如何在android上实现类似“Printer Discover”的服务发现？

Question

我想了解 android 支持的“服务发现”机制 - 特别是打印机发现。

android 提供这样的发现选项吗？示例：支持 snmp 广播？

我尝试了一个应用程序“PrinterShare”链接：http://www.printeranywhere.com/mobile.sdf，其中打印机发现是通过 ipp 实现的。

如有任何帮助，我们将不胜感激。

Answer 1

Roy，我遇到了和你一样的问题，甚至在实际设备上运行该代码片段时也得到了相同的行为（独立运行代码时，而不是在 Android 中，工作得很好）。我找到了此页面并让它工作，尽管仅在设备上，通过使用以下内容来找出广播IP（而不是239.255.255.250）：

InetAddress getBroadcastAddress() throws IOException {
    WifiManager wifi = mContext.getSystemService(Context.WIFI_SERVICE);
    DhcpInfo dhcp = wifi.getDhcpInfo();
    // handle null somehow

    int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
    byte[] quads = new byte[4];
    for (int k = 0; k < 4; k++)
        quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
    return InetAddress.getByAddress(quads);
}

希望有帮助:)

Answer 2

android提供这样的发现选项吗？

据我所知，抱歉。

Answer 3

此代码片段在 J2SE 上运行良好。但是，在 Android 模拟器上，我收到响应 = 'null' 的“超时异常”

`DatagramSocket clientSocket = new DatagramSocket(8888); clientSocket.setSoTimeout(20000);

/**
 * SSDP is a text-based protocol based on the Hypertext Transfer Protocol (RFC 2616). 
 * However, it uses the User Datagram Protocol (UDP) as underlying transport protocol.
 *  Services are announced by the hosting system with multicast addressing to a 
 *  specifically designated IP multicast address at port number 1900. In IPv4, 
 *  the multicast address is 239.255.255.250.
 */
                        //getByName(host)   //host  the hostName to be resolved to an address or null.
InetAddress group = InetAddress.getByName("239.255.255.250");

//host can be null which means that an address of the loopback interface is returned.
if(group == null){
    Log.d("Discovery","getByName(): returns address of loopback interface.");
}
byte[] sendData;
byte[] receiveData = new byte[128];

String sentence = "M-SEARCH * HTTP/1.1\r\n"
    + "HOST: 239.255.255.250:1900\r\n"
    + "MAN: \"ssdp:discover\"\r\n"
    + "MX: 10\r\n"
    + "ST: ssdp:all\r\n"
    + "\r\n";

sendData = sentence.getBytes();
//public DatagramPacket (byte[] data, int length, InetAddress host, int port) 
DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, group, 1900);

try {
    clientSocket.send(sendPacket);
} catch (Exception e) {
    e.getMessage();
    e.printStackTrace();
}
Log.d("Discovery","sent packet...");
while( true)
{
    DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
    try
    {
        boolean isc = clientSocket.isConnected();
        clientSocket.receive(receivePacket);
    }
    catch ( Exception Ex)
    {
        Log.d("Discovery","Time out Exception");
    }
    if (receivePacket.getAddress() == null)
    {
        Log.d("Discovery","receivePacket.getAddress() == null");
        break;
    }
    Log.d("Discovery","Senders Address : " + receivePacket.getAddress().getHostAddress());
    String controllerResponse = new String(receivePacket.getData());       
} //end of while()
clientSocket.close(); `

Answer 4

对于 .NET 中 SSDP 的评估，此库可能很有用

https://yortw.github.io/RSSDP/