adding more reliable miktex download

.ci/download-miktex.R

@@ -0,0 +1,25 @@
+# mirrors that host miktexsetup.zip do so only with explicitly-named
+# files like miktexsetup-2.4.5.zip, so hard-coding a link to an archive as a
+# way to peg to one mirror does not work
+#
+# this script will find the specific version of miktexsetup.zip at a given
+# mirror
+library(httr)
+args <- commandArgs(trailingOnly = TRUE)
+DESTFILE <- args[[1L]]
+MIRROR <- "https://ctan.math.illinois.edu/systems/win32/miktex/setup/windows-x64/"
+mirror_contents <- httr::content(
+    httr::RETRY("GET", mirror)
+    , as = "text"
+)
+content_lines <- strsplit(mirror_contents, "\n")[[1L]]
+content_lines <- content_lines[grepl("miktexsetup-.*", content_lines)]
+zip_loc <- regexpr(">miktexsetup-[0-9]+.*x64\\.zip", content_lines)
+zip_name <- gsub(">", "", regmatches(content_lines, zip_loc))
+full_zip_url <- file.path(MIRROR, zip_name)
+print(sprintf("downloading %s", full_zip_url))
+download.file(
+    url = full_zip_url
+    , destfile = DESTFILE
+)
+print(sprintf("MiKTeX setup downloaded to %s", DESTFILE))

.ci/test_r_package_windows.ps1

@@ -52,7 +52,8 @@ Write-Output "Done installing Rtools"
 # build the package documentation for those
 if ($env:COMPILER -eq "MINGW") {
     Write-Output "Downloading MiKTeX"
-    Download-File-With-Retries -url "https://miktex.org/download/win/miktexsetup-x64.zip" -destfile "miktexsetup-x64.zip"
+    Rscript $env:BUILD_SOURCESDIRECTORY\.ci\download-miktex.R "miktexsetup-x64.zip"
+    #Download-File-With-Retries -url "https://miktex.org/download/win/miktexsetup-x64.zip" -destfile "miktexsetup-x64.zip"
     Add-Type -AssemblyName System.IO.Compression.FileSystem
     [System.IO.Compression.ZipFile]::ExtractToDirectory("miktexsetup-x64.zip", "miktex")
     Write-Output "Setting up MiKTeX"