add a helper function ctan_mirrors()

DESCRIPTION

@@ -22,4 +22,4 @@ License: MIT + file LICENSE
 URL: https://github.com/rstudio/tinytex
 BugReports: https://github.com/rstudio/tinytex/issues
 Encoding: UTF-8
-RoxygenNote: 7.2.3
+RoxygenNote: 7.3.1

R/install.R

@@ -27,7 +27,8 @@
 #'   \code{'http://mirrors.tuna.tsinghua.edu.cn/CTAN/'}, or
 #'   \code{'https://mirror.las.iastate.edu/tex-archive/'}. In theory, this
 #'   argument should end with the path \file{/systems/texlive/tlnet}, and if it
-#'   does not, the path will be automatically appended.
+#'   does not, the path will be automatically appended. You can get a full list
+#'   of CTAN mirrors via \code{tinytex:::ctan_mirrors()}.
 #' @param extra_packages A character vector of extra LaTeX packages to be
 #'   installed. By default, a vector of all currently installed LaTeX packages
 #'   if an existing installation of TinyTeX is found. If you want a fresh
@@ -211,6 +212,13 @@ auto_repo = function() {
   if (length(x) == 1) x else 'ctan'
 }
 
+# retrieve all CTAN (https) mirrors
+ctan_mirrors = function() {
+  x = readLines('https://ctan.org/mirrors/mirmon')
+  u = xfun::grep_sub('.*<TD ALIGN=RIGHT><A HREF="(https://[^"]+)".*', '\\1', x)
+  xfun::raw_string(u)
+}
+
 # use %APPDATA%/TinyTeX if it exists or doesn't contain spaces or non-ASCII
 # chars, otherwise use %ProgramData%, because TeX Live doesn't work when the
 # installation path contains non-ASCII chars