add stub download implementation

static/js/web-install.js

@@ -28,6 +28,36 @@ async function unlockBootloader() {
     await fastboot.receive();
 }
 
+async function downloadRelease() {
+    const webusb = await Adb.open("WebUSB");
+
+    if (!webusb.isFastboot()) {
+        console.log("error: not in fastboot mode");
+    }
+
+    console.log("connecting with fastboot");
+
+    const fastboot = await webusb.connectFastboot();
+    await fastboot.send("getvar:product");
+    const response = await fastboot.receive();
+    if (fastboot.get_cmd(response) == "FAIL") {
+        throw new Error("getvar product failed");
+    }
+    const decoder = new TextDecoder();
+    const product = decoder.decode(fastboot.get_payload(response));
+
+    const baseUrl = "https://releases.grapheneos.org/";
+    const metadata = await (await fetch(baseUrl + product + "-stable")).text();
+    const buildNumber = metadata.split(" ")[0];
+    const downloadUrl = baseUrl + product + "-factory-" + buildNumber + ".zip";
+    console.log(downloadUrl);
+
+    // Download factory images
+    //
+    // Need to do this in a way that works well with huge files, particularly since the zip needs
+    // to be extracted. Could potentially split it up on the server if this works out badly.
+}
+
 async function lockBootloader() {
     const webusb = await Adb.open("WebUSB");
 
@@ -53,6 +83,10 @@ if ("usb" in navigator) {
     unlockBootloaderButton.disabled = false;
     unlockBootloaderButton.onclick = unlockBootloader;
 
+    const downloadReleaseButton = document.getElementById("download-release");
+    downloadReleaseButton.disabled = false;
+    downloadReleaseButton.onclick = downloadRelease;
+
     const lockBootloaderButton = document.getElementById("lock-bootloader");
     lockBootloaderButton.disabled = false;
     lockBootloaderButton.onclick = lockBootloader;

static/web-install.html

@@ -139,6 +139,19 @@
                 confirm.</p>
             </section>
 
+            <section id="obtaining-factory-images">
+                <h2><a href="#obtaining-factory-images">Obtaining factory images</a></h2>
+
+                <p>You need to obtain the GrapheneOS factory images for your device to proceed with
+                the installation process.</p>
+
+                <p>Press the button below to start the download:</p>
+
+                <button id="download-release" disabled="disabled">Download release</button>
+
+                <p><strong>Download not implemented yet.</strong></p>
+            </section>
+
             <section>
                 <h2>Incomplete</h2>
             </section>