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/*
* Copyright 2022 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.android.libraries.mobiledatadownload.file.openers;
import android.content.Context;
import android.util.Log;
import com.google.android.libraries.mobiledatadownload.file.OpenContext;
import com.google.android.libraries.mobiledatadownload.file.Opener;
import com.google.android.libraries.mobiledatadownload.file.common.FileConvertible;
import com.google.android.libraries.mobiledatadownload.file.common.ReleasableResource;
import com.google.android.libraries.mobiledatadownload.file.openers.WriteFileOpener.FileCloser;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicInteger;
import javax.annotation.Nullable;
/**
* Opener for writing data to a {@link java.io.File} object. Depending on the backend, this may work
* one of three ways,
*
* <ol>
* <li>The simple posix path.
* <li>A /proc/self/fd/ path referring to a file descriptor for the original file.
* <li>A path to a FIFO (named pipe) to which data can be written.
* </ol>
*
* Note that the third option is disabled by default, and must be turned on with {@link
* #withFallbackToPipeUsingExecutor}.
*
* <p>Usage: <code>
* try (WriteFileOpener.FileCloser closer =
* storage.open(
* uri, WriteFileOpener.create().withFallbackToPipeUsingExecutor(executor, context))) {
* // Write to closer.file()
* }
* </code>
*/
public final class WriteFileOpener implements Opener<FileCloser> {
private static final String TAG = "WriteFileOpener";
private static final int STREAM_BUFFER_SIZE = 4096;
private static final AtomicInteger FIFO_COUNTER = new AtomicInteger();
/** A file, closeable pair. */
public interface FileCloser extends Closeable {
File file();
}
/** A FileCloser that contains a stream. */
private static class StreamFileCloser implements FileCloser {
private final File file;
private final OutputStream stream;
StreamFileCloser(File file, OutputStream stream) {
this.file = file;
this.stream = stream;
}
@Override
public File file() {
return file;
}
@Override
public void close() throws IOException {
stream.close();
}
}
/** A FileCloser that contains a named pipe and a future to the thread pumping data through it. */
private static class PipeFileCloser implements FileCloser {
private final File fifo;
private final Future<Throwable> pumpFuture;
PipeFileCloser(File fifo, Future<Throwable> pumpFuture) {
this.fifo = fifo;
this.pumpFuture = pumpFuture;
}
@Override
public File file() {
return fifo;
}
/**
* Closes the wrapped file and any associated system resources. This method will block on system
* IO if the file is piped and there is remaining data to be written to the stream.
*
* @throws IOException
*/
@Override
public void close() throws IOException {
// If the pipe's write-side was never opened, open it in order to unblock the pump thread.
// Otherwise, this is harmless to the existing stream.
try (FileOutputStream unused = new FileOutputStream(fifo)) {
// Do nothing.
} catch (IOException e) {
Log.w(TAG, "close() threw exception when trying to unblock pump", e);
} finally {
fifo.delete();
}
Pipes.getAndPropagateAsIOException(pumpFuture);
}
}
@Nullable private ExecutorService executor;
@Nullable private Context context;
private WriteFileOpener() {}
public static WriteFileOpener create() {
return new WriteFileOpener();
}
/**
* If enabled, still try to return a raw file path but, if that fails, return a FIFO (aka named
* pipe) to which the data can be written as a stream. Raw file paths are not available if there
* are any transforms installed; if there are any monitors installed; or if the backend lacks such
* support.
*
* <p>The caller MUST close the returned closeable in order to avoid a possible thread leak.
*
* <p>WARNING: FIFOs require SDK level 21+ (Lollipop). If the raw file path is unavailable and the
* current SDK level is insufficient for FIFOs, the fallback will fail (throw IOException).
*
* @param executor Executor that pumps data.
* @param context Android context for the root directory where fifos are stored.
* @return This opener.
*/
@CanIgnoreReturnValue
public WriteFileOpener withFallbackToPipeUsingExecutor(
ExecutorService executor, Context context) {
this.executor = executor;
this.context = context;
return this;
}
@Override
public FileCloser open(OpenContext openContext) throws IOException {
try (ReleasableResource<OutputStream> out =
ReleasableResource.create(WriteStreamOpener.create().open(openContext))) {
if (out.get() instanceof FileConvertible) {
File file = ((FileConvertible) out.get()).toFile();
return new StreamFileCloser(file, out.release());
}
if (executor != null) {
return pipeFromFile(out.release());
}
throw new IOException("Not convertible and fallback to pipe is disabled.");
}
}
private FileCloser pipeFromFile(OutputStream out) throws IOException {
File fifo = Pipes.makeFifo(context.getCacheDir(), TAG, FIFO_COUNTER);
Future<Throwable> future =
executor.submit(
() -> {
try (FileInputStream in = new FileInputStream(fifo)) {
// In order to reach this point, writer must have opened the FIFO, so it's ok
// to delete it.
fifo.delete();
byte[] tmp = new byte[STREAM_BUFFER_SIZE];
try {
int len;
while ((len = in.read(tmp)) != -1) {
out.write(tmp, 0, len);
}
out.flush();
} finally {
out.close();
}
} catch (IOException e) {
Log.w(TAG, "pump", e);
return e;
} catch (Throwable t) {
Log.e(TAG, "pump", t);
return t;
}
return null;
});
return new PipeFileCloser(fifo, future);
}
}
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