Android: ParcelFileDescriptor "createpipe“方法64KB错误

Question

我有一个使用ContentProvider类的应用程序。在openFile方法中，我需要能够解码文件并将其作为数据流返回。所以我决定使用内置管道。

问题是，如果我使用createPipe方法，我只能向其中写入64KB。在那之后，我就无法将数据写入到管道中。还要注意，在数据完全解码并写入管道之前，我无法读取。

package com.aujas.html.viewer.content;
public class LocalFileContentProvider extends ContentProvider {

private static final String URI_PREFIX = "content://com.aujas.html.viewer.localfile.dec/";
public static File file;
public String filename;
public ParcelFileDescriptor[] parcels;

public static String constructUri(String url) {
    String editString = url.replaceAll("%20", " ");
    int n = editString.length();
    String uri = editString.substring(5, n - 1);
    Log.d("URI", uri);
    return URI_PREFIX + uri + "\"";
}

public ParcelFileDescriptor openFile(Uri uri, String mode) {

    Log.d("OPEN", uri.getPath());
    return parcels[0];

}

@Override
public boolean onCreate() {
    return true;
}

@Override
public int delete(Uri uri, String s, String[] as) {
    throw new UnsupportedOperationException(
            "Not supported by this provider");
}

@Override
public String getType(Uri uri) {
    throw new UnsupportedOperationException(
            "Not supported by this provider");
}

@Override
public Uri insert(Uri uri, ContentValues contentvalues) {
    throw new UnsupportedOperationException(
            "Not supported by this provider");
}

@Override
public Cursor query(Uri uri, String[] as, String s, String[] as1, String s1) {
    throw new UnsupportedOperationException(
            "Not supported by this provider");
}

@Override
public int update(Uri uri, ContentValues contentvalues, String s,
        String[] as) {
    throw new UnsupportedOperationException(
            "Not supported by this provider");
}

class DecryptAsync extends AsyncTask<String, Integer, String> {

    @Override
    protected String doInBackground(String... paramArrayOfParams) {
        // TODO Auto-generated method stub
        try {
            file = new File(paramArrayOfParams[0]);
            Log.d("DecrypOpened", file.toString());
            parcels = ParcelFileDescriptor.createPipe();
            Log.d("filebeindec", LocalFileContentProvider.file.toString());
            FileInputStream fis = new FileInputStream(LocalFileContentProvider.file);

            android.os.ParcelFileDescriptor.AutoCloseOutputStream out = new android.os.ParcelFileDescriptor.AutoCloseOutputStream(parcels[1]);
            Cipher ecipher;
            Cipher dcipher;
            SecretKey key;
            String input = "768f8a949de079da";
            byte[] encoded = new BigInteger(input, 16).toByteArray();
            key = new SecretKeySpec(encoded, "DES");
            byte[] iv = new byte[] { (byte) 0x8E, 0x12, 0x39, (byte) 0x9C,
                    0x07, 0x72, 0x6F, 0x5A };
            AlgorithmParameterSpec paramSpec = new IvParameterSpec(iv);
            ecipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
            dcipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
            ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
            dcipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
            byte[] buf = new byte[1024];
            InputStream in = new CipherInputStream(fis, dcipher);
            int numRead = 0;
            int n = 1;
            while ((numRead = in.read(buf)) >= 0) {
                n++;
                out.write(buf, 0, numRead);
                Log.d("Error", "SD");
                if (n == 64) {
                    out.flush();
                    out.flush();
                    n = 0;
                }
            }

            Log.d("Decypt Done", out.toString());
        } catch (Exception e) {
            Log.d("AsyncError", e.toString());
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
    }

}

}

当我执行这个命令时，我只能写64KB。因为我每次写入使用1KB，所以我会得到64个日志，之后什么都不会发生。这些管道有尺寸限制吗？有解决办法吗？感谢并问候rtindru

Answer 1

Linux内核(至少是Android中预制的版本)对管道有64k的缓冲限制。

因此，您不能写入整个文件(大于64k )。你要做的是

a)创建管道

b)创建写线程，该线程将写入该管道。它将阻塞并等待，直到读取器线程从管道读取内容。

c)启动该线程

d)向客户端返回阅读器文件描述符。

那么，将会发生什么，作者和读者将同时写作和阅读。写入器将在填充缓冲区时阻塞，而读取器将在清空缓冲区时阻塞。

Answer 2

在回答另一个问题时，我使用@commonsware中的代码将@victor-ronin的答案扩展为代码：

Custom ContentProvider - openInputStream(), openOutputStream()