1 files changed, 32 insertions, 0 deletions
diff --git a/testing/web-platform/tests/encoding/resources/decoding-helpers.js b/testing/web-platform/tests/encoding/resources/decoding-helpers.js
new file mode 100644
index 0000000000..78e52da014
--- /dev/null
+++ b/testing/web-platform/tests/encoding/resources/decoding-helpers.js
@@ -0,0 +1,32 @@
+// Decode an URL encoded string, using XHR and data: URL. Returns a Promise.
+function decode(label, url_encoded_string) {
+  return new Promise((resolve, reject) => {
+    const req = new XMLHttpRequest;
+    req.open('GET', `data:text/plain,${url_encoded_string}`);
+    req.overrideMimeType(`text/plain; charset="${label}"`);
+    req.send();
+    req.onload = () => resolve(req.responseText);
+    req.onerror = () => reject(new Error(req.statusText));
+  });
+}
+
+// Convert code units in a decoded string into: "U+0001/U+0002/...'
+function to_code_units(string) {
+  return string.split('')
+    .map(unit => unit.charCodeAt(0))
+    .map(code => 'U+' + ('0000' + code.toString(16).toUpperCase()).slice(-4))
+    .join('/');
+}
+
+function decode_test(label,
+                     url_encoded_input,
+                     expected_code_units,
+                     description) {
+  promise_test(() => {
+    return decode(label, url_encoded_input)
+      .then(decoded => to_code_units(decoded))
+      .then(actual => {
+        assert_equals(actual, expected_code_units, `Decoding with ${label}`);
+      });
+  }, description);
+}