Bug 1272817 - Return early if file is empty + regression test. r=sebastian

MozReview-Commit-ID: FPdDr2t1wEy

--HG--
extra : rebase_source : 4fd7975262ac3af23d0a5f6b921cbe7a0863760e

mobile/android/base/java/org/mozilla/gecko/telemetry/stores/TelemetryJSONFilePingStore.java

@@ -150,6 +150,12 @@ public class TelemetryJSONFilePingStore implements TelemetryPingStore {
      * @return the JSON object from the given file or null if there is an error.
      */
     private JSONObject lockAndReadJSONFromFile(final File file) {
+        // lockAndReadFileAndCloseStream doesn't handle file size of 0.
+        if (file.length() == 0) {
+            Log.w(LOGTAG, "Unexpected empty file: " + file.getName() + ". Ignoring");
+            return null;
+        }
+
         final FileInputStream inputStream;
         try {
             inputStream = new FileInputStream(file);

mobile/android/tests/background/junit4/src/org/mozilla/gecko/telemetry/stores/TestTelemetryJSONFilePingStore.java

@@ -120,6 +120,14 @@ public class TestTelemetryJSONFilePingStore {
         }
     }
 
+    @Test // regression test: bug 1272817
+    public void testGetAllPingsHandlesEmptyFiles() throws Exception {
+        final int expectedPingCount = 3;
+        writeTestPingsToStore(expectedPingCount, "whatever");
+        assertTrue("Empty file is created", testStore.getPingFile(getDocID()).createNewFile());
+        assertEquals("Returned pings only contains valid files", expectedPingCount, testStore.getAllPings().size());
+    }
+
     @Test
     public void testMaybePrunePingsDoesNothingIfAtMax() throws Exception {
         final int pingCount = TelemetryJSONFilePingStore.MAX_PING_COUNT;