Question

我有一个使用ContentProvider类的应用。在openFile方法中，我需要能够解码文件＆amp;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，在数据完全解码之前我无法读取。写入管道。

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);
    }

}

}

当我执行此操作时，我只能写64KB。由于每次写入使用1KB，因此我得到64个日志，之后没有任何反应。这些管道有尺寸限制吗？有解决方法吗？谢谢＆amp;问候 rtindru

Answer 1

Linux内核（至少是Android中的版本）对管道有64k缓冲区限制。

所以，你不能写整个文件（大于64k）。你要做的是

a）创建管道

b）创建写入线程，该线程将写入此管道。它将阻塞并等待读者线程从管道中读取内容。

c）开始这个帖子

d）将读者文件描述符返回给客户端。

那么，会发生什么，作家和读者都会同时写作和阅读。当它清空缓冲区时，Writer将阻塞填充缓冲区并且读取器将阻塞。

Answer 2

我扩展了@ victor-ronin的答案，如何使用@commonsware中的代码代码来回答另一个问题：

Custom ContentProvider - openInputStream(), openOutputStream()

Android：ParcelFileDescriptor“createpipe”方法64KB错误

2 个答案: