1

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，我只能写入 64KB。之后我无法将数据写入管道。另请注意，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);
    }

}

}

当我执行这个时，我只能写 64KB。由于我每次写入使用 1KB，我得到 64 条日志，之后没有任何反应。这些管道有尺寸限制吗？有解决方法吗？感谢和问候 rtindru

4

2 回答 2

7

Linux 内核（至少是嵌入 Android 的版本）对管道有 64k 的缓冲区限制。

因此，您不能写入整个文件（大于 64k 的文件）。你要做的是

a) 创建管道

b) 创建写入器线程，它将写入此管道。它将阻塞并等待，直到阅读器线程从管道中读取内容。

c) 启动这个线程

d) 将阅读器文件描述符返回给客户端。

所以，会发生什么，作家和读者都会同时写作和阅读。写入器将在填充缓冲区时阻塞，而读取器在清空缓冲区时将阻塞。

于 2012-08-02T19:12:12.193 回答
2

我扩展了@victor-ronin's answer how into code using code from @commonsware 在回答另一个问题时：

自定义 ContentProvider - openInputStream()、openOutputStream()

于 2013-02-06T17:38:41.797 回答