fix(http): wait for the prefetch goroutine to exit before reusing its file (#1606)

* fix(http): wait for the prefetch goroutine to exit before reusing its file

stopPrefetchAndCopyData waited at most 10 s for the Resolve prefetch, but a
stalled body read only times out after readTimeout (15 s). The caller then
closed and removed the temporary file while the prefetch goroutine could
still write to it.

Stopping the prefetch now closes the Resolve body, which interrupts a
pending read, and waits on a channel closed when the goroutine exits. Pause
uses the same path. The stop channel is closed under resolveRespLock so a
concurrent Pause and first-connection takeover cannot close it twice.

The proxy test helper now calls Setup before Resolve, as the downloader
does, so the Resolve request also goes through the proxy.

Fixes #1563

* refactor(http): wait on prefetchExitCh in completeFromResolveFallback

Replaces the 10 ms polling loop with the exit channel added in the
previous commit, so every place that waits for the prefetch uses it.

---------

Co-authored-by: Levi <[email protected]>

internal/protocol/http/fetcher_test.go

@@ -3261,16 +3261,17 @@ func downloadResume(listener net.Listener, connections int, t *testing.T) {
 }
 
 func downloadWithProxy(httpListener net.Listener, proxyListener net.Listener, t *testing.T) {
-	fetcher := downloadReady(httpListener, 4, t)
-	ctl := controller.NewController()
-	ctl.GetProxy = func(requestProxy *base.RequestProxy) func(*gohttp.Request) (*url.URL, error) {
+	// Setup must run before Resolve, as in the downloader, so the Resolve
+	// request also goes through the proxy.
+	f := buildFetcher()
+	f.ctl.GetProxy = func(requestProxy *base.RequestProxy) func(*gohttp.Request) (*url.URL, error) {
 		return (&base.DownloaderProxyConfig{
 			Enable: true,
 			Scheme: "socks5",
 			Host:   proxyListener.Addr().String(),
 		}).ToHandler()
 	}
-	fetcher.Setup(ctl)
+	fetcher := doDownloadReady(f, httpListener, 4, t)
 	err := fetcher.Start()
 	if err != nil {
 		t.Fatal(err)