+/**
+ * Check a connection to the backend
+ * @param proxy_function calling proxy scheme (http, ajp, ...)
+ * @param conn acquired connection
+ * @param s current server record
+ * @param expect_empty whether to check for empty (no data available) or not
+ * @return APR_SUCCESS or,
+ * APR_ENOTSOCK: not connected,
+ * APR_NOTFOUND: worker in error state (unusable),
+ * APR_ENOTEMPTY: expect_empty set but the connection has data,
+ * other: connection closed/aborted (remotely)
+ */
+PROXY_DECLARE(apr_status_t) ap_proxy_check_backend(const char *proxy_function,
+ proxy_conn_rec *conn,
+ server_rec *s,
+ int expect_empty);
+