firmware: Don't add checksums when not needed.

This fixes an issue where the EV3 firmware had checksums appended to
it that made its size not align to the sector size, causing flashing
to fail.

Author: jaguilar

src/firmware/sagas.ts

@@ -351,32 +351,20 @@ function* loadFirmware(
         'Expected metadata to be v2.x',
     );
 
-    const firmware = new Uint8Array(firmwareBase.length + 4);
-    const firmwareView = new DataView(firmware.buffer);
-
-    firmware.set(firmwareBase);
-
-    // empty string means use default name (don't write over firmware)
-    if (hubName) {
-        firmware.set(encodeHubName(hubName, metadata), metadata['hub-name-offset']);
-    }
-
-    const checksum = (function () {
+    const [checksumFunc, checksumExtraLength] = (() => {
         switch (metadata['checksum-type']) {
             case 'sum':
-                return sumComplement32(
-                    firmwareIterator(firmwareView, metadata['checksum-size']),
-                );
+                return [sumComplement32, 4];
             case 'crc32':
-                return crc32(firmwareIterator(firmwareView, metadata['checksum-size']));
+                return [crc32, 4];
             case 'none':
-                return null;
+                return [null, 0];
             default:
-                return undefined;
+                return [undefined, 0];
         }
     })();
 
-    if (checksum === undefined) {
+    if (checksumFunc === undefined) {
         // FIXME: we should return error/throw instead
         yield* put(
             didFailToFinish(
@@ -391,8 +379,22 @@ function* loadFirmware(
         throw new Error('unreachable');
     }
 
-    if (checksum !== null) {
-        firmwareView.setUint32(firmwareBase.length, checksum, true);
+    const firmware = new Uint8Array(firmwareBase.length + checksumExtraLength);
+    const firmwareView = new DataView(firmware.buffer);
+
+    firmware.set(firmwareBase);
+
+    // empty string means use default name (don't write over firmware)
+    if (hubName) {
+        firmware.set(encodeHubName(hubName, metadata), metadata['hub-name-offset']);
+    }
+
+    if (checksumFunc !== null) {
+        firmwareView.setUint32(
+            firmwareBase.length,
+            checksumFunc(firmwareIterator(firmwareView, metadata['checksum-size'])),
+            true,
+        );
     }
 
     return { firmware, deviceId: metadata['device-id'] };