public function call($functionname, $functionargs, $rawpost = false, $contenttype = false) {
        $functions = $this->get_api_functions();
        $supportedmethods = [ 'get', 'put', 'post', 'patch', 'head', 'delete' ];
        if (empty($functions[$functionname])) {
            throw new coding_exception('unsupported api functionname: ' . $functionname);
        }

        $method = $functions[$functionname]['method'];
        $endpoint = $functions[$functionname]['endpoint'];

        $responsetype = $functions[$functionname]['response'];
        if (!in_array($method, $supportedmethods)) {
            throw new coding_exception('unsupported api method: ' . $method);
        }

        $args = $functions[$functionname]['args'];
        $callargs = [];
        foreach ($args as $argname => $argtype) {
            if (isset($functionargs[$argname])) {
                $callargs[$argname] = clean_param($functionargs[$argname], $argtype);
            }
        }

        // Allow params in the URL path like /me/{parent}/children.
        foreach ($callargs as $argname => $value) {
            $newendpoint = str_replace('{' . $argname . '}', $value, $endpoint);
            if ($newendpoint != $endpoint) {
                $endpoint = $newendpoint;
                unset($callargs[$argname]);
            }
        }

        if ($rawpost !== false) {
            $queryparams = $this->curl->build_post_data($callargs);
            if (!empty($queryparams)) {
                $endpoint .= '?' . $queryparams;
            }
            $callargs = $rawpost;
        }

        if (empty($contenttype)) {
            $this->curl->setHeader('Content-type: application/json');
        } else {
            $this->curl->setHeader('Content-type: ' . $contenttype);
        }
        $response = $this->curl->$method($endpoint, $callargs);

        if ($this->curl->errno == 0) {
            if ($responsetype == 'json') {
                $json = json_decode($response);

                if (!empty($json->error)) {
                    throw new rest_exception($json->error->code . ': ' . $json->error->message);
                }
                return $json;
            } else if ($responsetype == 'headers') {
                $response = $this->curl->get_raw_response();
            }
            return $response;
        } else {
            throw new rest_exception($this->curl->error, $this->curl->errno);
        }
    }