Improve Splash screen download indicators

- Calculate package list download progress percentage if possible. This
  requires that the response headers contain the total length of the
  content, which is not guaranteed.
- Set exclusion list download progress to 100 when done. Previously
  this would be left to 0 if the response headers didn't contain the
  content length.
- Set package list download progress to 100 when done, even if the
  download fails. Strictly speaking this wouldn't be necessary since
  the progress bar is hidden after this step, but it might prevent
  issues in the future if the UI is changed.
- Reset all progress to 0 if user attempts to reconnect after some part
  of the process has failed.

src/components/mixins/SplashMixin.vue

@@ -44,6 +44,7 @@ export default class SplashMixin extends Vue {
         };
 
         ThunderstorePackages.EXCLUSIONS = await ConnectionProvider.instance.getExclusions(showProgress);
+        this.getRequestItem('ExclusionsList').setProgress(100);
     }
 
     // Get the list of Thunderstore mods from API.
@@ -62,6 +63,8 @@ export default class SplashMixin extends Vue {
             this.isOffline = true;
             this.heroTitle = 'Failed to get mods from Thunderstore';
             this.loadingText = 'You may be offline or Thunderstore is unavailabe. Checking cache.';
+        } finally {
+            this.getRequestItem('ThunderstoreDownload').setProgress(100);
         }
 
         if (response) {

src/pages/Splash.vue

@@ -194,6 +194,9 @@ export default class Splash extends mixins(SplashMixin) {
     }
 
     retryConnection() {
+        this.getRequestItem('UpdateCheck').setProgress(0);
+        this.getRequestItem('ExclusionsList').setProgress(0);
+        this.getRequestItem('ThunderstoreDownload').setProgress(0);
         this.isOffline = false;
         this.checkForUpdates();
     }

src/utils/HttpUtils.ts

@@ -31,11 +31,7 @@ export const getAxiosWithTimeouts = (responseTimeout = 5000, totalTimeout = 1000
 };
 
 interface LongRunningRequestOptions {
-    /**
-     * Custom function to be called when progress is made. Doesn't work
-     * properly currently, since the progress percentage can't be
-     * calculated because the total length of the content isn't known.
-     */
+    /** Custom function to be called when progress is made. */
     downloadProgressed?: DownloadProgressed;
     /**
      * Time (in ms) the request has to trigger the first download
@@ -84,10 +80,9 @@ export const makeLongRunningGetRequest = async (
         rollingTimeout = setTimeout(abort, transmissionTimeout);
 
         if (typeof downloadProgressed === "function") {
-            // TODO: Progress percentage can't be calculated since the
-            // content length is unknown. Looks like this hasn't worked
-            // in a while.
-            downloadProgressed(0);
+            // Backend might not provided total content length.
+            const percent = progress.total ? (progress.loaded / progress.total) * 100 : 0;
+            downloadProgressed(percent);
         }
     }