chg: dev: refactor out ``metadata`` reading for provide

We will need it when looking for charms provider.

bin/compose-core

@@ -1977,6 +1977,54 @@ _get_services_uses() {
 export -f _get_services_uses
 
 
+_get_provides_provides() {
+    local provides="$1" cache_file="$CACHEDIR/$FUNCNAME.cache.$(printf "%s\0" "$@" | md5_compat)" \
+          service rn rd
+
+    if [ -e "$cache_file" ]; then
+        debug "$FUNCNAME: CACHEDIR cache hit $1"
+        cat "$cache_file"
+        return 0
+    fi
+
+    type=$(printf "%s" "$provides" | shyaml get-type)
+    case "$type" in
+        sequence)
+            while read-0 prov; do
+                printf "%s\0" "$prov" ""
+            done < <(echo "$provides" | shyaml get-values-0)
+            ;;
+        struct)
+            printf "%s" "$provides" | shyaml key-values-0
+            ;;
+        str)
+            printf "%s\0" "$(echo "$provides" | shyaml get-value)" ""
+            ;;
+        *)
+            err "Unexpected type '$type' for provider identifier in charm '$charm'."
+            return 1
+    esac | tee "$cache_file"
+    return "${PIPESTATUS[0]}"
+}
+
+
+_get_metadata_provides() {
+    local metadata="$1" cache_file="$CACHEDIR/$FUNCNAME.cache.$(printf "%s\0" "$@" | md5_compat)" \
+          service rn rd
+
+    if [ -e "$cache_file" ]; then
+        debug "$FUNCNAME: CACHEDIR cache hit"
+        cat "$cache_file"
+        return 0
+    fi
+
+    provides=$(printf "%s" "$metadata" | shyaml get-value -y -q provides "")
+    [ "$provides" -a "$provides" != "''" ] || { touch "$cache_file"; return 0; }
+
+    _get_provides_provides "$provides" | tee "$cache_file"
+    return "${PIPESTATUS[0]}"
+}
+
 _get_services_provides() {
     local cache_file="$state_tmpdir/$FUNCNAME.cache.$(printf "%s\0" "$@" | md5_compat)" \
           service rn rd
@@ -1993,7 +2041,7 @@ _get_services_provides() {
 
         while read-0 rn rd; do
             printf "%s\0" "$service" "$rn" "$rd"
-        done < <(printf "%s" "$metadata" | shyaml key-values-0 provides 2>/dev/null)
+        done < <(_get_metadata_provides "$metadata")
     done > "$cache_file"
     if [ "$?" != 0 ]; then
         rm -f "$cache_file"  ## no cache