codegen: inline 1-byte LEN fast path for string/bytes decode
Singular and repeated string/bytes fields in generated full-mode _decode
now read the length byte and dispatch in-line instead of calling
wire.decode_string / wire.decode_bytes. For length < 128 (the common
short-string RPC case), the path stays inside the parent JIT trace:
no child-trace stitch, no per-element function frame, utf8_len lookup
hoisted to a generated-file upvalue.
The original a6n design — one ffi.cast(U8CP, buf) at the top of each
_decode — was abandoned: the cdata wrapper is 24 bytes per call and
LuaJIT can't sink the allocation because the pointer local lives
across wire.decode_* call frames. Net regression at small sizes
(+11-16%) overwhelmed the single-byte-read savings.
Bench (hello.Person full-mode decode):
size ns/op before ns/op after delta
10B 419 390 -6.9%
100B 515 478 -7.2%
1KB 9004 8042 -10.7%
10KB 64644 56745 -12.2%
100KB 625638 537750 -14.0%
Zero allocation impact across all sizes. Tests: 1043 pass, 37 JIT
trace gates pass. (a6n)
c_runtime: encode/decode singular sub-messages (ra6 3d)
Refactor encode_lua/decode_lua into encode_body/decode_body so the
field-walk loop is callable recursively, then dispatch the MESSAGE
kind into a per-side sub-handler. Repeated and map fields still skip
at the field-walk level — 3e (jc9) and 3h (asz) land them next.
encode_submessage_field force-establishes the parent enc_buf's
heap_idx via a no-op ebuf_grow before recursing. Without that the
final ebuf_reserve on the parent could land its new userdata above
sub-encode's leaked stack slots, making the closing lua_settop drop
the parent's heap.
decode_submessage_field bounds the inner read by temporarily
shrinking c->len to the sub-message end offset; the wire-prim
helpers already bounds-check against c->len, so a malformed inner
payload can't over-read into the outer message's bytes.
New fixture test/proto/c_nested.proto carries a 5-level singular
chain (L1->L2->L3->L4->L5) for the depth test. The two existing
"skip message" tests are renamed to "skip repeated and map" — sub-
messages now encode and decode end-to-end.
bd-hwe