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node_modules/@weborigami/async-tree/src/drivers/ExplorableSiteTree.js

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+import SiteTree from "./SiteTree.js";
+
+/**
+ * A [SiteTree](SiteTree.html) that implements the [JSON Keys](jsonKeys.html)
+ * protocol. This enables a `keys()` method that can return the keys of a site
+ * route even though such a mechanism is not built into the HTTP protocol.
+ */
+export default class ExplorableSiteTree extends SiteTree {
+  constructor(...args) {
+    super(...args);
+    this.serverKeysPromise = undefined;
+  }
+
+  async getServerKeys() {
+    // We use a promise to ensure we only check for keys once.
+    const href = new URL(".keys.json", this.href).href;
+    this.serverKeysPromise ??= fetch(href)
+      .then((response) => (response.ok ? response.text() : null))
+      .then((text) => {
+        try {
+          return text ? JSON.parse(text) : null;
+        } catch (error) {
+          // Got a response, but it's not JSON. Most likely the site doesn't
+          // actually have a .keys.json file, and is returning a Not Found page,
+          // but hasn't set the correct 404 status code.
+          return null;
+        }
+      });
+    return this.serverKeysPromise;
+  }
+
+  /**
+   * Returns the keys of the site route. For this to work, the route must have a
+   * `.keys.json` file that contains a JSON array of string keys.
+   *
+   * @returns {Promise<Iterable<string>>}
+   */
+  async keys() {
+    const serverKeys = await this.getServerKeys();
+    return serverKeys ?? [];
+  }
+
+  processResponse(response) {
+    // If the response was redirected to a route that ends with a slash, and the
+    // site is an explorable site, we return a tree for the new route.
+    if (response.ok && response.redirected && response.url.endsWith("/")) {
+      return Reflect.construct(this.constructor, [response.url]);
+    }
+
+    return super.processResponse(response);
+  }
+}