Files
logos-protocol/cpp/implementations
Dario LipicarandClaude Opus 5 362b03fb1e feat(codec): one canonical LIDL ↔ JSON codec, generic over composition (#29)
* feat(codec): one canonical LIDL <-> JSON codec, generic over composition

The tagged-bytes encoding {"_bytes": "<base64url, unpadded>"} was implemented
SIX times — the Qt conversion here, the plain wire's json_mapping, the lp helper
in logos-cpp-sdk, a copy emitted into every generated cdylib module, the Rust
SDK and the Python client — and they disagreed on which inputs they accept:

  - {"_bytes":"AA","x":1} decoded as BYTES on the lp path (no size()==1 check)
    but as a MAP on the plain wire and in the glue.
  - Padded "AH-A_w==" gave correct bytes in one copy, empty in another, None in
    Rust.
  - A plain string / number / number-array argument was accepted by C++
    providers (Qt and CLI parity) and rejected by Rust ones.

logos_codec.h is the single implementation. Leaves: tstr, bstr, every signed and
unsigned integral spelling, every floating spelling, bool, any (recursion stops).
Composition is GENERIC — std::vector<T> and std::map/unordered_map<std::string,T>
for any supported T, at any depth — so [bstr], [[bstr]], {tstr: [bstr]} and bytes
nested in a map all encode canonically without anything enumerating combinations.

Codec<T> is a trait, so an unsupported T is an incomplete type: a compile error
naming the type, never a silent fallback. Decode throws CodecError carrying the
path ("[0][1]", ".k") instead of substituting a default — a mangled value must
not reach business logic. bstr keeps a documented lenient form for provider-side
arguments, because the Qt consumer path and the logoscore CLI both produce plain
strings and number arrays for byte parameters.

JsonArg exists for generated dispatch: it converts itself into whatever the
callee's parameter type is. Naming the type instead is a trap — spelling [uint]
as std::vector<uint64_t> (the LIDL mapping) does not bind to an author's
std::vector<uint32_t>, since distinct vector instantiations do not convert.

logos_codec.h joins the installed header set; nix/include.nix already globs
cpp/*.h.

Tests: 198/198. 15 new ones pin the contract rather than the happy path —
[[bstr]] tagged at depth, map-of-bytes, empty elements surviving as elements,
uint64 past 2^63, an integral JSON number decoding as float64, padded base64,
the multi-key {"_bytes":...} case being a map, and path-carrying failures.

Not yet converged onto this header (follow-ups): the Qt conversion in
logos_json_convert.cpp, and the plain wire's copy in json_mapping.cpp — the
latter needs a strict variant first, because it THROWS on malformed base64
(via its own logos::plain::CodecError) where every other copy is tolerant.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* refactor(codec): fold the Qt and plain-wire copies into the shared codec

The two remaining in-repo implementations now delegate:

  - logos_json_convert.cpp (the Qt CONSUMER path — argument encoding and return
    decoding) dropped Qt's toBase64/fromBase64 and its own tagged-bytes
    predicate. Only the QByteArray <-> std::vector<uint8_t> hop stays local, so
    the Qt path cannot drift from the wire or from providers: same alphabet, same
    padding rule, same single-key shape.
  - implementations/plain/json_mapping.cpp dropped its anonymous-namespace
    b64url_encode/decode.

The wire needed something the tolerant decode does not give it: it REJECTS a
corrupt frame rather than silently decoding fewer bytes. Hence
b64UrlDecodeChecked — strict about the alphabet and the length, tolerant of '='
padding — which json_mapping uses to keep throwing its own
logos::plain::CodecError. Consumer-facing decodes stay tolerant. Both behaviours
now come from one implementation instead of four that disagreed.

Also removed the local isTaggedBytes wrapper, which shadowed the shared one and
made unqualified calls ambiguous.

Tests: 199/199, with the strict decode's accept/reject set pinned (padding
tolerated, stray character rejected, impossible length rejected).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
2026-07-28 15:01:49 -03:00
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