Add ApexContext API including methods to get paths for data directories.

This adds a new ApexContext class as a system API. Methods are included to
obtain paths to the APEX data directories.

In future the aim is for this ApexContext to be provided to code running
within an APEX automatically, so that data directory paths are available
only to the APEX that should access them. For R it is not feasible to
implement this, so for now a factory method is included to create an
ApexContext from the apex (module) name.

See go/apex-context-r for more information.

Bug: 141148175
Bug: 142484007
Test: ApexContextTest added
Change-Id: Iaf90e12383aa219a73a7818dab6cde6a850597ba

1 files changed, 98 insertions, 0 deletions

diff --git a/core/java/android/content/ApexContext.java b/core/java/android/content/ApexContext.java
new file mode 100644
index 000000000000..fe5cedca4654
--- /dev/null
+++ b/core/java/android/content/ApexContext.java
@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2020 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.content;
+
+import android.annotation.NonNull;
+import android.annotation.SystemApi;
+import android.os.Environment;
+import android.os.UserHandle;
+
+import java.io.File;
+import java.util.Objects;
+
+/**
+ * Provides information about the environment for a particular APEX.
+ *
+ * @hide
+ */
+@SystemApi
+public class ApexContext {
+
+    private static final String APEX_DATA = "apexdata";
+
+    /**
+     * Returns an ApexContext instance for the APEX with the provided {@code apexModuleName}.
+     *
+     * <p>To preserve the safety and integrity of APEX modules, you must only obtain the ApexContext
+     * for your specific APEX, and you <em>must never</em> attempt to obtain an ApexContext for
+     * another APEX.  Any coordination between APEXs must be performed through well-defined
+     * interfaces; attempting to directly read or write raw files belonging to another APEX will
+     * violate the hermetic storage requirements placed upon each module.
+     */
+    @NonNull
+    public static ApexContext getApexContext(@NonNull String apexModuleName) {
+        Objects.requireNonNull(apexModuleName, "apexModuleName cannot be null");
+        //TODO(b/141148175): Check that apexModuleName is an actual APEX name
+        return new ApexContext(apexModuleName);
+    }
+
+    private final String mApexModuleName;
+
+    private ApexContext(String apexModuleName) {
+        mApexModuleName = apexModuleName;
+    }
+
+    /**
+     * Returns the data directory for the APEX in device-encrypted, non-user-specific storage.
+     *
+     * <p>This directory is automatically created by the system for installed APEXes, and its
+     * contents will be rolled back if the APEX is rolled back.
+     */
+    @NonNull
+    public File getDeviceProtectedDataDir() {
+        return Environment.buildPath(
+                Environment.getDataMiscDirectory(), APEX_DATA, mApexModuleName);
+    }
+
+    /**
+     * Returns the data directory for the APEX in device-encrypted, user-specific storage for the
+     * specified {@code user}.
+     *
+     * <p>This directory is automatically created by the system for each user and for each installed
+     * APEX, and its contents will be rolled back if the APEX is rolled back.
+     */
+    @NonNull
+    public File getDeviceProtectedDataDirForUser(@NonNull UserHandle user) {
+        return Environment.buildPath(
+                Environment.getDataMiscDeDirectory(user.getIdentifier()), APEX_DATA,
+                mApexModuleName);
+    }
+
+    /**
+     * Returns the data directory for the APEX in credential-encrypted, user-specific storage for
+     * the specified {@code user}.
+     *
+     * <p>This directory is automatically created by the system for each user and for each installed
+     * APEX, and its contents will be rolled back if the APEX is rolled back.
+     */
+    @NonNull
+    public File getCredentialProtectedDataDirForUser(@NonNull UserHandle user) {
+        return Environment.buildPath(
+                Environment.getDataMiscCeDirectory(user.getIdentifier()), APEX_DATA,
+                mApexModuleName);
+    }
+}