参考地址
Socket
Socket通常翻译为套接字，它是为了方便让两台机器能互相通信的一套技术，该套技术封装好了繁琐的TCP/IP协议，向外提供出简单的API简化了通信实现的过程，其可以实现不同层面，不同应用，跨进程跨网络的通信
依据Socket提供的数据传输特性可分为如下几个大类：
- Stream socket: 提供双向、有序、可靠、非重复的数据通信。大致可以认为它封装的TCP通信协议。
- Datagram socket: 提供双向数据通信，数据不一定按顺序到达。大致可以认为它封装的是UDP通信协议。
- Sequential socket: 提供双向、有序、可靠数据通信，数据包有最大限制，并且必须把这个包完整的接受才能进行读取。
- Raw socket: 提供相对TCP/UDP而言较下层的通信协议访问，如果使用非TCP/UDP的通信协议可以使用该类型的socket。
Socket通信模型
服务端
class SocketServer implements Runnable {
@Override
public void run() {
try {
ServerSocket serverSocket = new ServerSocket(8188);
while (true) {
Socket client = serverSocket.accept(); // 阻塞等待
Log.d(TAG, "===Socket connect success===");
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
客户端
/**
* Connect ServerSocket receive msg from callback
*/
public void connectServerSocket(final SocketCallback callback, final long retryTime) {
new Thread() {
@Override
public void run() {
Socket socket = null;
while (socket == null) {
try {
socket = new Socket("localhost", 8188);
client = socket;
callback.onConnectSuccess();
} catch (IOException e) {
callback.onConnectError(e);
SystemClock.sleep(retryTime);
callback.onConnectRetry();
}
}
try {
bufferedReader = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
while (true) {
String msg = bufferedReader.readLine();
if (msg != null) {
callback.onReceive(msg);
}
}
} catch (IOException e) {
callback.onReceiveError(e);
}
}
}.start();
}
TCP keep-alive
/**
* When the keepalive option is set for a TCP socket and no data
* has been exchanged across the socket in either direction for
* <2 hours> (NOTE: the actual value is implementation dependent),
* TCP automatically sends a keepalive probe to the peer. This probe is a
* TCP segment to which the peer must respond.
* One of three responses is expected:
* 1. The peer responds with the expected ACK. The application is not
* notified (since everything is OK). TCP will send another probe
* following another 2 hours of inactivity.
* 2. The peer responds with an RST, which tells the local TCP that
* the peer host has crashed and rebooted. The socket is closed.
* 3. There is no response from the peer. The socket is closed.
*
* The purpose of this option is to detect if the peer host crashes.
*
* Valid only for TCP socket: SocketImpl
*
* @see Socket#setKeepAlive
* @see Socket#getKeepAlive
*/
@Native public final static int SO_KEEPALIVE = 0x0008;
/**
* Enable/disable {@link SocketOptions#SO_KEEPALIVE SO_KEEPALIVE}.
*
* @param on whether or not to have socket keep alive turned on.
* @exception SocketException if there is an error
* in the underlying protocol, such as a TCP error.
* @since 1.3
* @see #getKeepAlive()
*/
public void setKeepAlive(boolean on) throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
getImpl().setOption(SocketOptions.SO_KEEPALIVE, Boolean.valueOf(on));
}
LocalSocket
Android中的LocalSocket是基于UNIX-domain Socket的，UNIX-domain Socket是在Socket的基础上衍生出来的一种IPC通信机制，因此LocalSocket解决的是同一台主机上不同进程间互相通信的问题。 其相对于网络通信使用的socket不需要经过网络协议栈，不需要打包拆包、计算校验，自然的执行效率也高。与大名鼎鼎的binder机制作用一样，都在Android系统中作为IPC通信手段被广泛使用。
服务端
/**
* Creates a new server socket listening at specified name.
* On the Android platform, the name is created in the Linux
* abstract namespace (instead of on the filesystem).
*
* @param name address for socket
* @throws IOException
*/
public LocalServerSocket(String name) throws IOException
{
impl = new LocalSocketImpl();
impl.create(LocalSocket.SOCKET_STREAM);
localAddress = new LocalSocketAddress(name);
impl.bind(localAddress);
impl.listen(LISTEN_BACKLOG);
}
// 如上构造方法同时处理了bind和listen
LocalServerSocket serverSock = new LocalServerSocket("com.android.bluetooth.tests.sock");
LocalSocket acceptSock = serverSock.accept();
// 获取客户端的身份以便做权限控制
Credentials credentials = acceptSock.getPeerCredentials();
Log.d(TAG, "connect success: " + pm.getNameForUid(credentials.getUid()));
客户端
LocalSocket client = new LocalSocket();
LocalSocketAddress address = new LocalSocketAddress(SOCKET_NAME, LocalSocketAddress.Namespace.ABSTRACT);
client.connect(address);
selinux
type=1400 audit(0.0:113): avc: denied { connectto } for path=0073756E6D696F70656E736572766963652E6C6F67636174 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:system_app:s0 tclass=unix_stream_socket permissive=0
allow untrusted_app system_app:unix_stream_socket connectto;
调试命令
netstat
V2:/ # netstat -h
usage: netstat [-pWrxwutneal]
Display networking information.
-r Display routing table.
-a Display all sockets (Default: Connected).
-l Display listening server sockets.
-t Display TCP sockets.
-u Display UDP sockets.
-w Display Raw sockets.
-x Display Unix sockets.
-e Display other/more information.
-n Don't resolve names.
-W Wide Display.
-p Display PID/Program name for sockets.
netstat -apn
V2:/ # netstat -apn
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program Name
tcp 0 0 127.0.0.1:5037 0.0.0.0:* LISTEN 5283/adbd
tcp 0 0 :::8080 :::* LISTEN 23636/cn.showmac.vsimservice
tcp 0 0 :::8188 :::* LISTEN 19452/com.sunmi.sunmiopenservice
tcp 0 0 ::ffff:127.0.0.1:40954 ::ffff:127.0.0.1:8188 ESTABLISHED 19535/com.sunmi.sunmiserverdemo
tcp 0 0 ::ffff:127.0.0.1:8188 ::ffff:127.0.0.1:40954 ESTABLISHED 19452/com.sunmi.sunmiopenservice
tcp 0 0 ::ffff:10.10.163.131:34 ::ffff:175.25.50.78:701 ESTABLISHED 23636/cn.showmac.vsimservice
udp 2816 0 10.10.163.131:68 10.10.175.254:67 ESTABLISHED 899/system_server
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags Type State I-Node PID/Program Name Path
unix 2 [ ACC ] STREAM LISTENING 11648428 19535/com.sunmi.sunmiserverdemo @com.sunmi.sunmiserverdemo
unix 3 [ ] STREAM CONNECTED 17963 303/vold /dev/socket/vold
unix 3 [ ] STREAM CONNECTED 15769 454/installd /dev/socket/installd
unix 2 [ ] DGRAM 2020915 5414/wpa_supplicant /data/misc/wifi/sockets/wlan0
unix 3 [ ] STREAM CONNECTED 1880643 5283/adbd @jdwp-control
Android中的Socket IPC
Socket通信方式也是C/S架构，比Binder简单很多。在Android系统中采用Socket通信方式的主要有：
- zygote：用于孵化进程，system_server创建进程是通过socket向zygote进程发起请求
- installd：用于安装App的守护进程，上层PackageManagerService很多实现最终都是交给它来完成
- lmkd：lowmemorykiller的守护进程，Java层的LowMemoryKiller最终都是由lmkd来完成
- adbd：这个也不用说，用于服务adb
- logcatd:这个不用说，用于服务logcat
- vold：即volume Daemon，是存储类的守护进程，用于负责如USB、Sdcard等存储设备的事件处理
Socket方式更多的用于Android framework层与native层之间的通信
installd
权限控制
/**
* Socket implementation used for android.net.LocalSocket and
* android.net.LocalServerSocket. Supports only AF_LOCAL sockets.
*/
class LocalSocketImpl {
/**
* Retrieves the credentials of this socket's peer. Only valid on
* connected sockets.
*
* @return non-null; peer credentials
* @throws IOException
*/
public Credentials getPeerCredentials() throws IOException {
return getPeerCredentials_native(fd);
}
}
/**
* A class for representing UNIX credentials passed via ancillary data
* on UNIX domain sockets. See "man 7 unix" on a desktop linux distro.
*/
public class Credentials {
/** pid of process. root peers may lie. */
private final int pid;
/** uid of process. root peers may lie. */
private final int uid;
/** gid of process. root peers may lie. */
private final int gid;
}
