core: switch JSON library from jsoncpp to nlohmann/json#2918
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Replace the compiled jsoncpp dependency with the header-only nlohmann/json (v3.11.3, already present transitively via libevents). - Parse paths use the non-throwing json::parse(..., allow_exceptions=false) with predicate-guarded access to stay abort-free under -fno-exceptions. - Rework the MavlinkDirect serializer (libmav_receiver) onto nlohmann::ordered_json + dump(), which fixes a latent string-escaping bug and renders NaN/Inf as null, while preserving field order. - Migrate mission import and component metadata (parse and serialize) and the system tests accordingly. - Update build wiring, packaging (.pc, CMake config, debian), CI, docs, and the mavlink_direct_sender example.
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PARAM_EXT_{VALUE,SET,ACK}.param_value is declared as char[128] in the
MAVLink definition but the extended-parameter protocol uses it to carry
the raw bytes of a typed value. libmav treats char[] as a NUL-terminated
string (getString/strnlen), so any value containing a zero byte is
truncated on receive, and the bytes are usually not valid UTF-8.
Represent these fields (via an explicit, documented allow-list) as JSON
byte arrays, read as raw bytes so nothing is truncated. The field stays
declared char, so the message CRC_EXTRA is unchanged and wire
compatibility is preserved. The parse direction already accepts a number
array for char[] fields, so this round-trips.
Add a system test covering the round-trip (including an interior NUL) and
adapt the param-change-notification collector, which previously read
param_value as a string.
JonasVautherin
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Jul 13, 2026
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Just a small nitpick, feel free to ignore 🙈
…d lookup The binary char[] allow-list used a function-local static std::set<std::pair<std::string, std::string>>. Such a static has a runtime destructor that runs at process exit on the main thread, while a lingering io-context thread may still be serializing a message and calling find() on it -- the MAVLink fuzzer caught this as a heap-use-after-free. Replace the set with a constexpr std::array of std::string_view literals: no static object with a destructor, and no per-lookup heap allocation of a temporary pair. Behaviour is unchanged.
This was referenced Jul 13, 2026
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What
Replace the compiled jsoncpp dependency with the header-only nlohmann/json (v3.11.3, already present transitively via
libevents).Why
ExternalProjectto build and link.std::ostringstreamconcatenation.dump()escapes correctly and rendersNaN/Infasnull.How
-fno-exceptions): parse via the non-throwingjson::parse(..., allow_exceptions=false)+is_discarded(), with predicate-guarded access so nlohmann never hits itsabort()path.libmav_receiver): reworked ontonlohmann::ordered_json+dump(), preserving field order (plainjsonwould sort keys).libmav_conversions,mission_import,mavlink_component_metadata,component_metadata_server_impl, and the system tests.third_party/nlohmann_json, removedjsoncpp+Findjsoncpp.cmake), packaging (.pc, CMake config,debian/control— header-only, so runtime dep dropped), CI, docs, and the example.Testing
build-debugandbuild-server-debugboth build cleanly..planfixtures + component metadata).