Android使用socket

背景

修改andorid framework，希望新增一个socket 与自定义的程序进行信息交互

实现代码

服务端
//LocalSocket graal_start_sock_raw = new LocalSocket(LocalSocket.SOCKET_SEQPACKET);
Process.ProcessStartResult my_spec_result = new Process.ProcessStartResult();

try {
LocalServerSocket graal_start_sock_server = new LocalServerSocket("_sock_graal");
LocalSocket graal_start_sock = graal_start_sock_server.accept();
    BufferedWriter cmd_out_stream =  new BufferedWriter(
                        new OutputStreamWriter(graal_start_sock.getOutputStream()),
                        Zygote.SOCKET_BUFFER_SIZE);
    DataInputStream cmd_in_stream = new DataInputStream(graal_start_sock.getInputStream());

//seee startViaZygote in ZygoteProcess.java
ArrayList args_for_graal = new ArrayList<>();
args_for_graal.add(“seq=” + app.startSeq);
String msgStr = args_for_graal.size() + “\n” + String.join(“\n”, args_for_graal) + “\n”;
cmd_out_stream.write(msgStr);

读取端
LocalSocket graal_start_sock = new LocalSocket();
long seq = -1;
try {
graal_start_sock.connect(
new LocalSocketAddress(“_sock_graal”,
LocalSocketAddress.Namespace.ABSTRACT));

    BufferedReader cmd_in_stream = new BufferedReader(
        new InputStreamReader(graal_start_sock.getInputStream()), 256);
    DataOutputStream cmd_out_stream = new DataOutputStream(graal_start_sock.getOutputStream());
    String[] args = readArgumentList(cmd_in_stream);
    seq = get_seq_from_args(args);

    cmd_out_stream.writeInt((int)android.os.Process.myPid());
    cmd_out_stream.flush();
} catch (IOException ex) {
    graal_start_sock = null;
    ex.printStackTrace();

    return -1;
}

问题

读取端总是报连接被拒绝，使用如下测试用例，尝试规避https://www.v2ex.com/t/738374 提到的addr size问题，仍然无法解决问题。

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#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <sys/un.h> 
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#define SOKET_NAME "@_sock_graal"
//#define SOKET_NAME "@_spec_sock_for_graal"

int connect_test() {
    char* name = SOKET_NAME;
    struct sockaddr_un addr;

    // add this variant
    int alen;

    int sock = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sock < 0) {
        perror("failed to create socket");
        return -1;
    }

    memset(&addr, 0, sizeof(addr));
    addr.sun_family = AF_UNIX;
    strncpy(addr.sun_path, SOKET_NAME, sizeof(addr.sun_path)-1);
    if (name[0] == '@') 
        addr.sun_path[0] = '\0';

    // Added this line 
    alen = offsetof(struct sockaddr_un, sun_path) + strlen(name);
    int cur_len = alen;
    for (;cur_len < 32; cur_len++)
    {
        int ret = connect(sock, (struct sockaddr *)&addr, cur_len);
        char buf[1024] = {0};
        if (ret == 0)
        {
            printf("success with %d\n", cur_len);
            read(sock, buf, 1024);
            return 1;
        }
        else
        {
            perror("failed to connect");
        }
        
    }
    /*
    // change sizeof(addr) to alen
    if (connect(sock, (struct sockaddr *)&addr, alen) < 0) {
        perror("failed to connect");
        close(sock);
        return -1;
    }
    */
   return 0;
}

int main()
{
    return connect_test();
}

并且使用lsof -p 查看服务端pid，可以看到确实已经成功的出现了新建的socket端口。
查看logcat，发现这里是触发了android 上的StrictMode
保护。可参考https://droidyue.com/blog/2015/09/26/android-tuning-tool-strictmode/ ，简单的说，就是在UI线程中不允许使用wait/connect这样可能会引起阻塞的操作。
由于使用C程序测试无法收到异常消息，这里只能看到连接被拒绝。

问题解决

知道问题后，可以参考frameworks/base/services/core/java/com/android/server/am/ProcessList.java的如下片段。
临时性开放权限，运行在消息循环中进行socket动作即可。

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   StrictMode.ThreadPolicy oldPolicy = StrictMode.getThreadPolicy();
   android.os.StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().permitNetwork().build());
//执行打开socket的流程。。。。
android.os.StrictMode.setThreadPolicy(oldPolicy);

参考动作

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       if ((app.info.flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0) {
    // Debuggable apps may include a wrapper script with their library directory.
    String wrapperFileName = app.info.nativeLibraryDir + "/wrap.sh";
    StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskReads();
    try {
        if (new File(wrapperFileName).exists()) {
            invokeWith = "/system/bin/logwrapper " + wrapperFileName;
        }
    } finally {
        StrictMode.setThreadPolicy(oldPolicy);
    }
}