使用ParcelFileDescriptor.createPipe()将InputStream传输到另一个服务(跨进程边界),并使用"EBADF(错误的文件编号)"

Question

我想通过使用ParcelFileDescriptor.createPipe()一个流到流的复制线程和一个ParcelFileDescriptor,将一个Android服务从一个Android服务"发送"到一个不同进程中运行的另一个服务,该表示管道的读取端,它被提供给另一个服务借助Binder IPC.

发送代码(流程A)

我想将一个给定的InputStream发送到接收服务:

public sendInputStream() {
    InputStream is = ...; // that's the stream for process/service B
    ParcelFileDescriptor pdf = ParcelFileDescriptorUtil.pipeFrom(is);
    inputStreamService.inputStream(pdf);
}

ParcelFileDescriptorUtil是一个帮助器类,具有经典的java.io.流到流复制线程:

public class ParcelFileDescriptorUtil {

    public static ParcelFileDescriptor pipeFrom(InputStream inputStream) throws IOException {
        ParcelFileDescriptor[] pipe = ParcelFileDescriptor.createPipe();
        ParcelFileDescriptor readSide = pipe[0];
        ParcelFileDescriptor writeSide = pipe[1];

        // start the transfer thread
        new TransferThread(inputStream, new ParcelFileDescriptor.AutoCloseOutputStream(writeSide)).start();

        return readSide;
    }

    static class TransferThread extends Thread {
        final InputStream mIn;
        final OutputStream mOut;

        TransferThread(InputStream in, OutputStream out) {
            super("ParcelFileDescriptor Transfer Thread");
            mIn = in;
            mOut = out;
            setDaemon(true);
        }

        @Override
        public void run() {
            byte[] buf = new byte[1024];
            int len;

            try {
                while ((len = mIn.read(buf)) > 0) {
                    mOut.write(buf, 0, len);
                }
                mOut.flush(); // just to be safe
            } catch (IOException e) {
                LOG.e("TransferThread", e);
            }
            finally {
                try {
                    mIn.close();
                } catch (IOException e) {
                }
                try {
                    mOut.close();
                } catch (IOException e) {
                }
            }
        }
    }
}

接收服务代码(流程B)

接收服务.aidl:

package org.exmaple;
interface IInputStreamService {
    void inputStream(in ParcelFileDescriptor pfd);
}

进程A调用的接收服务:

public class InputStreamService extends Service {

@Override
public IBinder onBind(Intent intent) {
    return mBinder;
}

private final IInputStreamService.Stub mBinder = new IInputStreamService.Stub() {

    @Override
    public void inputStream(ParcelFileDescriptor pfd) throws RemoteException {

        InputStream is = new ParcelFileDescriptor.AutoCloseInputStream(pfd);
        OutputStream os = ...;
        int len;
        byte[] buf = new byte[1024];
        try {
            while ((len = is.read(buf)) > 0) {
                os.write(buf, 0, len);
            }
        } catch (IOException e) {
                        // this catches the exception shown below
        }
    }
};

但in.read()在inputStream()始终引发IOException

java.io.IOException: read failed: EBADF (Bad file number)
    at libcore.io.IoBridge.read(IoBridge.java:442)
    at java.io.FileInputStream.read(FileInputStream.java:179)
    at java.io.InputStream.read(InputStream.java:163)

看起来EBADF错误是read()在文件描述符关闭时设置的.但我不知道是什么导致它以及如何解决它.

是的,我知道ConentProvider也是可能的.但它不应该与我的方法一起工作吗？有没有其他方法可以将InputStream流传递给Android中的其他服务？

^{在一个侧面说明:CommonsWare创造了一个类似的使用ContentProvider的项目(相关SO问题1,2).这是我从我的方法中获得大部分想法的地方}

Answer 1

似乎原因是ParcelFileDescriptor作为服务方法的参数.如果服务确实返回,ParcelFileDescriptor它按预期工作.

发送服务(流程A)

public sendInputStream() {
    InputStream is = ...; // that's the stream for process/service B
    ParcelFileDescriptor pfd = inputStreamService.inputStream();
    OutputStream os = new ParcelFileDescriptor.AutoCloseOutputStream(pfd);

    int len;
    byte[] buf = new byte[1024];
    try {
        while ((len = is.read(buf)) > 0) {
            os.write(buf, 0, len);
    } catch (IOException e) {
    } finally {
        try { is.close(); } catch (IOException e1) {}
        try { os.close(); ] catch (IOException e1) {}
    }
}

接收服务代码(流程B)

接收服务.aidl:

package org.exmaple;
interface IInputStreamService {
    ParcelFileDescriptor inputStream();
}

进程A调用的接收服务:

public class InputStreamService extends Service {

@Override
public IBinder onBind(Intent intent) {
    return mBinder;
}

private final IInputStreamService.Stub mBinder = new IInputStreamService.Stub() {

    @Override
    public void ParcelFileDescriptor inputStream() throws RemoteException {
                // one can read the contents of the Processes A's InputStream
                // from the following OutputStream
                OutputStream os = ...;
                ParcelFileDescriptor pfd = ParcelFileDescriptorUtil.pipeTo(os);
                return pfd;
    }
};

ParcelFileDescriptorUtil是一个辅助类,具有经典的java.io.流到流复制线程.现在我们必须使用该pipeTo()方法.

public class ParcelFileDescriptorUtil {

    public static ParcelFileDescriptor pipeTo(OutputStream outputStream) throws IOException {
        ParcelFileDescriptor[] pipe = ParcelFileDescriptor.createPipe();
        ParcelFileDescriptor readSide = pipe[0];
        ParcelFileDescriptor writeSide = pipe[1];

        // start the transfer thread
        new TransferThread(new ParcelFileDescriptor.AutoCloseInputStream(readSide), outputStream).start();

        return writeSide;
    }

    static class TransferThread extends Thread {
        final InputStream mIn;
        final OutputStream mOut;

        TransferThread(InputStream in, OutputStream out) {
            super("ParcelFileDescriptor Transfer Thread");
            mIn = in;
            mOut = out;
            setDaemon(true);
        }

        @Override
        public void run() {
            byte[] buf = new byte[1024];
            int len;

            try {
                while ((len = mIn.read(buf)) > 0) {
                    mOut.write(buf, 0, len);
                }
                mOut.flush(); // just to be safe
            } catch (IOException e) {
                LOG.e("TransferThread", e);
            }
            finally {
                try {
                    mIn.close();
                } catch (IOException e) {
                }
                try {
                    mOut.close();
                } catch (IOException e) {
                }
            }
        }
    }
}

这允许您跨进程边界传输InputStream,一个缺点是流到流副本中涉及一些CPU时间.