fix: dev: improve compatibility outside of VPS layouts

bin/vps

@@ -688,11 +688,22 @@ export -f compose:charm:container_first
 
 compose:get_url() {
     local project_name="$1" service="$2"  data_file network ip
-    data_file="/var/lib/compose/relations/${project_name}/${service}-frontend/web-proxy/data"
-    if [ -e "$data_file" ]; then
+    data_dir=("/var/lib/compose/relations/${project_name}/${service}-"*"/web-proxy")
+    if [ "${#data_dir[@]}" -gt 1 ]; then
+        err "More than one web-proxy relation." \
+            "Current 'vps' algorithm is insufficient" \
+            "to figure out which relation is concerned"
+        return 1
+    fi
+    data_file="${data_dir[0]}/data"
+    if [ -d "${data_file%/*}" ]; then
         (
             set -o pipefail
-            cat "$data_file" | shyaml get-value url
+            ## users can't cat directly the content
+            docker run --rm \
+                   -v "${data_file%/*}":/tmp/dummy alpine \
+                   cat "/tmp/dummy/${data_file##*/}" |
+                shyaml get-value url
         )
     else
         ## Assume there are no frontend relation here, the url is direct IP