1 files changed, 33 insertions, 0 deletions
diff --git a/testing/web-platform/tests/serial/resources/common.js b/testing/web-platform/tests/serial/resources/common.js
new file mode 100644
index 0000000000..5177f83a86
--- /dev/null
+++ b/testing/web-platform/tests/serial/resources/common.js
@@ -0,0 +1,33 @@
+// Compare two Uint8Arrays.
+function compareArrays(actual, expected) {
+  assert_true(actual instanceof Uint8Array, 'actual is Uint8Array');
+  assert_true(expected instanceof Uint8Array, 'expected is Uint8Array');
+  assert_equals(actual.byteLength, expected.byteLength, 'lengths equal');
+  for (let i = 0; i < expected.byteLength; ++i)
+    assert_equals(actual[i], expected[i], `Mismatch at position ${i}.`);
+}
+
+// Reads from |reader| until at least |targetLength| is read or the stream is
+// closed. The data is returned as a combined Uint8Array.
+async function readWithLength(reader, targetLength) {
+  const chunks = [];
+  let actualLength = 0;
+
+  while (true) {
+    let {value, done} = await reader.read();
+    chunks.push(value);
+    actualLength += value.byteLength;
+
+    if (actualLength >= targetLength || done) {
+      // It would be better to allocate |buffer| up front with the number of
+      // of bytes expected but this is the best that can be done without a
+      // BYOB reader to control the amount of data read.
+      const buffer = new Uint8Array(actualLength);
+      chunks.reduce((offset, chunk) => {
+        buffer.set(chunk, offset);
+        return offset + chunk.byteLength;
+      }, 0);
+      return buffer;
+    }
+  }
+}