<std::size_t>(res);
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return index_class::ok;
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}
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// the observable behavior of json_pointer::at() and contains() for an array index token
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void check_index_token(const std::string& token)
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{
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const json array = {10, 20, 30};
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const json::json_pointer ptr("/" + token);
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std::size_t idx = 0;
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const auto cls = classify_index(token, idx);
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const bool exists = cls == index_class::ok && idx < array.size();
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CAPTURE(token)
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CHECK(array.contains(ptr) == (exists && token != "-"));
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if (token == "-")
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{
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CHECK_THROWS_AS(array.at(ptr), json::out_of_range&);
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return;
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}
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switch (cls)
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{
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case index_class::leading_zero:
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CHECK_THROWS_AS(array.at(ptr), json::parse_error&);
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break;
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case index_class::not_a_number:
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CHECK_THROWS_AS(array.at(ptr), json::parse_error&);
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break;
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case index_class::unresolved:
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case index_class::exceeds_size_type:
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CHECK_THROWS_AS(array.at(ptr), json::out_of_range&);
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break;
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case index_class::ok:
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default:
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if (exists)
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{
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CHECK(array.at(ptr) == array[idx]);
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}
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else
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{
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CHECK_THROWS_AS(array.at(ptr), json::out_of_range&);
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}
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break;
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}
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}
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} // namespace
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TEST_CASE("JSON pointer array index tokens match strtoull semantics")
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{
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SECTION("boundary values")
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{
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const std::string max_digits = std::to_string((std::numeric_limits<std::size_t>::max)());
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const std::vector<std::string> tokens =
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{
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"", "-", "0", "1", "2", "3", "00", "01", "007", "+1", "-1", " 1", "1 ", "1a", "a1", "0x1", "1e1", "1.0",
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"999999999", "1000000000", "99999999999999999", "999999999999999999", "1000000000000000000",
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"9999999999999999999", "18446744073709551614", max_digits, "18446744073709551616",
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"99999999999999999999999", "000000000000000000000"
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};
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for (const auto& token : tokens)
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{
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check_index_token(token);
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}
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}
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SECTION("random tokens")
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{
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std::mt19937 gen(42);
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const std::string alphabet = "0123456789012345678901234567890123456789-+ ex";
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for (int i = 0; i < 5000; ++i)
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{
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std::string token(static_cast<std::size_t>(gen() % 23), '0');
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for (auto& c : token)
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{
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c = alphabet[gen() % alphabet.size()];
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}
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check_index_token(token);
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}
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}
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}
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TEST_CASE("JSON pointer operations on pointers with escaped tokens")
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{
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const std::vector<std::string> strings =
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{
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"", "/", "//", "/a", "/a/b", "/a~1b", "/~0", "/~01", "/~10", "/a~0~1/b/", "/0/1/2", "/ ", "/a/", "/~1/~0"
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};
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for (const auto& str : strings)
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{
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CAPTURE(str)
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const json::json_pointer ptr(str);
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CHECK(ptr.to_string() == str);
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CHECK(ptr / "x" / "y" / std::size_t{3} == json::json_pointer(str + "/x/y/3"));
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CHECK(ptr.parent_pointer() == (str.empty() ? ptr : json::json_pointer(str.substr(0, str.rfind('/')))));
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// comparison with a string, in place, and with every other pointer
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#if !defined(JSON_TEST_DEPRECATED_FUNCTIONS_DELETED)
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for (const auto& other : strings)
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{
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CAPTURE(other)
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CHECK((ptr == other) == (str == other));
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CHECK((other == ptr) == (str == other));
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CHECK((ptr != other) == (str != other));
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}
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CHECK_THROWS_AS(ptr == "x", json::parse_error&);
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CHECK_THROWS_AS(ptr == "/~", json::parse_error&);
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CHECK_THROWS_AS(ptr == "/b/~2", json::parse_error&);
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#endif
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}
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}
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TEST_CASE("JSON pointer lookups")
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{
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json j = {{"a", {{"b", {1, 2, 3}}}}, {"", 7}, {"~/", {{"x", nullptr}}}};
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const json& cj = j;
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CHECK(cj[json::json_pointer("/a/b/2")] == 3);
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CHECK(cj.at(json::json_pointer("/a/b/1")) == 2);
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CHECK(cj.at(json::json_pointer("/")) == 7);
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CHECK(cj.contains(json::json_pointer("/~0~1/x")));
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CHECK(!cj.contains(json::json_pointer("/a/c")));
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CHECK(cj.value(json::json_pointer("/a/b/0"), 5) == 1);
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CHECK(cj.value(json::json_pointer("/a/b/3"), 5) == 5);
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CHECK(cj.value(json::json_pointer("/a/zz"), 5) == 5);
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CHECK_THROWS_AS(cj.at(json::json_pointer("/a/c")), json::out_of_range&);
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CHECK_THROWS_AS(cj.at(json::json_pointer("/a/b/3")), json::out_of_range&);
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// non-const access reuses existing entries and creates missing ones
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j[json::json_pointer("/a/b/1")] = 20;
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j[json::json_pointer("/n/m")] = 1;
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CHECK(j["a"]["b"] == json({1, 20, 3}));
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CHECK(j["n"]["m"] == 1);
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}
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TEST_CASE("JSON patch with moves and copies")
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{
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json doc = {{"a", {{"b", {1, 2, 3}}}}, {"c", {{"d", "x"}}}};
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CHECK(doc.patch(json::parse(R"([{"op":"move","from":"/a/b","path":"/c/e"}])")) ==
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json::parse(R"({"a":{},"c":{"d":"x","e":[1,2,3]}})"));
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CHECK(doc.patch(json::parse(R"([{"op":"copy","from":"/a/b","path":"/c/e"}])")) ==
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json::parse(R"({"a":{"b":[1,2,3]},"c":{"d":"x","e":[1,2,3]}})"));
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CHECK(doc.patch(json::parse(R"([{"op":"move","from":"/a/b/0","path":"/a/b/2"}])")) ==
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json::parse(R"({"a":{"b":[2,3,1]},"c":{"d":"x"}})"));
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// a failing move leaves a copy-patched document untouched
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CHECK_THROWS_AS(doc.patch(json::parse(R"([{"op":"move","from":"","path":""}])")), json::out_of_range&);
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json inplace = doc;
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CHECK_THROWS_AS(inplace.patch_inplace(json::parse(R"([{"op":"move","from":"","path":""}])")), json::out_of_range&);
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CHECK(inplace == doc);
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}
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