html_url: Resolve URLs in attributes

In zuhtml: Parse 'HTML' with a Bundled 'Gumbo' Parser

Resolve URLs in attributes

Description

Reads a URL-valued attribute from each node and resolves it against the document's base URL with the reference-resolution algorithm of RFC 3986, section 5 (https://www.rfc-editor.org/rfc/rfc3986#section-5): dot segments are removed and relative, query-only, fragment-only and protocol-relative references are handled. Nothing is fetched.

Usage

html_url(x, attr = "href", base_url = NULL)

Arguments

x	A zuhtml_document or zuhtml_nodeset.
attr	The attribute holding the URL.
base_url	The base URL to resolve against, overriding the document's; NULL to use the document's.

Details

The base URL is base_url if given; otherwise the document's first ⁠<base href>⁠ resolved against the base_url given to html_parse(); otherwise that base_url alone.

This is RFC 3986, not the WHATWG URL Standard browsers implement: there is no IDNA processing, no percent-encoding of characters that need it, and no special handling of backslashes. Leading and trailing ASCII whitespace is removed from the attribute; a reference that still contains whitespace or a control character, or whose scheme is invalid, is malformed.

Value

A character vector as long as x: the resolved URL of each node. NA where the node lacks the attribute, the reference is malformed, or a relative reference has no absolute base URL to resolve against; and for missing nodes. The original attribute value stays available through html_attr().

See Also

Other extraction: html_forms(), html_links(), html_list(), html_table(), html_table_cells()

Examples

doc <- html_parse(
  "<a href='../img/a.png'>A</a><a href='//cdn.example.org/b'>B</a>",
  base_url = "https://example.org/docs/page.html"
)
html_url(html_elements(doc, "a"))
html_url(html_elements(doc, "a"), base_url = "http://other.test/x/")

zuhtml documentation built on Oct. 6, 2026, 5:06 p.m.