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Get URL hosts

Source: R/accessors.R
get_host.Rd

Extracts the host component of a URL.

Usage

get_host(
  url,
  protocol_handling = "keep",
  www_handling = "none",
  source = c("all", "private", "icann"),
  subdomain_levels_to_keep = NULL,
  case_handling = c("lower", "keep", "upper", "lower_host"),
  host_encoding = c("keep", "idna", "unicode"),
  scheme_policy = c("infer", "require"),
  scheme_acceptance = c("web", "general"),
  url_standard = NULL,
  engine = NULL
)

Arguments

url

A character vector of URLs.

protocol_handling

A character string specifying how to handle protocols. Defaults to "keep". Regardless of this option, rurl only processes authority-based URLs whose scheme is one of http, https, ftp, or ftps; a scheme-bearing input with any other scheme (e.g. mailto:, tel:, ws:) yields parse_status = "error". Scheme inference (below) also requires the input to be host-shaped: a scheme-less string that is not a host (e.g. "asdfghjkl", "12345", "/path") or is a non-canonical IP literal (integer/hex/octal/short forms, or leading-zero octets like "192.168.010.1") is rejected as "error" rather than having a scheme fabricated for it.

  • "keep": If a supported scheme exists (http, https, ftp, ftps), it's used. If no scheme and the input is host-shaped, "http://" is added; otherwise the input is not a URL and yields "error".

  • "none": If a supported scheme exists, it's used. If no scheme, then no scheme is used (scheme component will be NA).

  • "strip": Any existing scheme is removed (scheme component will be NA).

  • "http": The scheme is forced to be "http".

  • "https": The scheme is forced to be "https".

www_handling

A character string specifying how to handle "www" and www[number] prefixes in the host. Defaults to "none".

  • "none": (Default) Leaves the host's www prefix (or lack thereof) untouched.

  • "strip": Removes any "www." or www[number]. prefix.

  • "keep": Ensures the host starts with "www.". If it has www[number]., it's normalized to "www.". If no www prefix, "www." is added. An empty input host remains empty.

  • "if_no_subdomain": If the host is a bare registered domain (e.g., "example.com"), "www." is added. If the host already has a "www." or www[number]. prefix, it is normalized to "www." (e.g., "www1.example.com" becomes "www.example.com"; "www1.sub.example.com" becomes "www.sub.example.com"). If a non-www subdomain exists (e.g., "sub.example.com" or the normalized "www.sub.example.com"), the host is not further altered. An empty input host remains empty.

source

Which PSL source to use: "all", "private", or "icann". Subdomain trimming depends on which section is consulted, so pass source = "icann" to exclude private suffixes (e.g. github.io).

subdomain_levels_to_keep

An integer or NULL. Determines how many levels of subdomains are kept, in addition to any 'www.' prefix handled by www_handling.

  • NULL: (Default) No specific subdomain stripping is performed beyond www_handling.

  • 0: All subdomains are stripped. If www_handling preserved or added 'www.', it remains (e.g., 'www.sub.example.com' becomes 'www.example.com'; 'sub.example.com' becomes 'example.com').

  • N > 0: Keeps up to N levels of subdomains, counted from right-to-left (closest to the registered domain), in addition to any 'www.' prefix. E.g., if N=1, 'three.two.one.example.com' becomes 'one.example.com'; 'www.three.two.one.example.com' (post www_handling) becomes 'www.one.example.com'.

case_handling

How to handle casing of the returned host. Defaults to "lower".

host_encoding

How to present the host in clean_url. Defaults to "keep".

  • "keep": Leave host as parsed by curl (may preserve original case).

  • "idna": Convert Unicode host labels to Punycode (IDNA) for the cleaned URL.

  • "unicode": Decode Punycode labels to Unicode for the cleaned URL.

scheme_policy

Controls whether scheme-less, host-shaped input is accepted (an input-acceptance axis, distinct from protocol_handling, which only controls how the scheme is presented, and from url_standard, which controls interpretation). Defaults to "infer".

  • "infer": (Default) Fabricate http:// for scheme-less host-shaped input (e.g. example.com parses as http://example.com), a browser-omnibox-style affordance. This is the historical behavior.

  • "require": Reject scheme-less input — a scheme-less host-shaped value becomes parse_status = "error" rather than gaining a fabricated scheme. Use this for a strict, pure-parser posture. Note this governs only bare host input; scheme-relative //host input is governed separately by scheme_relative_handling.

scheme_acceptance

Which scheme tokens may enter parsing (a scheme-acceptance axis, distinct from scheme_policy, which governs scheme-less input, and from url_standard, which governs interpretation). Defaults to "web".

  • "web": (Default) Only the curated web-scheme allowlist (http/https/ftp/ftps/file) is admitted; a scheme-bearing input outside it is parse_status = "error". This is the historical, byte-for-byte compatible behavior.

  • "general": Admit any syntactically valid scheme token and parse opaque (mailto:x), non-special (foo://host), and RFC-generic URLs. Requires an explicit url_standard ("rfc3986" or "whatwg"), which decides the interpretation; general with url_standard = NULL is an error. Non-special / opaque hosts receive no www-stripping, no domain/TLD derivation, and are never run through the IDNA/punycode helpers. A non-special scheme with no // is an opaque path: it has no authority, so host, user, port and the domain/tld columns are all NA and the entire remainder is the path (query/fragment are still split off). This includes mailto: — the recipient's @ never re-triggers authority parsing. To decompose a mailto: recipient, use the accessors (get_host() / get_domain() / get_user(), ADR 0012 D7) or get_mailto_recipients(); those deliberately return a recipient's parts where this table presents NA, because a recipient domain is extraction metadata, not the URL's authority.

url_standard

Optional top-level standard profile: NULL (default), "rfc3986", or "whatwg". With NULL the behavior is exactly what the individual low-level options select (fully backward compatible). When set, it selects a coherent set of standard-conformant behaviors for the axes it governs — path percent/dot handling, the host IPv4/reg-name model, and case_handling — so callers do not have to hand-assemble the low-level knobs. Passing a governed low-level knob (path_normalization or case_handling) with a value the selected profile would not choose is an error; passing the value the profile would pick is accepted (only case_handling = "lower_host" is accepted under a selector — "keep", "lower", and "upper" all conflict, since "lower" also lowercases the path, which neither standard sanctions). Added as the last argument so existing positional calls keep their meaning; always pass it by name. Under "whatwg" the selector additionally recognizes a literal backslash as a path separator for WHATWG-special schemes (http/https/ftp) and nulls default ports in parse output; use port_handling = "strip_default" for spec-style clean URL port rendering. See resolve_url for url_standard-governed reference resolution. The selector does not govern whether port_handling may be set (it is a standalone editorial knob), nor does it govern path_encoding (an orthogonal path-presentation knob that layers on any profile), IDNA rendering, or query handling.

engine

Optional pslr engine controlling which Public Suffix List backs domain / TLD / subdomain extraction: NULL (default) resolves against pslr's session-global default list — exactly the historical behavior — while a pslr::psl_engine() snapshot resolves against that specific list, per request, without mutating any global state (never call pslr::psl_use() for this). Use it to pin a particular list version or to load an alternate list via pslr::psl_engine(source = "path", path = ...). Process-local: an engine holds a C++ external pointer that does not serialize across R sessions or parallel workers — build it in the process that uses it; never cache it to disk or send it to a worker (rebuild one per process instead). Only the domain-derived outputs (domain, tld, and the subdomain-trimmed host / clean_url) depend on it.

Value

A character vector of URL hosts.

Details

Under scheme_acceptance = "general" a mailto: URL's first recipient domain is returned, decomposed through the same PSL seam a web host uses, so get_domain / get_tld / get_subdomain work on it too (ADR 0012 D7). This deliberately diverges from safe_parse_url, whose host column is NA for a mailto: URL: a mailto: is a WHATWG opaque path and has no authority, so the recipient domain is surfaced here as extraction metadata rather than presented as a parsed authority. Under the default "web" acceptance a mailto: URL is not parsed and this returns NA.

Examples

get_host("http://sub.example.com:8080")
#> [1] "sub.example.com"
get_host(
  "http://www.two.one.example.com",
  subdomain_levels_to_keep = 1
) # Result: "www.one.example.com"
#> [1] "www.one.example.com"
get_host(
  "http://www.two.one.example.com",
  www_handling = "strip",
  subdomain_levels_to_keep = 1
) # Result: "one.example.com"
#> [1] "one.example.com"
get_host(
  "http://www.two.one.example.com",
  www_handling = "keep",
  subdomain_levels_to_keep = 1
) # Result: "www.one.example.com"
#> [1] "www.one.example.com"
get_host(
  "http://three.two.one.example.com",
  subdomain_levels_to_keep = 0
) # Result: "example.com"
#> [1] "example.com"
get_host(
  "http://www.three.two.one.example.com",
  subdomain_levels_to_keep = 0
) # Result: "www.example.com"
#> [1] "www.example.com"