email_addr.nx

email_addr.nx -- RFC 5322 addr-spec validator (practical subset). The full RFC 5322 grammar accepts obscure forms like quoted local parts (\"foo bar\"@example.com), comments ((comment)), and folded whitespace -- practically never seen in real email addresses. We implement the subset that matches what users actually type: local@domain local = 1+ chars from [A-Za-z0-9!#$%&'*+-/=?^_`{|}~.] with '.' not first, not last, not consecutive domain = at least one DNS label separated by '.' label = [A-Za-z0-9] with optional [A-Za-z0-9-] interior, trailing alnum, total length 1..63 Returns (local_off, local_len, domain_off, domain_len) on success so caller can upper-case compare, hash, etc. Zero- alloc. Use cases: signup form validation, mailing-list import sanity check, abuse detection, SPF lookup prep. Invariants: EA1 Total length cap 320 bytes (RFC 5321 §4.5.3.1.3). EA2 Local part cap 64 bytes. EA3 Domain cap 255 bytes; per-label cap 63. EA4 Returns EA_ERR_* negative on violation; offsets populated even on failure up to the point of failure (useful for error messaging).