Live viewer: add escape support

Closes #136.

live-viewer/index.html

@@ -22,10 +22,19 @@ <h1>Live URL Viewer</h1>
   <label for="url">URL:</label>
   <input id="url" value="https://example.com/" autofocus>
 
+  <label for="url-escaped">URL with escapes:</label>
+  <input id="url-escaped" value="https://example.com/">
+
   <label for="base">Base URL:</label>
   <input id="base" value="about:blank">
 </form>
 
+<details>
+  <summary>How do I use "URL with escapes?"</summary>
+
+  <p>Most of the time, you don't need to worry about this. But if you want to test characters outside of the U+0021 (!) through U+007E (~) range, which can be harder to input or to visually distinguish, you can use this field. Any strings of the form <samp>\u{<var>number</var>}</samp> will be decoded to their corresponding Unicode code point. So for example, you could test how null characters are processed by the URL parser by using the input <samp>test:\u{0}</samp>.
+</details>
+
 <h2>Browser's URL components</h2>
 
 <table class="output" id="browser-output">

live-viewer/live-viewer.mjs

@@ -1,6 +1,7 @@
 import whatwgURL from "./whatwg-url.mjs";
 
 const urlInput = document.querySelector("#url");
+const urlEscapedInput = document.querySelector("#url-escaped");
 const baseInput = document.querySelector("#base");
 
 const te = new TextEncoder();
@@ -19,8 +20,13 @@ const components = [
   "origin"
 ];
 
+urlInput.addEventListener("input", updateEscaped);
+urlEscapedInput.addEventListener("input", updateUnescaped);
+
 urlInput.addEventListener("input", update);
+urlEscapedInput.addEventListener("input", update);
 baseInput.addEventListener("input", update);
+
 window.addEventListener("hashchange", setFromFragment);
 setFromFragment();
 update();
@@ -54,6 +60,14 @@ function setResult(kind, result, mismatchedComponents) {
   }
 }
 
+function updateEscaped() {
+  urlEscapedInput.value = escape(urlInput.value);
+}
+
+function updateUnescaped() {
+  urlInput.value = unescape(urlEscapedInput.value);
+}
+
 function setComponentElValue(componentEl, value) {
   const isEmptyString = value === "";
 
@@ -120,6 +134,7 @@ function setFromFragment() {
     console.warn("base hash parameter was not deserializable.");
   }
 
+  updateEscaped();
   update();
 }
 
@@ -139,3 +154,27 @@ function decodeFromBase64(encoded) {
   const originalString = td.decode(bytes);
   return originalString;
 }
+
+function escape(rawString) {
+  return rawString
+    .replaceAll(
+      "\\u",
+      "\\\\u"
+    )
+    .replaceAll(
+      /[^\u{0021}-\u{007E}]/ug,
+      c => `\\u{${c.codePointAt(0).toString(16).padStart(4, "0")}}`
+    );
+}
+
+function unescape(escapedString) {
+  return escapedString
+    .replaceAll(
+      /(?<!\\)\\u\{([0-9a-fA-F]+)\}/ug,
+      (_, c) => String.fromCodePoint(Number.parseInt(c, 16))
+    )
+    .replaceAll(
+      "\\\\u",
+      "\\u"
+    );
+}

live-viewer/style.css

@@ -1,9 +1,9 @@
 * {
-  font-family: Georgia;
   box-sizing: border-box;
 }
 
 body {
+  font-family: Georgia;
   max-width: 70em;
   margin: 12px;
 }
@@ -88,3 +88,11 @@ form input {
 .output td.empty-string:not(.fail) {
   color: #CCC;
 }
+
+summary {
+  cursor: pointer;
+}
+
+samp {
+  font-family: monospace;
+}