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Check each distinct string and float range once in the full image check

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The full check scanned the contents of every string node and every float token over its own range, so many nodes pointing to one large range made load() quadratic. The structural walk now only collects the ranges; after it, each kind is sorted and checked once per distinct range. Ranges of one kind that overlap without being identical are rejected, as save() never writes them (nodes that share a value share the whole range). The cost is linear in the size of the image plus sorting the ranges.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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Niels Lohmann committed 2026-10-09 16:25:34 +02:00
1 parent 8018ac65de
commit 91d90e2b31
4 files changed
+308 -54
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tests/src/unit-json_view_image.cpp
+105
View File
@@ -712,6 +712,111 @@ TEST_CASE("json_view images: check")
}
}
SECTION("nodes that share a range")
{
// [big string, then n strings made to point to the big string]: every
// node shares the one range (the check reads it once)
const std::size_t n = 200;
std::string long_text = "[\"" + std::string(5000, 'a') + "\"";
for (std::size_t k = 0; k < n; ++k)
{
long_text += ",\"x\"";
}
long_text += "]";
const std::vector<std::uint8_t> img = json_document::parse(long_text).save();
const node big = node_at(img, 1);
std::vector<std::uint8_t> b = img;
for (std::size_t k = 0; k < n; ++k)
{
set_node(b, 2 + k, big);
}
CHECK(load_result(b, image_check::full).empty());
const json_document d = json_document::load(b);
CHECK(d.root().size() == n + 1);
CHECK(d.root()[n].get<std::string>() == std::string(5000, 'a'));
CHECK(d.root().dump() == json_document::load(b, image_check::none).root().dump());
// the same for decoded strings and float tokens, with a node that
// records another digit layout than its token
const std::vector<std::uint8_t> img2 = json_document::parse(R"(["a\"b", "a\"b", 1.25, 1.25, 1.25e3])").save();
CHECK(load_result(img2, image_check::full).empty());
std::vector<std::uint8_t> same = img2;
set_node(same, 2, node_at(img2, 1));
set_node(same, 4, node_at(img2, 3));
CHECK(load_result(same, image_check::full).empty());
CHECK(json_document::load(same).root().dump() == R"(["a\"b","a\"b",1.25,1.25,1250.0])");
std::vector<std::uint8_t> layout = same;
node f4 = node_at(layout, 4);
f4.extra = 0x0100u; // the layout of "1.", and not that of "1.25"
set_node(layout, 4, f4);
rejected(layout, false);
f4.extra = 0xFFFFu; // "many" digits: fine, as compaction writes it
set_node(layout, 4, f4);
CHECK(load_result(layout, image_check::full).empty());
}
SECTION("ranges that overlap")
{
// save() writes every string and every token to a place of its own
// (nodes that share a value share the whole range): ranges that
// overlap without being identical are a damaged image, though each
// range is a valid string or token
// nodes: 0 [ 1 "abcdef" 2 "ghijkl" 3 1.2525 4 9.9 5 "a\"bcd" (decoded) 6 "e\"fgh" (decoded)
const std::vector<std::uint8_t> img = json_document::parse(R"(["abcdef", "ghijkl", 1.2525, 9.9, "a\"bcd", "e\"fgh"])").save();
REQUIRE(load_result(img, image_check::full).empty());
// node i with the range (off of node of + shift, length), and extra
const auto aliased = [&](std::size_t i, std::size_t of, std::uint32_t shift, std::uint32_t length, std::uint16_t extra)
{
std::vector<std::uint8_t> b = img;
node n = node_at(b, of);
n.off += shift;
n.len = length;
n.extra = extra;
set_node(b, i, n);
return b;
};
// source strings
rejected(aliased(2, 1, 0, 4, 0), false); // "abcd": the start of another string
rejected(aliased(2, 1, 1, 4, 0), false); // "bcde": inside
rejected(aliased(2, 1, 2, 4, 0), false); // "cdef": the end
CHECK(load_result(aliased(2, 1, 0, 6, 0), image_check::full).empty()); // the whole range: identical
// decoded strings: inside, and partially overlapping (the arena holds a"bcde"fgh)
rejected(aliased(6, 5, 1, 3, 0), false);
rejected(aliased(6, 5, 3, 5, 0), false);
CHECK(load_result(aliased(6, 5, 0, 5, 0), image_check::full).empty());
// float tokens: "1.25" and "525" (an integer token as a float) inside "1.2525"
rejected(aliased(4, 3, 0, 4, 0x0201u), false);
rejected(aliased(4, 3, 3, 3, 0x0003u), false);
CHECK(load_result(aliased(4, 3, 0, 6, 0x0401u), image_check::full).empty());
// a string and a float token may use the same bytes (each is checked by its own kind)
std::vector<std::uint8_t> shared = img;
node as_string = node_at(img, 2);
as_string.off = node_at(img, 3).off;
as_string.len = 6;
set_node(shared, 2, as_string);
CHECK(load_result(shared, image_check::full).empty());
// empty strings inside others are not ranges
CHECK(load_result(aliased(2, 1, 2, 0, 0), image_check::full).empty());
}
SECTION("copies within an edited document")
{
// copies within a document share the value: identical ranges
json_editable_document d = json_editable_document::parse(R"({"s": "ab", "e": "x\"y", "f": 1.5, "g": 1.5e300, "a": [1.5, "ab"]})");
d.set(d.root(), "c1", d.root()["a"]);
d.set(d.root(), "c2", d.root()["a"]);
d.set(d.root(), "c3", d.root());
d.push_back(d.root()["a"], d.root()["e"]);
d.push_back(d.root()["a"], d.root()["g"]);
d.push_back(d.root()["a"], d.root()["g"]);
d.set(d.root()["s"], "changed");
d.set(d.root()["f"], 7.25);
const std::vector<std::uint8_t> saved = d.save();
CHECK(load_result(saved, image_check::full).empty());
CHECK(json_document::load(saved).root().dump() == d.root().dump());
check_round_trip(d);
}
SECTION("integer ranges")
{
// tokens of many digits, which the parser stores as floats