Evaluate the Windows PAC Route for an R Download

A Windows PAC script can choose a proxy according to the destination. For a download made with R’s curl package, ask its Windows helper for that URL’s route before creating the transfer handle:

url <- "https://example.com/data.csv"
route <- curl::ie_get_proxy_for_url(url)
if (is.null(route)) route <- ""

handle <- curl::new_handle(proxy = route)
connection <- curl::curl(url, handle = handle)

Read and close connection through the application’s normal connection lifecycle. The snippet establishes the route for that curl handle; it does not configure every networking package in the R process.

The helper reads the current Windows proxy configuration. When automatic configuration is enabled, evaluation can involve downloading and running the PAC script, so lookup itself may take time. Use the real target URL rather than a convenient unrelated test site.

The helper returns NULL when no proxy is selected. The explicit empty proxy string in the example tells libcurl to make this transfer directly, instead of falling back to a proxy environment variable left in the session.

A PAC file URL is not the resulting proxy endpoint. Passing that script URL as the handle’s proxy value does not ask libcurl to evaluate the script.

This lookup returns a selected proxy, not a complete browser-equivalent failover engine for every PAC candidate. It also does not supply authentication credentials. Keep the handling local to the Windows client and curl transfer that actually need this policy.