Add a PersistentInt class.
This implements a simple integer written to disk backed by
AtomicFile.
Bug: 230289468
Test: new unit test
Ignore-AOSP-First: in a topic with internal-only changes
Change-Id: I1c73c8ac2429f92153cfba3b006b4374e75e65df
diff --git a/service-t/src/com/android/server/net/PersistentInt.java b/service-t/src/com/android/server/net/PersistentInt.java
new file mode 100644
index 0000000..c212b77
--- /dev/null
+++ b/service-t/src/com/android/server/net/PersistentInt.java
@@ -0,0 +1,108 @@
+/*
+ * Copyright (C) 2022 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 com.android.server.net;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.util.AtomicFile;
+import android.util.SystemConfigFileCommitEventLogger;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+/**
+ * A simple integer backed by an on-disk {@link AtomicFile}. Not thread-safe.
+ */
+public class PersistentInt {
+ private final String mPath;
+ private final AtomicFile mFile;
+
+ /**
+ * Constructs a new {@code PersistentInt}. The counter is set to 0 if the file does not exist.
+ * Before returning, the constructor checks that the file is readable and writable. This
+ * indicates that in the future {@link #get} and {@link #set} are likely to succeed,
+ * though other events (data corruption, other code deleting the file, etc.) may cause these
+ * calls to fail in the future.
+ *
+ * @param path the path of the file to use.
+ * @param logger the logger
+ * @throws IOException the counter could not be read or written
+ */
+ public PersistentInt(@NonNull String path, @Nullable SystemConfigFileCommitEventLogger logger)
+ throws IOException {
+ mPath = path;
+ mFile = new AtomicFile(new File(path), logger);
+ checkReadWrite();
+ }
+
+ private void checkReadWrite() throws IOException {
+ int value;
+ try {
+ value = get();
+ } catch (FileNotFoundException e) {
+ // Counter does not exist. Attempt to initialize to 0.
+ // Note that we cannot tell here if the file does not exist or if opening it failed,
+ // because in Java both of those throw FileNotFoundException.
+ value = 0;
+ }
+ set(value);
+ get();
+ // No exceptions? Good.
+ }
+
+ /**
+ * Gets the current value.
+ *
+ * @return the current value of the counter.
+ * @throws IOException if reading the value failed.
+ */
+ public int get() throws IOException {
+ try (FileInputStream fin = mFile.openRead();
+ DataInputStream din = new DataInputStream(fin)) {
+ return din.readInt();
+ }
+ }
+
+ /**
+ * Sets the current value.
+ * @param value the value to set
+ * @throws IOException if writing the value failed.
+ */
+ public void set(int value) throws IOException {
+ FileOutputStream fout = null;
+ try {
+ fout = mFile.startWrite();
+ DataOutputStream dout = new DataOutputStream(fout);
+ dout.writeInt(value);
+ mFile.finishWrite(fout);
+ } catch (IOException e) {
+ if (fout != null) {
+ mFile.failWrite(fout);
+ }
+ throw e;
+ }
+ }
+
+ public String getPath() {
+ return mPath;
+ }
+}
diff --git a/tests/unit/java/com/android/server/net/PersistentIntTest.kt b/tests/unit/java/com/android/server/net/PersistentIntTest.kt
new file mode 100644
index 0000000..9509d38
--- /dev/null
+++ b/tests/unit/java/com/android/server/net/PersistentIntTest.kt
@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 2022 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 com.android.server.net
+
+import android.util.SystemConfigFileCommitEventLogger
+import com.android.testutils.assertThrows
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import java.io.File
+import java.io.IOException
+import java.nio.file.Files
+import java.nio.file.Path
+import java.nio.file.attribute.PosixFilePermission
+import java.nio.file.attribute.PosixFilePermission.OWNER_EXECUTE
+import java.nio.file.attribute.PosixFilePermission.OWNER_READ
+import java.nio.file.attribute.PosixFilePermission.OWNER_WRITE
+import java.util.Random
+import kotlin.test.assertEquals
+
+class PersistentIntTest {
+ val tempFilesCreated = mutableSetOf<Path>()
+ lateinit var tempDir: Path
+
+ @Before
+ fun setUp() {
+ tempDir = Files.createTempDirectory("tmp.PersistentIntTest.")
+ }
+
+ @After
+ fun tearDown() {
+ var permissions = setOf(OWNER_READ, OWNER_WRITE, OWNER_EXECUTE)
+ Files.setPosixFilePermissions(tempDir, permissions)
+
+ for (file in tempFilesCreated) {
+ Files.deleteIfExists(file)
+ }
+ Files.delete(tempDir)
+ }
+
+ @Test
+ fun testNormalReadWrite() {
+ // New, initialized to 0.
+ val pi = createPersistentInt()
+ assertEquals(0, pi.get())
+ pi.set(12345)
+ assertEquals(12345, pi.get())
+
+ // Existing.
+ val pi2 = createPersistentInt(pathOf(pi))
+ assertEquals(12345, pi2.get())
+ }
+
+ @Test
+ fun testReadOrWriteFailsInCreate() {
+ setWritable(tempDir, false)
+ assertThrows(IOException::class.java) {
+ createPersistentInt()
+ }
+ }
+
+ @Test
+ fun testReadOrWriteFailsAfterCreate() {
+ val pi = createPersistentInt()
+ pi.set(42)
+ assertEquals(42, pi.get())
+
+ val path = pathOf(pi)
+ setReadable(path, false)
+ assertThrows(IOException::class.java) { pi.get() }
+ pi.set(77)
+
+ setReadable(path, true)
+ setWritable(path, false)
+ setWritable(tempDir, false) // Writing creates a new file+renames, make this fail.
+ assertThrows(IOException::class.java) { pi.set(99) }
+ assertEquals(77, pi.get())
+ }
+
+ fun addOrRemovePermission(p: Path, permission: PosixFilePermission, add: Boolean) {
+ val permissions = Files.getPosixFilePermissions(p)
+ if (add) {
+ permissions.add(permission)
+ } else {
+ permissions.remove(permission)
+ }
+ Files.setPosixFilePermissions(p, permissions)
+ }
+
+ fun setReadable(p: Path, readable: Boolean) {
+ addOrRemovePermission(p, OWNER_READ, readable)
+ }
+
+ fun setWritable(p: Path, writable: Boolean) {
+ addOrRemovePermission(p, OWNER_WRITE, writable)
+ }
+
+ fun pathOf(pi: PersistentInt): Path {
+ return File(pi.path).toPath()
+ }
+
+ fun createPersistentInt(path: Path = randomTempPath()): PersistentInt {
+ tempFilesCreated.add(path)
+ return PersistentInt(path.toString(),
+ SystemConfigFileCommitEventLogger("PersistentIntTest"))
+ }
+
+ fun randomTempPath(): Path {
+ return tempDir.resolve(Integer.toHexString(Random().nextInt())).also {
+ tempFilesCreated.add(it)
+ }
+ }
+}
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