resp_link_url() doesn't handle multiple link headers

[maarten-vermeyen]

Hi everyone,

I came upon an issue with responses with multiple link headers in the response. While this is allowed by RFC 8288 (https://www.rfc-editor.org/rfc/rfc8288.html, see examples at bottom of section 3.5), the call to resp_link_url() and the underlying call to resp_header() only returns the value of the first header.

Example:

library(httr2)

# example request
resp <- request("https://geo.api.vlaanderen.be/Gebouwenregister") |>
          req_url_path_append("ogc/features/v1/collections/Gebouw/items") |>
          req_url_query(limit=50, 
                        crs="http://www.opengis.net/def/crs/EPSG/0/31370",
                        startIndex=50) |>
          req_headers(Accept = "application/geo+json") |>
          req_perform()

# headers contain multiple links
print(resp_headers(resp))

# resp_link_url() will return NULL for rel "next"
print(resp_link_url(resp, rel="next")

# resp_header("link") returns only the first value
print(resp_header(resp, "link")

Output:

<httr2_headers>
date: Fri, 22 Nov 2024 21:14:48 GMT
content-type: application/geo+json
x-ms-middleware-request-id: 00000000-0000-0000-0000-000000000000
x-content-type-options: nosniff
link: <https://geo.api.vlaanderen.be/Gebouwenregister/ogc/features/v1/collections/Gebouw/items?limit=50&crs=http%3A%2F%2Fwww.opengis.net%2Fdef%2Fcrs%2FEPSG%2F0%2F31370&startIndex=0>; rel="prev"; type="application/geo+json"
link: <https://geo.api.vlaanderen.be/Gebouwenregister/ogc/features/v1/collections/Gebouw/items?limit=50&crs=http%3A%2F%2Fwww.opengis.net%2Fdef%2Fcrs%2FEPSG%2F0%2F31370&startIndex=100>; rel="next"; type="application/geo+json"
content-crs: <http://www.opengis.net/def/crs/EPSG/0/31370>
api-version: 1.0.1
content-disposition: inline; filename=Gebouw.json
access-control-allow-origin: *
x-robots-tag: all
NULL
[1] "<https://geo.api.vlaanderen.be/Gebouwenregister/ogc/features/v1/collections/Gebouw/items?limit=50&crs=http%3A%2F%2Fwww.opengis.net%2Fdef%2Fcrs%2FEPSG%2F0%2F31370&startIndex=0>; rel=\"prev\"; type=\"application/geo+json\""

I'm not sure what would be the optimal solution for this problem. I think the easiest would be to adapt the function resp_link_url() to use resp_headers(resp, filter='link') and than handle each link header, instead of using resp_header('link').

Kind regards,

Maarten