Throw type_error.321 when serializing discarded values to binary formats (#5761)

* Throw type_error.321 when serializing discarded values to binary formats

The CBOR, MessagePack, UBJSON, BJData, and BSON writers silently
skipped the payload of a value_t::discarded value nested in an array
or object, while still writing its slot in the element/member count
(and, for BSON, its entry header), producing a binary document whose
declared size does not match what was actually written.

Throw type_error.321 instead, for a discarded value anywhere in the
tree, including at the top level.

Rewritten from the original PR against the current (non-recursive
option aside) binary_writer.hpp, which has changed substantially since
this was first proposed; the out_of_range.412 MessagePack size check
and unrelated test reformatting from that PR are dropped as out of
scope here.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Document and test type_error.321 for discarded binary values

Add docs for the new exception (home/exceptions.md and the Exceptions
sections of to_cbor/to_msgpack/to_ubjson/to_bjdata/to_bson) and test
coverage for a discarded value nested in an array or object, nested
deeper, and (for UBJSON/BJData) inside an optimized same-type array,
for each of CBOR, MessagePack, UBJSON, BJData, and BSON. Adjust the
three pre-existing "discarded" tests that asserted the old silent
behavior (empty/short output) to expect type_error.321 instead.

Co-authored-by: ameliabarnabyhub <312084480+ameliabarnabyhub@users.noreply.github.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: ameliabarnabyhub <ameliabarnabyhub@users.noreply.github.com>
Co-authored-by: ameliabarnabyhub <312084480+ameliabarnabyhub@users.noreply.github.com>
This commit is contained in:
Niels Lohmann
2026-10-06 07:33:34 +02:00
committed by GitHub
co-authored by ameliabarnabyhub ameliabarnabyhub
parent 8a142bc436
commit 5379e04ce4
13 changed files with 329 additions and 25 deletions
+59 -5
View File
@@ -35,10 +35,59 @@ TEST_CASE("UBJSON")
{
SECTION("discarded")
{
// discarded values are not serialized
// a discarded value cannot be serialized to UBJSON
json const j = json::value_t::discarded;
const auto result = json::to_ubjson(j);
CHECK(result.empty());
CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
}
SECTION("discarded values nested in a container")
{
json const discarded = json::value_t::discarded;
SECTION("in an array")
{
json const j = {1, discarded, 2};
#if JSON_DIAGNOSTICS
CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] (/1) cannot serialize discarded value to UBJSON", json::type_error&);
#else
CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
#endif
}
SECTION("as an object value")
{
json j;
j["a"] = 1;
j["b"] = discarded;
#if JSON_DIAGNOSTICS
CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] (/b) cannot serialize discarded value to UBJSON", json::type_error&);
#else
CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
#endif
}
SECTION("nested deeper (array in object in array)")
{
json inner_array = {1, discarded};
json middle_object;
middle_object["x"] = inner_array;
json const j = {middle_object};
#if JSON_DIAGNOSTICS
CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] (/0/x/1) cannot serialize discarded value to UBJSON", json::type_error&);
#else
CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
#endif
}
SECTION("optimized array of all-discarded elements")
{
json const j = {discarded, discarded};
#if JSON_DIAGNOSTICS
CHECK_THROWS_WITH_AS(json::to_ubjson(j, true, true), "[json.exception.type_error.321] (/0) cannot serialize discarded value to UBJSON", json::type_error&);
#else
CHECK_THROWS_WITH_AS(json::to_ubjson(j, true, true), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
#endif
}
}
SECTION("null")
@@ -2099,9 +2148,14 @@ TEST_CASE("UBJSON")
SECTION("discarded")
{
// a discarded value cannot be serialized to UBJSON, even as part
// of an optimized array of a single (here: valueless) type
json const j = {json::value_t::discarded, json::value_t::discarded};
std::vector<uint8_t> expected = {'[', '$', 'N', '#', 'i', 2};
CHECK(json::to_ubjson(j, true, true) == expected);
#if JSON_DIAGNOSTICS
CHECK_THROWS_WITH_AS(json::to_ubjson(j, true, true), "[json.exception.type_error.321] (/0) cannot serialize discarded value to UBJSON", json::type_error&);
#else
CHECK_THROWS_WITH_AS(json::to_ubjson(j, true, true), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
#endif
}
}
}