From ec9992562bec1f2b5c0275f0e59926a3b088daa2 Mon Sep 17 00:00:00 2001
From: Fran Barton <francis.barton@nhs.net>
Date: Thu, 26 Mar 2026 15:08:03 +0000
Subject: [PATCH] :broom: Refactor the imds_available routine Should close #97

---
 R/get_auth_token.R    | 79 +++++++++++++++++++++----------------------
 man/imds_available.Rd |  4 +--
 2 files changed, 41 insertions(+), 42 deletions(-)

diff --git a/R/get_auth_token.R b/R/get_auth_token.R
index 7184fd2..dda963d 100644
--- a/R/get_auth_token.R
+++ b/R/get_auth_token.R
@@ -261,57 +261,56 @@ generate_resource <- function(
 }
 
 
-#' Use a token's internal `refresh()` method to refresh it
-#'
-#' This method avoids the need to refresh by re-authenticating online. It seems
-#'  like this only works with v1 tokens. v2 tokens always seem to refresh by
-#'  re-authenticating with Azure online. But v2 tokens _ought_ to refresh
-#'  automatically and not need manual refreshing. To instead generate a
-#'  completely fresh token, pass `use_cache = FALSE` or `force_refresh = TRUE`
-#'  to [get_auth_token].
-#' @param token An Azure authentication token
-#' @returns An Azure authentication token
-#' @export
-refresh_token <- \(token) token$refresh()
-
 #' Check if Azure Instance Metadata Service (IMDS) is Available
 #'
 #' This function checks if the Azure Instance Metadata Service (IMDS) is
-#' available by attempting to make a request to the IMDS endpoint. The result is
-#' cached in an environment variable for future use, saving the need for
-#' repeated checks.
+#'  available by attempting to make a request to the IMDS endpoint. The result
+#'  is cached in an environment variable for future use, saving the need for
+#'  repeated checks.
 #'
 #' You can also set the `IMDS_AVAILABLE` environment variable manually to
-#' "TRUE" or "FALSE" to override the automatic check, which can be useful for
-#' testing or in environments where the check may not work correctly.
+#'  "TRUE" or "FALSE" to override the automatic check, which can be useful for
+#'  testing or in environments where the check may not work correctly.
 imds_available <- function() {
   available <- Sys.getenv("IMDS_AVAILABLE")
 
   if (available == "") {
-    available <- tryCatch(
-      {
-        Sys.getenv(
-          "MSI_ENDPOINT",
-          "http://169.254.169.254/metadata/identity/oauth2"
-        ) |>
-          httr2::request() |>
-          httr2::req_headers(Metadata = "true") |>
-          httr2::req_timeout(0.2) |>
-          httr2::req_perform()
-
-        TRUE
-      },
-      error = function(e) FALSE
-    )
+    possibly_ping_msi_endpoint <- purrr::possibly(ping_msi_endpoint, FALSE)
+    available <- possibly_ping_msi_endpoint()
     Sys.setenv(IMDS_AVAILABLE = available)
   }
-
-  switch(toupper(available), "TRUE" = TRUE, "FALSE" = FALSE, {
-    warning(
-      "Invalid value for IMDS_AVAILABLE environment variable: ",
-      available,
-      ". Expected 'true' or 'false'. Defaulting to FALSE."
+  if (is.na(as.logical(available))) {
+    cli::cli_alert_warning(
+      "Invalid value for IMDS_AVAILABLE environment variable: {available}.",
+      "Expected 'TRUE' or 'FALSE'. Defaulting to FALSE."
     )
     FALSE
-  })
+  } else {
+    available
+  }
 }
+
+
+ping_msi_endpoint <- function() {
+  fallback_url <- "http://169.254.169.254/metadata/identity/oauth2"
+  Sys.getenv("MSI_ENDPOINT", fallback_url) |>
+    httr2::request() |>
+    httr2::req_headers(Metadata = "true") |>
+    httr2::req_timeout(0.2) |>
+    httr2::req_perform()
+  TRUE
+}
+
+
+#' Use a token's internal `refresh()` method to refresh it
+#'
+#' This method avoids the need to refresh by re-authenticating online. It seems
+#'  like this only works with v1 tokens. v2 tokens always seem to refresh by
+#'  re-authenticating with Azure online. But v2 tokens _ought_ to refresh
+#'  automatically and not need manual refreshing. To instead generate a
+#'  completely fresh token, pass `use_cache = FALSE` or `force_refresh = TRUE`
+#'  to [get_auth_token].
+#' @param token An Azure authentication token
+#' @returns An Azure authentication token
+#' @export
+refresh_token <- \(token) token$refresh()
diff --git a/man/imds_available.Rd b/man/imds_available.Rd
index 22abcc6..53334a9 100644
--- a/man/imds_available.Rd
+++ b/man/imds_available.Rd
@@ -8,8 +8,8 @@ imds_available()
 }
 \description{
 This function checks if the Azure Instance Metadata Service (IMDS) is
-available by attempting to make a request to the IMDS endpoint. The result is
-cached in an environment variable for future use, saving the need for
+available by attempting to make a request to the IMDS endpoint. The result
+is cached in an environment variable for future use, saving the need for
 repeated checks.
 }
 \details{