1 files changed, 88 insertions, 0 deletions
diff --git a/dom/localstorage/test/unit/test_largeItems.js b/dom/localstorage/test/unit/test_largeItems.js
new file mode 100644
index 0000000000..3ea6bd21b4
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+++ b/dom/localstorage/test/unit/test_largeItems.js
@@ -0,0 +1,88 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+/**
+ * Test repeatedly setting values that are just under the LocalStorage quota
+ * limit without yielding control flow in order to verify that the write
+ * optimizer is present / works. If there was no write optimizer present, the
+ * IPC message size limit would be exceeded, resulting in a crash.
+ */
+
+add_task(async function testSteps() {
+  const globalLimitKB = 5 * 1024;
+
+  // 18 and more iterations would produce an IPC message with size greater than
+  // 256 MB if write optimizer was not present. This number was determined
+  // experimentally by running the test with disabled write optimizer.
+  const numberOfIterations = 18;
+
+  const randomStringBlockSize = 65536;
+
+  // We need to use a random string because LS internally tries to compress
+  // values.
+  function getRandomString(size) {
+    let crypto = this.window ? this.window.crypto : this.crypto;
+    let decoder = new TextDecoder("ISO-8859-2");
+
+    function getRandomStringBlock(array) {
+      crypto.getRandomValues(array);
+      return decoder.decode(array);
+    }
+
+    let string = "";
+
+    let quotient = size / randomStringBlockSize;
+    if (quotient) {
+      let array = new Uint8Array(randomStringBlockSize);
+      for (let i = 1; i <= quotient; i++) {
+        string += getRandomStringBlock(array);
+      }
+    }
+
+    let remainder = size % randomStringBlockSize;
+    if (remainder) {
+      let array = new Uint8Array(remainder);
+      string += getRandomStringBlock(array);
+    }
+
+    return string;
+  }
+
+  const data = {};
+  data.key = "foo";
+  data.value = getRandomString(
+    globalLimitKB * 1024 -
+      data.key.length -
+      numberOfIterations.toString().length
+  );
+
+  info("Setting pref");
+
+  // By disabling snapshot reusing, we guarantee that the snapshot will be
+  // checkpointed once control returns to the event loop.
+  if (this.window) {
+    await SpecialPowers.pushPrefEnv({
+      set: [["dom.storage.snapshot_reusing", false]],
+    });
+  } else {
+    Services.prefs.setBoolPref("dom.storage.snapshot_reusing", false);
+  }
+
+  info("Getting storage");
+
+  let storage = getLocalStorage();
+
+  info("Adding/updating item");
+
+  for (var i = 0; i < numberOfIterations; i++) {
+    storage.setItem(data.key, data.value + i);
+  }
+
+  info("Returning to event loop");
+
+  await returnToEventLoop();
+
+  ok(!storage.hasSnapshot, "Snapshot successfully finished");
+});