Amp\Artax\HttpSocketPool::checkout PHP Method

    public function checkout($uri, array $options = [])
    {
        // Normalize away any IPv6 brackets -- socket resolution will handle that
        $uri = str_replace(['[', ']'], '', $uri);
        $uriParts = @parse_url($uri);
        $scheme = isset($uriParts['scheme']) ? $uriParts['scheme'] : null;
        $host = $uriParts['host'];
        $port = $uriParts['port'];
        $options = $options ? array_merge($this->options, $options) : $this->options;
        if ($scheme === 'http') {
            $proxy = $options[self::OP_PROXY_HTTP];
        } elseif ($scheme === 'https') {
            $proxy = $options[self::OP_PROXY_HTTPS];
        } else {
            return new Failure(new \DomainException('Either http:// or https:// URI scheme required for HTTP socket checkout'));
        }
        // The underlying TCP pool will ignore the URI fragment when connecting but retain it in the
        // name when tracking hostname connection counts. This allows us to expose host connection
        // limits transparently even when connecting through a proxy.
        $authority = "{$host}:{$port}";
        $uri = $proxy ? "tcp://{$proxy}#{$authority}" : "tcp://{$authority}";
        $promisor = new Deferred();
        $futureCheckout = $this->sockPool->checkout($uri, $options);
        $futureCheckout->when(function ($error, $socket) use($promisor, $proxy, $authority) {
            if ($error) {
                $promisor->fail($error);
            } elseif ($proxy) {
                $this->tunnelThroughProxy($promisor, $socket, $authority);
            } else {
                $promisor->succeed($socket);
            }
        });
        return $promisor->promise();
    }