我们可以对 REST 服务进行 UDP 调用吗

Question

I have a REST endpoint and I want to access it using UDP for example Java Datagram. I know its not a best practice to try even but my recent project I have some hardware limitations. Hardware can make UDP calls only and my existing services are over REST ie HTTP/HTTPS.
I am looking for any way I can reuse my existing services. I have tried following code but received UnknownHostException .

public class UDPClinet {
    public static void main(String[] args) {
        String hostname = "https://jsonplaceholder.typicode.com/posts/1";
        int port = 80;
        try {
            InetAddress address = InetAddress.getByName(hostname);
            DatagramSocket socket = new DatagramSocket();
            while (true) {
                DatagramPacket request = new DatagramPacket(new byte[1], 1, address, port);
                socket.send(request);
                byte[] buffer = new byte[512];
                DatagramPacket response = new DatagramPacket(buffer, buffer.length);
                socket.receive(response);
                String quote = new String(buffer, 0, response.getLength());
                System.out.println(quote);
                System.out.println();
                Thread.sleep(10000);
            }
        } catch (SocketTimeoutException ex) {
            System.out.println("Timeout error: " + ex.getMessage());
            ex.printStackTrace();
        } catch (IOException ex) {
            System.out.println("Client error: " + ex.getMessage());
            ex.printStackTrace();
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
    }
}

Answer 1

Is it possible to implement a RESTful service that can be called via UDP.

Yes. (See below)

Can you call your existing RESTful service via UDP?

Probably no. And certainly not without a lot of work.

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Typical RESTful services are in fact implemented using HTTP or HTTPS over TCP/IP connections. It is not possible to talk directly to an TCP-based service using UDP. The IP-level packets will have the wrong protocol family and the service's OS won't route them to the service.

However, it is possible (technically speaking) to implement RESTful services over any transport that is capable of sending messages. REST principles are agnostic of the transport protocol.

The problem will be finding a service framework that support RESTful UDP and (conventional) RESTful HTTP at the same time .

There are a couple of other practical problems:

• UDP is unreliable, and this is exacerbated if you send datagrams that won't fit into a packet with the default MTU (1500 bytes). So if you want to implement a RESTful service over UDP, you will need to play close attention to the size of request and response payloads.

• HTTPS uses TLS so that the client is able to validate the server's authenticity and then send data encrypted. TLS over UDP is possible (it is calledDTLS ) and supported by JCSE, but using it in a typical RESTful / HTTP framework may be challenging.

If you want to pursue this, look for a RESTful framework that implements CoAP (Constrained Application Protocol - RFC 7252) and DTLS.

Answer 2

You may have a look at available CoAP implementations, see coap.technology for an overview. Though I'm a committer of Eclipse/Californium , a CoAP/DTLS implementation in java, I would recommend to try that out.

CoAP also defines Cross Proxies to HTTP. There is one example available in the google cloud tutorials . It's using a older Californium version as base. Californium itself has an update proxy exmaple (but not out of the box usable for the google cloud), see Californium - Proxy2 .

Answer 3

Yes, there's a internet standard now for REST over UDP, it's goes by the name the Constrained Application Protocoal - CoAP . CoApp is defined in a series of internet standards starting with RFC 7252 .

CoAP addresses concerns raised in earlier answers to this question, including using retransmissions over UDP to make it reliable, and providing for security using DTLS.

CoAP has been designed to work on microcontrollers with as low as 10 KiB of RAM and 100 KiB of code space ( RFC 7228 ). Furthermore it adds very little overhead to the UDP packets, using a binary fixed header of 4 bytes, and variable length options (like optional HTTP headers)