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Fix to_bjdata() emitting unparsable output when _ArraySize_ is not an array (#5455)

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* Fix to_bjdata() emitting unparsable output when _ArraySize_ is not an array

write_bjdata_ndarray() never checked that _ArraySize_ is an array. The shape
is written verbatim as the header length, so a null shape emitted 'Z' and an
object shape emitted '{' after the '#', neither of which from_bjdata()
accepts, and the round-trip guarantee in the BJData docs was broken.

Both slipped through the existing validation: for null, empty() is true so
the element count starts at 0 and the per-dimension loop never runs, and for
an object the loop walks its values, which can satisfy the non-negative
integer check. When _ArrayData_ then matched that count, the writer took the
ndarray path.

Require the shape to be an array, so anything else falls back to a plain
object encoding that round-trips, as the fallback rule in the docs already
specifies.

Signed-off-by: qatcod <79017227+qatcod@users.noreply.github.com>

* Document that _ArraySize_ must be an array in the ndarray requirements

The list at bjdata.md is the exhaustive set of conditions for the ndarray
encoding, but it only implied this one through 'every entry of'.

Signed-off-by: qatcod <79017227+qatcod@users.noreply.github.com>

---------

Signed-off-by: qatcod <79017227+qatcod@users.noreply.github.com>
This commit is contained in:
Qatadaha Bin Matloob
2026-09-05 20:30:22 +02:00
committed by GitHub
parent dd26d3ff07
commit 09b6b6b5ba
4 changed files with 44 additions and 0 deletions
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tests/src/unit-bjdata.cpp
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@@ -2751,6 +2751,31 @@ TEST_CASE("BJData")
CHECK(json::to_bjdata(j_ok) == std::vector<uint8_t>({'[', '$', 'U', '#', '[', 'i', 2, 'i', 3, ']', 1, 2, 3, 4, 5, 6}));
CHECK(json::from_bjdata(json::to_bjdata(j_ok), true, true) == j_ok);
}
SECTION("ndarray whose _ArraySize_ is not an array stays as object")
{
// the shape is written verbatim as the header length, so a
// value that is not an array cannot produce a valid one: null
// would emit 'Z' and an object '{', neither of which a reader
// accepts after '#'. Both have to stay plain objects.
json const j_null = json({{"_ArrayType_", "uint8"}, {"_ArraySize_", nullptr}, {"_ArrayData_", json::array()}});
const auto out_null = json::to_bjdata(j_null);
CHECK(out_null.at(0) == '{');
CHECK(json::from_bjdata(out_null) == j_null);
// an object shape passes the per-entry check by iterating its
// values rather than dimensions, so it needs rejecting too
json const j_obj = json({{"_ArrayType_", "uint8"}, {"_ArraySize_", {{"a", 1}}}, {"_ArrayData_", {1}}});
const auto out_obj = json::to_bjdata(j_obj);
CHECK(out_obj.at(0) == '{');
CHECK(json::from_bjdata(out_obj) == j_obj);
// a scalar shape is not a dimension list either
json const j_num = json({{"_ArrayType_", "uint8"}, {"_ArraySize_", 1}, {"_ArrayData_", {1}}});
const auto out_num = json::to_bjdata(j_num);
CHECK(out_num.at(0) == '{');
CHECK(json::from_bjdata(out_num) == j_num);
}
}
}