feat(receive): add maxsize argument to bound memory usage

client:receive("*l") and receive("*a") are unbounded: a peer that never
sends a newline, or never closes, makes LuaSocket buffer until the
process runs out of memory (e.g. src/http.lua reading response headers
in a loop). Add an optional maxsize argument that caps the payload a
single call may accumulate, including prefix.

- Hoist all argument validation ahead of timeout_markstart() so bad
  calls (maxsize < 1, #prefix >= maxsize, numeric pattern > maxsize)
  raise before any I/O and leave the socket untouched.
- recvline/recvall take a budget and return a new internal
  BUF_OVERSIZED code, surfaced to Lua as the "oversized" error
  alongside "timeout"/"closed", with the partial held in the 3rd
  return value.
- recvraw is left untouched: argument checks make the cap unreachable
  for numeric patterns.
- Preserve three invariants: a timeout partial is always shorter than
  maxsize (safe to retry as prefix), completion beats the cap for *a,
  and no bytes are lost or skipped on overflow.
- tcp.c, unixstream.c and serial.c all share this code path unchanged.

Adds test coverage (argument errors, *l/*a boundaries, timeout/close
at the cap, the drain idiom, numeric patterns, unix-stream mirror) and
documents the new argument, error, and recovery idioms in docs/tcp.html.

0 files changed, 0 insertions, 0 deletions