feat(app): implement Google Play App Licensing

Signed-off-by: YuutaW <17158086+Trumeet@users.noreply.github.com>

1 files changed, 63 insertions, 0 deletions

diff --git a/app/src/main/java/moe/yuuta/gplicense/PreferenceObfuscator.java b/app/src/main/java/moe/yuuta/gplicense/PreferenceObfuscator.java
new file mode 100644
index 0000000..0b02276
--- /dev/null
+++ b/app/src/main/java/moe/yuuta/gplicense/PreferenceObfuscator.java
@@ -0,0 +1,63 @@
+package moe.yuuta.gplicense;
+
+import android.content.SharedPreferences;
+
+import com.elvishew.xlog.Logger;
+import com.elvishew.xlog.XLog;
+
+/**
+ * An wrapper for SharedPreferences that transparently performs data obfuscation.
+ */
+public class PreferenceObfuscator {
+
+    private static final Logger logger = XLog.tag("PrefObfs").build();
+
+    private final SharedPreferences mPreferences;
+    private final Obfuscator mObfuscator;
+    private SharedPreferences.Editor mEditor;
+
+    /**
+     * Constructor.
+     *
+     * @param sp A SharedPreferences instance provided by the system.
+     * @param o The Obfuscator to use when reading or writing data.
+     */
+    public PreferenceObfuscator(SharedPreferences sp, Obfuscator o) {
+        mPreferences = sp;
+        mObfuscator = o;
+        mEditor = null;
+    }
+
+    public void putString(String key, String value) {
+        if (mEditor == null) {
+            mEditor = mPreferences.edit();
+        }
+        String obfuscatedValue = mObfuscator.obfuscate(value, key);
+        mEditor.putString(key, obfuscatedValue);
+    }
+
+    public String getString(String key, String defValue) {
+        String result;
+        String value = mPreferences.getString(key, null);
+        if (value != null) {
+            try {
+                result = mObfuscator.unobfuscate(value, key);
+            } catch (ValidationException e) {
+                // Unable to unobfuscate, data corrupt or tampered
+                logger.w("Validation error while reading preference: " + key);
+                result = defValue;
+            }
+        } else {
+            // Preference not found
+            result = defValue;
+        }
+        return result;
+    }
+
+    public void commit() {
+        if (mEditor != null) {
+            mEditor.commit();
+            mEditor = null;
+        }
+    }
+}
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