--- /dev/null
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * 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 android.os;
+
+import android.content.Context;
+import android.os.storage.StorageManager;
+import android.system.ErrnoException;
+import android.system.Os;
+import android.system.OsConstants;
+import android.util.Slog;
+
+import libcore.io.IoUtils;
+
+import java.io.File;
+import java.io.FileDescriptor;
+import java.io.IOException;
+import java.io.InterruptedIOException;
+
+/**
+ * Variant of {@link FileDescriptor} that allows its creator to specify regions
+ * that should be redacted (appearing as zeros to the reader).
+ *
+ * @hide
+ */
+public class RedactingFileDescriptor {
+ private static final String TAG = "RedactingFileDescriptor";
+ private static final boolean DEBUG = true;
+
+ private final long[] mRedactRanges;
+
+ private FileDescriptor mInner = null;
+ private ParcelFileDescriptor mOuter = null;
+
+ private RedactingFileDescriptor(Context context, File file, long[] redactRanges)
+ throws IOException {
+ mRedactRanges = checkRangesArgument(redactRanges);
+
+ try {
+ try {
+ mInner = Os.open(file.getAbsolutePath(), OsConstants.O_RDONLY, 0);
+ mOuter = context.getSystemService(StorageManager.class)
+ .openProxyFileDescriptor(ParcelFileDescriptor.MODE_READ_ONLY, mCallback);
+ } catch (ErrnoException e) {
+ throw e.rethrowAsIOException();
+ }
+ } catch (IOException e) {
+ IoUtils.closeQuietly(mInner);
+ IoUtils.closeQuietly(mOuter);
+ throw e;
+ }
+ }
+
+ private static long[] checkRangesArgument(long[] ranges) {
+ if (ranges.length % 2 != 0) {
+ throw new IllegalArgumentException();
+ }
+ for (int i = 0; i < ranges.length - 1; i += 2) {
+ if (ranges[i] > ranges[i + 1]) {
+ throw new IllegalArgumentException();
+ }
+ }
+ return ranges;
+ }
+
+ /**
+ * Open the given {@link File} and returns a {@link ParcelFileDescriptor}
+ * that offers a redacted, read-only view of the underlying data.
+ *
+ * @param file The underlying file to open.
+ * @param redactRanges List of file offsets that should be redacted, stored
+ * as {@code [start1, end1, start2, end2, ...]}. Start values are
+ * inclusive and end values are exclusive.
+ */
+ public static ParcelFileDescriptor open(Context context, File file, long[] redactRanges)
+ throws IOException {
+ return new RedactingFileDescriptor(context, file, redactRanges).mOuter;
+ }
+
+ private final ProxyFileDescriptorCallback mCallback = new ProxyFileDescriptorCallback() {
+ @Override
+ public long onGetSize() throws ErrnoException {
+ return Os.fstat(mInner).st_size;
+ }
+
+ @Override
+ public int onRead(long offset, int size, byte[] data) throws ErrnoException {
+ int n = 0;
+ while (n < size) {
+ try {
+ final int res = Os.pread(mInner, data, n, size - n, offset + n);
+ if (res == 0) {
+ break;
+ } else {
+ n += res;
+ }
+ } catch (InterruptedIOException e) {
+ n += e.bytesTransferred;
+ }
+ }
+
+ // Redact any relevant ranges before returning
+ final long[] ranges = mRedactRanges;
+ for (int i = 0; i < ranges.length; i += 2) {
+ final long start = Math.max(offset, ranges[i]);
+ final long end = Math.min(offset + size, ranges[i + 1]);
+ for (long j = start; j < end; j++) {
+ data[(int) (j - offset)] = 0;
+ }
+ }
+ return n;
+ }
+
+ @Override
+ public int onWrite(long offset, int size, byte[] data) throws ErrnoException {
+ throw new ErrnoException(TAG, OsConstants.EBADF);
+ }
+
+ @Override
+ public void onFsync() throws ErrnoException {
+ Os.fsync(mInner);
+ }
+
+ @Override
+ public void onRelease() {
+ if (DEBUG) Slog.v(TAG, "onRelease()");
+ IoUtils.closeQuietly(mInner);
+ }
+ };
+}
--- /dev/null
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * 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 android.os;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+
+import android.content.Context;
+import android.support.test.InstrumentationRegistry;
+import android.support.test.runner.AndroidJUnit4;
+import android.system.Os;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.io.File;
+import java.io.FileDescriptor;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.util.Arrays;
+
+@RunWith(AndroidJUnit4.class)
+public class RedactingFileDescriptorTest {
+ private Context mContext;
+ private File mFile;
+
+ @Before
+ public void setUp() throws Exception {
+ mContext = InstrumentationRegistry.getContext();
+ mFile = File.createTempFile("redacting", "dat");
+ try (FileOutputStream out = new FileOutputStream(mFile)) {
+ final byte[] buf = new byte[1_000_000];
+ Arrays.fill(buf, (byte) 64);
+ out.write(buf);
+ }
+ }
+
+ @After
+ public void tearDown() throws Exception {
+ mFile.delete();
+ }
+
+ @Test
+ public void testSingleByte() throws Exception {
+ final FileDescriptor fd = RedactingFileDescriptor
+ .open(mContext, mFile, new long[] { 10, 11 }).getFileDescriptor();
+
+ final byte[] buf = new byte[1_000];
+ assertEquals(buf.length, Os.read(fd, buf, 0, buf.length));
+ for (int i = 0; i < buf.length; i++) {
+ if (i == 10) {
+ assertEquals(0, buf[i]);
+ } else {
+ assertEquals(64, buf[i]);
+ }
+ }
+ }
+
+ @Test
+ public void testRanges() throws Exception {
+ final FileDescriptor fd = RedactingFileDescriptor
+ .open(mContext, mFile, new long[] { 100, 200, 300, 400 }).getFileDescriptor();
+
+ final byte[] buf = new byte[10];
+ assertEquals(buf.length, Os.pread(fd, buf, 0, 10, 90));
+ assertArrayEquals(new byte[] { 64, 64, 64, 64, 64, 64, 64, 64, 64, 64 }, buf);
+
+ assertEquals(buf.length, Os.pread(fd, buf, 0, 10, 95));
+ assertArrayEquals(new byte[] { 64, 64, 64, 64, 64, 0, 0, 0, 0, 0 }, buf);
+
+ assertEquals(buf.length, Os.pread(fd, buf, 0, 10, 100));
+ assertArrayEquals(new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, buf);
+
+ assertEquals(buf.length, Os.pread(fd, buf, 0, 10, 195));
+ assertArrayEquals(new byte[] { 0, 0, 0, 0, 0, 64, 64, 64, 64, 64 }, buf);
+
+ assertEquals(buf.length, Os.pread(fd, buf, 0, 10, 395));
+ assertArrayEquals(new byte[] { 0, 0, 0, 0, 0, 64, 64, 64, 64, 64 }, buf);
+ }
+
+ @Test
+ public void testEntireFile() throws Exception {
+ final FileDescriptor fd = RedactingFileDescriptor
+ .open(mContext, mFile, new long[] { 0, 5_000_000 }).getFileDescriptor();
+
+ try (FileInputStream in = new FileInputStream(fd)) {
+ int val;
+ while ((val = in.read()) != -1) {
+ assertEquals(0, val);
+ }
+ }
+ }
+}
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