License and usage example

Author: André Ribas

LICENSE

@@ -0,0 +1,7 @@
+Copyright 2026 André Ribas
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

test/exampleOfUse.js

@@ -0,0 +1,67 @@
+(async function () {
+    const BASE = "https://h4f.me/url?ref=";
+    const SELF_HOST = location.hostname;
+    const SKIP_SCHEMES = ["mailto:", "tel:", "sms:", "whatsapp:", "tg:", "skype:", "javascript:"];
+    const RECEIVER_PUBLIC_KEY = "TOKEN_HERE";
+
+    function b64uToBuf(s) {
+        s = s.replace(/-/g, "+").replace(/_/g, "/");
+        s = s.padEnd(Math.ceil(s.length / 4) * 4, "=");
+        return Uint8Array.from(atob(s), c => c.charCodeAt(0));
+    }
+
+    function bufToB64u(b) {
+        return btoa(String.fromCharCode(...b)).replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");
+    }
+
+    async function encrypt(message) {
+        const receiverKeyRaw = b64uToBuf(RECEIVER_PUBLIC_KEY);
+        const eph = await crypto.subtle.generateKey({ name: "X25519" }, true, ["deriveBits"]);
+        const receiverKey = await crypto.subtle.importKey("raw", receiverKeyRaw, { name: "X25519" }, false, []);
+        const shared = await crypto.subtle.deriveBits({ name: "X25519", public: receiverKey }, eph.privateKey, 256);
+        const keyMaterial = await crypto.subtle.digest("SHA-256", shared);
+        const aesKey = await crypto.subtle.importKey("raw", keyMaterial, { name: "AES-GCM" }, false, ["encrypt"]);
+        const iv = crypto.getRandomValues(new Uint8Array(12));
+        const encrypted = new Uint8Array(await crypto.subtle.encrypt(
+            { name: "AES-GCM", iv },
+            aesKey,
+            new TextEncoder().encode(message)
+        ));
+        const ephPubRaw = new Uint8Array(await crypto.subtle.exportKey("raw", eph.publicKey));
+        const payload = new Uint8Array(ephPubRaw.length + iv.length + encrypted.length);
+        payload.set(ephPubRaw, 0);
+        payload.set(iv, 32);
+        payload.set(encrypted, 44);
+        return bufToB64u(payload);
+    }
+
+    function isInternal(href) {
+        if (href.startsWith("/")) return true;
+        try {
+            const u = new URL(href, location.origin);
+            return u.hostname === SELF_HOST;
+        } catch {
+            return true;
+        }
+    }
+
+    async function rewrite() {
+        const links = [...document.querySelectorAll("a[href]")];
+        for (const a of links) {
+            const href = a.getAttribute("href");
+            if (!href) continue;
+            if (href.startsWith("#")) continue;
+            if (SKIP_SCHEMES.some(s => href.toLowerCase().startsWith(s))) continue;
+            if (href.startsWith(BASE)) continue;
+            if (isInternal(href)) continue;
+            const encrypted = await encrypt(href);
+            a.setAttribute("href", BASE + encrypted);
+        }
+    }
+
+    if (document.readyState === "loading") {
+        document.addEventListener("DOMContentLoaded", rewrite);
+    } else {
+        rewrite();
+    }
+})();