package idna

ocaml-idna

Internationalized Domain Names for OCaml (IDNA 2008 and UTS #46).

Pure OCaml implementation of IDNA2008 hostname validation, UTS #46 compatibility processing, Punycode encoding/decoding, and Unicode NFC normalization. No C dependencies. Unicode 16.0.0.

Installation

opam install idna

Usage

(* UTS #46 processing *)
Idna.to_ascii "Königsgäßchen.example"   (* Ok "xn--knigsgchen-b4a3dun.example" *)
Idna.to_unicode "xn--maana-pta.com"     (* Ok "mañana.com" *)

(* IDNA2008 validation *)
Idna.is_valid_hostname "example.com"     (* true *)
Idna.is_valid_hostname "-invalid.com"    (* false *)

Idna.check_label "xn--maana-pta"        (* Ok () *)
Idna.check_label "xn--X"                (* Error "invalid punycode" *)

(* Punycode *)
Idna.Punycode.decode "maana-pta"         (* Ok [0x6D; 0x61; 0xF1; ...] *)
Idna.Punycode.encode [0x6D;0x61;0xF1;0x61;0x6E;0x61]  (* Ok "maana-pta" *)

(* NFC normalization *)
Idna.nfc [0x0065; 0x0301]               (* [0x00E9] — e + acute → é *)

Features

• UTS #46 Nontransitional processing (to_ascii, to_unicode)
• IDNA2008 hostname and label validation (RFC 5890, 5891, 5892)
• Bidirectional text rules 1-6 (RFC 5893), domain-level enforcement
• Punycode encoding and decoding (RFC 3492)
• Unicode NFC normalization (canonical decomposition, ordering, composition; Hangul)
• Codepoint classification (PVALID, CONTEXTJ, CONTEXTO)
• CONTEXTJ/CONTEXTO contextual rules
• STD3 ASCII rules

Regenerating Unicode tables

Tables are generated from Unicode 16.0.0 UCD:

./tools/download_ucd.sh 16.0.0
python3 tools/gen_tables.py --output lib/idna_tables.ml

License

ISC