From 1964c9c4857f179d67fd3be55d28119dfb533af0 Mon Sep 17 00:00:00 2001
From: David Lechner <david@pybricks.com>
Date: Mon, 12 Apr 2021 13:24:10 -0500
Subject: [PATCH] Add timeout while waiting for checksum

This adds a timeout while waiting for the checksum from the hub when
downloading and running a program. Without this, we can get stuck in
the "loading" state if the hub doesn't respond as expected. This can
happen, for example, if a program is started with the hub button at the
same time as the start button in Pybricks Code is pressed.

Issue: https://github.com/pybricks/support/issues/301
---
 src/hub/sagas.ts | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/src/hub/sagas.ts b/src/hub/sagas.ts
index 55eedb29..cd795dcd 100644
--- a/src/hub/sagas.ts
+++ b/src/hub/sagas.ts
@@ -4,6 +4,7 @@
 import {
     SagaGenerator,
     actionChannel,
+    delay,
     getContext,
     put,
     race,
@@ -108,7 +109,19 @@ function* downloadAndRun(_action: HubDownloadAndRunAction): Generator {
         return;
     }
 
-    const checksumAction = yield* take(checksumChannel);
+    const { checksumAction, checksumTimeout } = yield* race({
+        checksumAction: take(checksumChannel),
+        checksumTimeout: delay(1000),
+    });
+
+    if (checksumTimeout) {
+        console.error(`timeout waiting for checksum`);
+        yield* put(didFailToFinishDownload());
+        return;
+    }
+
+    defined(checksumAction);
+
     if (checksumAction.checksum !== (0xff ^ xor8(sizeBuf))) {
         console.error(
             `bad checksum ${checksumAction.checksum} vs ${0xff ^ xor8(sizeBuf)}`,
@@ -136,7 +149,20 @@ function* downloadAndRun(_action: HubDownloadAndRunAction): Generator {
             }
             // TODO: dispatch progress
         }
-        const checksumAction = yield* take(checksumChannel);
+
+        const { checksumAction, checksumTimeout } = yield* race({
+            checksumAction: take(checksumChannel),
+            checksumTimeout: delay(1000),
+        });
+
+        if (checksumTimeout) {
+            console.error(`timeout waiting for checksum`);
+            yield* put(didFailToFinishDownload());
+            return;
+        }
+
+        defined(checksumAction);
+
         if (checksumAction.checksum !== (0xff ^ xor8(chunk))) {
             console.error(
                 `bad checksum ${checksumAction.checksum} vs ${0xff ^ xor8(chunk)}`,