src/Composer/Repository/Pear/ChannelReader.php
private function selectRestVersion($channelXml, $supportedVersions)
    {
        $channelXml->registerXPathNamespace('ns', self::CHANNEL_NS);

        foreach ($supportedVersions as $version) {
            $xpathTest = "ns:servers/ns:*/ns:rest/ns:baseurl[@type='{$version}']";
            $testResult = $channelXml->xpath($xpathTest);

            foreach ($testResult as $result) {
                // Choose first https:// option.
                $result = (string) $result;
                if (preg_match('{^https://}i', $result)) {
                    return array('version' => $version, 'baseUrl' => $result);
                }
            }

            // Fallback to non-https if it does not exist.
            if (count($testResult) > 0) {
                return array('version' => $version, 'baseUrl' => (string) $testResult[0]);
            }
        }

        return null;
    }
private function selectRestVersion($channelXml, $supportedVersions)
    {
        $channelXml->registerXPathNamespace('ns', self::CHANNEL_NS);

        foreach ($supportedVersions as $version) {
            $xpathTest = "ns:servers/ns:*/ns:rest/ns:baseurl[@type='{$version}']";
            $testResult = $channelXml->xpath($xpathTest);

            foreach ($testResult as $result) {
                // Choose first https:// option.
                $result = (string) $result;
                if (preg_match('{^https://}i', $result)) {
                    return array('version' => $version, 'baseUrl' => $result);
                }
            }

            // Fallback to non-https if it does not exist.
            if (count($testResult) > 0) {
                return array('version' => $version, 'baseUrl' => (string) $testResult[0]);
            }
        }

        return null;
    }
Reads channel supported REST interfaces and selects one of them

@param \SimpleXMLElement $channelXml
@param string[] $supportedVersions supported PEAR REST protocols
@return array|null hash with selected version and baseUrl