Skip to contents

Normalize hosts to canonical comparison form

Source: R/normalize.R
host_normalize.Rd

Converts DNS hostnames to their canonical comparison form following the ratified canonical-host normalization contract: Unicode NFC, case mapping, UTS-46 label mapping and validation (non-transitional, with `UseSTD3ASCIIRules`, `CheckHyphens`, `CheckBidi`, and `CheckJoiners`), conversion to lowercase ASCII A-labels, and DNS length verification, while preserving whether the input carried a single terminal root dot.

Usage

host_normalize(
  x,
  check_hyphens = TRUE,
  use_std3 = TRUE,
  verify_dns_length = TRUE
)

Arguments

x

Character vector of hostnames. `NA` elements pass through as `NA` (missing, not invalid). Names are preserved.

check_hyphens

Logical scalar. When `TRUE` (the default) the UTS #46 `CheckHyphens` rule rejects `"–"` in the 3rd/4th positions and leading or trailing hyphens. `FALSE` drops that check.

use_std3

Logical scalar. When `TRUE` (the default) `UseSTD3ASCIIRules` restricts ASCII to letters, digits, and hyphen. `FALSE` admits other ASCII (e.g. `"_"`) that the pinned table marks STD3-disallowed-but-valid.

verify_dns_length

Logical scalar. When `TRUE` (the default) each A-label must be 1-63 octets and the whole host <= 253. `FALSE` drops the length limits (empty labels are still rejected as structural errors).

Value

A character vector the same length as `x`. Each element is the canonical lowercase ASCII A-label host, or `NA_character_` when the input is `NA` or invalid under the profile.

Details

Unlike [puny_encode()], invalid input is reported by returning `NA_character_` (never by aborting), so a caller can layer its own policy. The profile is fixed at one pinned Unicode version per release; see [normalization_profile_info()] for the machine-readable identity.

This is a **UTS #46 profile, not IDNA2008 / RFC 5891 conformance.** UTS #46 is compatibility processing and deliberately differs from IDNA2008 — it accepts labels IDNA2008 would reject (e.g. `"☕.example"` becomes `"xn–53h.example"`). The pipeline draws on RFC 3492 (the Punycode transform), NFC per UAX #15, the RFC 5892 ContextJ rules via `CheckJoiners` (ZWJ/ZWNJ only — full RFC 5892 CONTEXTO is **not** checked), the RFC 5893 Bidi rule via `CheckBidi`, and STD 3 (RFC 952 + RFC 1123) host-name rules via `UseSTD3ASCIIRules`. IDNA2003 / Nameprep (RFC 3490/3491/3454) is not used.

The default applies the full strict UTS #46 profile (`uts46-nontransitional-std3-v1`). The `check_hyphens`, `use_std3`, and `verify_dns_length` arguments are UTS #46 processing flags that can each be relaxed independently; pass the *same* values to [normalization_profile_info()] to obtain the identity of the resulting profile. These are standard UTS #46 parameters, **not** a browser mode: `CheckBidi` and `CheckJoiners` always apply and are never knobs, and full WHATWG host policy (where `beStrict = false` flips exactly these three) lives upstack in `rurl`, not here.

See also

[normalization_profile_info()] for the profile identity, [puny_encode()] for the lower-level RFC 3492 transform.

Examples

host_normalize(c("Example.COM", "münchen.de", "example.com."))
#> [1] "example.com"       "xn--mnchen-3ya.de" "example.com."     
host_normalize("a_b.com") # NA: STD3 rejects "_"
#> [1] NA
host_normalize("a_b.com", use_std3 = FALSE) # "a_b.com"
#> [1] "a_b.com"