From b43e8d9e0411df701d8ff9d27575aedfcd3170dd Mon Sep 17 00:00:00 2001
From: Michael Auer <michael.auer@heigit.org>
Date: Wed, 11 Oct 2023 08:50:21 +0200
Subject: [PATCH] fix(frontend): improve network error handling while waiting
 for results

Previously a network error stopped the result page from polling and the user only saw an endless spinner.
Now polling goes on even if flask is temporarily not available, e.g. while restarting.
Polling goes on until flask sends a status of SUCCESS or ERROR

Closes: #280
---
 client-src/shared/poll/poll.js           |  4 ++--
 client-src/shared/poll/pollUntilValid.js | 21 +++++++++++++++++++--
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/client-src/shared/poll/poll.js b/client-src/shared/poll/poll.js
index d2572efb..02b00a51 100644
--- a/client-src/shared/poll/poll.js
+++ b/client-src/shared/poll/poll.js
@@ -67,11 +67,11 @@ async function poll(url, prefix) {
     }
 
     try {
-        return PollUntilValid.poll(url, validateFn, 1000, onValid, onProgress, onError);
+        return await PollUntilValid.poll(url, validateFn, 1000, onValid, onProgress, onError);
     } catch (e) {
         // Network Error or other reason why the request could not be completed
         console.log(e);
-        handleError(prefix);
+        handleError(prefix, e);
         return null;
     }
 }
diff --git a/client-src/shared/poll/pollUntilValid.js b/client-src/shared/poll/pollUntilValid.js
index 315c6820..40adac04 100644
--- a/client-src/shared/poll/pollUntilValid.js
+++ b/client-src/shared/poll/pollUntilValid.js
@@ -27,8 +27,24 @@ class PollUntilValid {
         onError = () => {},
     ) {
         do {
-            /* eslint-disable no-await-in-loop */
-            const response = await fetch(url);
+            let response;
+            try {
+                /* eslint-disable no-await-in-loop */
+                response = await fetch(url);
+            } catch (error) {
+                if (error instanceof TypeError) {
+                    // Chrome and Firefox use different Error messages, so it's hard to be more
+                    // specific than checking for TypeError
+                    // see: https://developer.mozilla.org/en-US/docs/Web/API/fetch#exceptions
+                    console.log("NetworkError, continue retrying", error);
+                    await PollUntilValid.wait(5000);
+                } else {
+                    throw error;
+                }
+            }
+
+            // eslint-disable-next-line no-continue
+            if (!response) continue;
 
             // if response code is not between 200-299
             if (!response.ok) {
@@ -43,6 +59,7 @@ class PollUntilValid {
                 await onValid(response);
                 return response;
             }
+
             /* eslint-enable */
         } while (true);
     }