[WPE][GTK] API test TestDownloads `/webkit/Downloads/local-file-err…

…or` is flaky

https://bugs.webkit.org/show_bug.cgi?id=259210

Reviewed by Carlos Garcia Campos.

In one of the subtests, we start downloading a local file and then
immediately cancel it.

When the download completes fast, `WebKitDownloadClient::didFinish()`
method can be called twice. Firstly, because the download is actually
completed, and secondly, from `Download::cancel()`'s completion handler,
which we set in `webkit_download_cancel()'.

Since we set `m_download` to `nullptr`
in `WebKitDownloadClient::didFinish()`, the second call will crash.

The solution is to call `WebKitDownloadClient::legacyDidCancel()`
instead of `WebKitDownloadClient::didFinish()` from the download's
cancel completion handler.

* Source/WebKit/UIProcess/API/glib/WebKitDownload.cpp:
* Source/WebKit/UIProcess/API/glib/WebKitDownloadClient.cpp:

Canonical link: https://commits.webkit.org/266725@main

Source/WebKit/UIProcess/API/glib/WebKitDownload.cpp

@@ -428,14 +428,6 @@ void webkitDownloadCancelled(WebKitDownload* download)
 
 void webkitDownloadFinished(WebKitDownload* download)
 {
-    if (download->priv->isCancelled) {
-        // Since cancellation is asynchronous, didFinish might be called even
-        // if the download was cancelled. User cancelled the download,
-        // so we should fail with cancelled error even if the download
-        // actually finished successfully.
-        webkitDownloadCancelled(download);
-        return;
-    }
     if (download->priv->timer)
         g_timer_stop(download->priv->timer.get());
     g_signal_emit(download, signals[FINISHED], 0, nullptr);
@@ -602,7 +594,7 @@ void webkit_download_cancel(WebKitDownload* download)
 
     download->priv->isCancelled = true;
     download->priv->download->cancel([download = Ref { *download->priv->download }] (auto*) {
-        download->client().didFinish(download.get());
+        download->client().legacyDidCancel(download.get());
     });
 }
 

Source/WebKit/UIProcess/API/glib/WebKitDownloadClient.cpp

@@ -93,22 +93,31 @@ class DownloadClient final : public API::DownloadClient {
 
     void didFail(DownloadProxy& downloadProxy, const ResourceError& error, API::Data*) override
     {
+        if (webkitDownloadIsCancelled(m_download.get()))
+            return;
+
         ASSERT(m_download);
-        if (webkitDownloadIsCancelled(m_download.get())) {
-            // Cancellation takes precedence over other errors.
-            webkitDownloadCancelled(m_download.get());
-        } else
-            webkitDownloadFailed(m_download.get(), error);
+        webkitDownloadFailed(m_download.get(), error);
         m_download = nullptr;
     }
 
     void didFinish(DownloadProxy& downloadProxy) override
     {
+        if (webkitDownloadIsCancelled(m_download.get()))
+            return;
+
         ASSERT(m_download);
         webkitDownloadFinished(m_download.get());
         m_download = nullptr;
     }
 
+    void legacyDidCancel(WebKit::DownloadProxy&)
+    {
+        ASSERT(m_download);
+        webkitDownloadCancelled(m_download.get());
+        m_download = nullptr;
+    }
+
     void processDidCrash(DownloadProxy&) override
     {
         m_download = nullptr;