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      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.documentsui.archives;
     18 
     19 import android.os.ProxyFileDescriptorCallback;
     20 import android.system.ErrnoException;
     21 import android.system.OsConstants;
     22 import android.util.Log;
     23 import android.util.jar.StrictJarFile;
     24 
     25 import java.io.IOException;
     26 import java.io.InputStream;
     27 import java.util.zip.ZipEntry;
     28 
     29 import libcore.io.IoUtils;
     30 
     31 /**
     32  * Provides a backend for a seekable file descriptors for files in archives.
     33  */
     34 public class Proxy extends ProxyFileDescriptorCallback {
     35     private final StrictJarFile mFile;
     36     private final ZipEntry mEntry;
     37     private InputStream mInputStream = null;
     38     private long mOffset = 0;
     39 
     40     Proxy(StrictJarFile file, ZipEntry entry) throws IOException {
     41         mFile = file;
     42         mEntry = entry;
     43         recreateInputStream();
     44     }
     45 
     46     @Override
     47     public long onGetSize() throws ErrnoException {
     48         return mEntry.getSize();
     49     }
     50 
     51     @Override
     52     public int onRead(long offset, int size, byte[] data) throws ErrnoException {
     53         // TODO: Add a ring buffer to prevent expensive seeks.
     54         if (offset < mOffset) {
     55             try {
     56                 recreateInputStream();
     57             } catch (IOException e) {
     58                 throw new ErrnoException("onRead", OsConstants.EIO);
     59             }
     60         }
     61 
     62         while (mOffset < offset) {
     63             try {
     64                 mOffset +=  mInputStream.skip(offset - mOffset);
     65             } catch (IOException e) {
     66                 throw new ErrnoException("onRead", OsConstants.EIO);
     67             }
     68         }
     69 
     70         int remainingSize = size;
     71         while (remainingSize > 0) {
     72             try {
     73                 int bytes = mInputStream.read(data, size - remainingSize, remainingSize);
     74                 if (bytes <= 0) {
     75                     return size - remainingSize;
     76                 }
     77                 remainingSize -= bytes;
     78                 mOffset += bytes;
     79             } catch (IOException e) {
     80                 throw new ErrnoException("onRead", OsConstants.EIO);
     81             }
     82         }
     83 
     84         return size - remainingSize;
     85    }
     86 
     87     @Override public void onRelease() {
     88         IoUtils.closeQuietly(mInputStream);
     89     }
     90 
     91     private void recreateInputStream() throws IOException {
     92         IoUtils.closeQuietly(mInputStream);
     93         mInputStream = mFile.getInputStream(mEntry);
     94         mOffset = 0;
     95     }
     96 }
     97