The most reliable and quick way to perform synchronous HTTP call with URLSession. See https://github.com/eonil/swift-sync-http for packaged library.

HTTP.get.swift

enum HTTP {
    /// - Note:
    ///     This does not consider HTTP status into success/failure.
    ///     Returning result can be non 2xx status.
    static func get(address:String, query: [URLQueryItem] = []) throws -> Data {
        let u = URL(string: address)!
        var reply = Data()
        /// We need to make a session object.
        /// This is key to make this work. This won't work with shared session.
        let conf = URLSessionConfiguration.ephemeral
        let sess = URLSession(configuration: conf)
        let task = sess.dataTask(with: u) { data, _, _ in
            reply = data ?? Data()
        }
        task.resume()
        while task.state != .completed {
            Thread.sleep(forTimeInterval: 0.1)
        }
        FileHandle.standardOutput.write(reply)
        if let err = task.error {
            throw err
        }
        guard let res = task.response else { return Data() }
        print(res)
        return reply
    }
}