我在QA的Google Pixel with Android 7.1.1(N_MR1)上遇到了一个非常奇怪的问题.
我们在建立TCP连接期间使用UDP服务器和客户端进行握手.
QA报告对Pixel的握手不起作用.在探索Logcat后,我发现UdpServerTask抛出异常：
java.net.BindException: Address already in use
at java.net.PlainDatagramSocketImpl.bind0(Native Method)
at java.net.AbstractPlainDatagramSocketImpl.bind(AbstractPlainDatagramSocketImpl.java:96)
at java.net.DatagramSocket.bind(DatagramSocket.java:387)
到目前为止我尝试了什么：
>启用重用地址功能(见代码) – 没有运气
>强制使用IPv4(见代码) – 同样,没有运气
>在循环中,检查端口范围(32100 – 32110) – 也没有帮助.此外,所有端口都抛出相同的异常java.net.BindException：地址已在使用中
>硬编码IP的“0.0.0.0”和“10.1.x.x”(见代码) – 相同
>重启设备,改变了WiFi网络 – 也没有帮助
此外,我检查了谁在设备上使用端口(NetStat应用程序) – IP和端口是免费的,没有人使用过.但是当我试图调用bind()时 – 发生异常.
同时UDP客户端(按需调用)工作正常 – 我可以通过目标端口发送UDP数据包.
另外注意到 – 在我的带有Android 7.1.1的Nexus和具有较低Android版本的设备上我无法重现这个问题.
测试示例
public class UDPServer {
int PORT = 32100;
long TIMEOUT = 30000;
private void log(String msg) {
System.out.println(msg);
}
private boolean isActive = false;
public ArrayList<UdpServerTask> tasks = new ArrayList<>();
public void process(final byte[] data) {
AsyncTask<Void, Void, Void> loadTask = new AsyncTask<Void, Void, Void>() {
@Override
protected Void doInBackground(Void... params) {
//process data
return null;
}
};
Utils.executeTask(loadTask);
}
public void startAddress(String host) {
UdpServerTask loadTask = new UdpServerTask(host, PORT);
tasks.add(loadTask);
Utils.executeTask(loadTask);
}
public void runUdpServer() {
java.lang.System.setProperty("java.net.preferIPv6Addresses", "false");
java.lang.System.setProperty("java.net.preferIPv4Stack", "true");
stop_UDP_Server();
isActive = true;
AsyncTask<Void, Void, Void> mainTask = new AsyncTask<Void, Void, Void>() {
ArrayList<String> ips = new ArrayList<>();
@Override
protected Void doInBackground(Void... params) {
log("UDP starting servers ");
ips.add(null);
ips.add("0.0.0.0");
try {
Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
while (interfaces.hasMoreElements()) {
NetworkInterface networkInterface = interfaces.nextElement();
if (networkInterface.isLoopback() || !networkInterface.isUp()) {
continue;
}
for (InterfaceAddress interfaceAddress : networkInterface.getInterfaceAddresses()) {
InetAddress broadcast = interfaceAddress
.getBroadcast();
if (broadcast == null || broadcast instanceof Inet6Address) {
continue;
}
if (!ips.contains(broadcast.getHostAddress())) {
ips.add(broadcast.getHostAddress());
}
}
}
} catch (final Throwable e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
for (String host : ips) {
startAddress(host);
}
}
};
Utils.executeTask(mainTask);
}
public boolean reallyStopped() {
return !isActive && tasks.isEmpty();
}
public void stop_UDP_Server() {
isActive = false;
AsyncTask<Void, Void, Void> mainTask = new AsyncTask<Void, Void, Void>() {
@Override
protected Void doInBackground(Void... params) {
log("UDP start stopping");
for (UdpServerTask task : tasks) {
task.cancelServer();
}
tasks.clear();
return null;
}
};
Utils.executeTask(mainTask);
while (!reallyStopped()) {
try {
Thread.sleep(100);
} catch (Exception e) {
}
}
}
private class UdpServerTask extends AsyncTask<Void, Void, Void> {
String ip;
int port;
public UdpServerTask(String ip, int port) {
this.ip = ip;
this.port = port;
}
DatagramSocket ds = null;
public void cancelServer() {
log("UDP server cancelServer");
if (ds != null && !ds.isClosed()) {
try {
ds.close();
ds = null;
} catch (Exception e) {
e.printStackTrace();
}
}
log("UDP server stopped");
}
@Override
protected Void doInBackground(Void... params) {
long time = System.currentTimeMillis();
boolean firstAttempt = true;
while (System.currentTimeMillis() - time <= TIMEOUT && isActive) {
try {
if (ds != null && !ds.isClosed()) {
try {
ds.close();
ds = null;
} catch (Exception e) {
e.printStackTrace();
}
}
log("UDP try create connection " + this.ip + ":" + this.port);
if (firstAttempt) {
ds = new DatagramSocket(new InetSocketAddress(TextUtils.isEmpty(this.ip) ? null : InetAddress.getByName(this.ip), this.port));
} else {
ds = new DatagramSocket(null);
}
ds.setBroadcast(true);
if (!firstAttempt) {
ds.setReuseAddress(true);
ds.bind(new InetSocketAddress(TextUtils.isEmpty(this.ip) ? null : InetAddress.getByName(this.ip), this.port));
}
long start = System.currentTimeMillis();
while (!ds.isBound()) {
if (System.currentTimeMillis() - start >= TIMEOUT) {
throw new Exception("Cann't bind to " + this.ip + ":" + this.port);
}
Thread.sleep(150);
}
log("UDP Server Started on " + this.ip + ":" + this.port);
while (isActive) {
final byte[] lMsg = new byte[4096];
final DatagramPacket dp = new DatagramPacket(lMsg, lMsg.length);
ds.receive(dp);
log("process UDP from " + dp.getAddress().toString() + ":" + dp.getPort());
process(dp.getData());
}
log("UDP Server Stopped on " + this.ip + ":" + this.port);
} catch (final Throwable e) {
e.printStackTrace();
firstAttempt = false;
log("UDP Server Failed " + this.ip + ":" + this.port + " " + e);
try {
Thread.sleep(TIMEOUT / 10);
} catch (Exception ex) {
}
}
}
if (ds != null && !ds.isClosed())
try {
ds.close();
ds = null;
} catch (Exception e) {
e.printStackTrace();
}
log("UDP Server finish task");
return null;
}
}
}
最佳答案 问题出在您使用的端口中.在我的Pixel手机上,/ proc / sys / net / ipv4 / ip_local_reserved_ports文件中定义了以下端口范围：
32100-32600,40100-40150
如果我将代码中的端口号更改为超出此范围的任何内容(当然,大于1024),它可以正常工作,并且我可以从其他主机向应用程序发送数据.
Linux Kernel documentation描述了这样的文件：
ip_local_reserved_ports– list of comma separated rangesSpecify the ports which are reserved for known third-party applications. These
ports will not be used by automatic port assignments (e.g. when
callingconnect()orbind()with port number 0). Explicit port
allocation behavior is unchanged.
因此,当您明确地将端口号传递给bind方法时,仍应该使用这些端口.显然这不起作用.在我看来,Android中使用的Linux内核实现提供的网络堆栈中存在一个错误.但这需要进一步调查.
您还可以在不同的手机上找到以下有用的ip_local_reserved_ports内容列表：
https://census.tsyrklevich.net/sysctls/net.ipv4.ip_local_reserved_ports
