The CRAN submission checks run by
R CMD check --as-cran check
the availability of URLs in files including DESCRIPTION,
CITATION, NEWS.Rd, the .Rd help pages and HTML
files in inst/doc, plus NEWS.md and README.md in
R-devel (3.3.0-to-be). These notes explain the checks.
They are only done if the build of R in use supports a suitably recent
libcurl. Most should, but OS X ‘Snow Leopard’ and
Linux distributions from before 2013 will be too old to do so.
\urlmarkup should only be used for always-active URLs. Examples of the use of e.g.
curl -I -Lon the command line (where
curlis available). They may give different results from accessing the URL in your browser. Possible reasons include:
405status value, and such sites are not reported in the checks. But some are mis-configured, notably ‘http://www.sciencedirect.com’ (which is special-cased in the checks).
libcurlwas compiled to use: on most systems these are from the OS (by default on Windows those shipped with the
libcurlbinaries are used). Browsers may use the OS versions, or may use their own copies which can explain discrepancies.
503may work in a browser, although most do not. This has even been seen for status code
If you find one of the exceptions, explain your findings in the submission.
curlGetHeaders("http://www.mywebsite.org/"). Where redirection is permanent you should use the redirected URL.
One common issue is the redirection of
http:// URLs to
https:// URLs, or even vice versa.