Get all subdomain operations processed in a given transaction.
        Returns the list of subdomains on success (can be empty)
        Returns 502 on failure to get subdomains

def GET_subdomain_ops(self, path_info, txid):
        """
        Get all subdomain operations processed in a given transaction.
        Returns the list of subdomains on success (can be empty)
        Returns 502 on failure to get subdomains
        """
        blockstackd_url = get_blockstackd_url()
        subdomain_ops = None
        try:
            subdomain_ops = blockstackd_client.get_subdomain_ops_at_txid(txid, hostport=blockstackd_url)
        except ValueError:
            return self._reply_json({'error': 'Invalid argument: not a well-formed txid'}, status_code=400)

        if json_is_error(subdomain_ops):
            log.error('Failed to get subdomain operations at {}: {}'.format(txid, subdomain_ops['error']))
            return self._reply_json({'error': 'Failed to get subdomain operations'}, status_code=subdomain_ops.get('http_status', 500))

        return self._reply_json(subdomain_ops)