MINOR: lua: Allow reading "proc." scoped vars from LUA core.

This adds the "core.get_var()" method allow the reading
of "proc." scoped variables outside of TXN or HTTP/TCPApplet.

Fixes: #2212
Signed-off-by: Daan van Gorkum <djvg@djvg.net>

doc/lua-api/index.rst

@@ -381,6 +381,16 @@ Core class
 
   :returns: an array of values.
 
+.. js:function:: core.get_var()
+
+  **context**: body, init, task, action, sample-fetch, converter
+
+  Returns data stored in the variable <var> converter in Lua type.
+  This is limited to "proc." scoped variables.
+
+  :param string var: The variable name in "proc." scope according with the
+  HAProxy variable syntax.
+
 .. js:function:: core.now()
 
   **context**: body, init, task, action

src/hlua.c

@@ -1965,6 +1965,33 @@ static int hlua_set_map(lua_State *L)
 	return 0;
 }
 
+/* This function is an LUA binding. It provides a function
+ * for retrieving a var from the proc scope in core.
+ */
+ static int hlua_core_get_var(lua_State *L)
+{
+	const char *name;
+	size_t len;
+	struct sample smp;
+
+	MAY_LJMP(check_args(L, 1, "get_var"));
+
+	name = MAY_LJMP(luaL_checklstring(L, 1, &len));
+
+	/* We can only retrieve information from the proc. scope */
+	/* FIXME: I didn't want to expose vars_hash_name from vars.c */
+	if (len < 5 || strncmp(name, "proc.", 5) != 0)
+		WILL_LJMP(luaL_error(L, "'get_var': Only 'proc.' scope allowed to be retrieved in 'core.get_var()'."));
+
+	if (!vars_get_by_name(name, len, &smp, NULL)) {
+		lua_pushnil(L);
+		return 1;
+	}
+
+	return MAY_LJMP(hlua_smp2lua(L, &smp));
+	return 1;
+}
+
 /* This function disables the sending of email through the
  * legacy email sending function which is implemented using
  * checks.
@@ -13209,6 +13236,7 @@ lua_State *hlua_init_state(int thread_num)
 	hlua_class_function(L, "del_acl", hlua_del_acl);
 	hlua_class_function(L, "set_map", hlua_set_map);
 	hlua_class_function(L, "del_map", hlua_del_map);
+	hlua_class_function(L, "get_var", hlua_core_get_var);
 	hlua_class_function(L, "tcp", hlua_socket_new);
 	hlua_class_function(L, "httpclient", hlua_httpclient_new);
 	hlua_class_function(L, "event_sub", hlua_event_global_sub);