fix(http): skip prefetch wait for restored downloads (#1584)

internal/protocol/http/fetcher.go

@@ -609,7 +609,7 @@ func (f *Fetcher) stopPrefetchAndCopyData() int64 {
 	}
 
 	// Wait for prefetch to finish (with timeout)
-	for i := 0; i < 1000 && !f.prefetchDone.Load(); i++ {
+	for i := 0; f.prefetchStopCh != nil && i < 1000 && !f.prefetchDone.Load(); i++ {
 		time.Sleep(10 * time.Millisecond)
 	}
 

internal/protocol/http/restore_prefetch_test.go

@@ -0,0 +1,79 @@
+package http
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/GopeedLab/gopeed/internal/controller"
+	"github.com/GopeedLab/gopeed/internal/fetcher"
+	"github.com/GopeedLab/gopeed/internal/test"
+	"github.com/GopeedLab/gopeed/pkg/base"
+	fhttp "github.com/GopeedLab/gopeed/pkg/protocol/http"
+)
+
+func TestFetcher_RestoredStartSkipsAbsentPrefetch(t *testing.T) {
+	data := bytes.Repeat([]byte("0123456789abcdef"), 64*1024)
+	var firstRequest atomic.Int64
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		firstRequest.CompareAndSwap(0, time.Now().UnixNano())
+		http.ServeContent(w, r, "restored.bin", time.Time{}, bytes.NewReader(data))
+	}))
+	defer server.Close()
+
+	dir := t.TempDir()
+	size := int64(len(data))
+	half := size / 2
+	file := filepath.Join(dir, "restored.bin")
+	if err := os.WriteFile(file, data[:half], 0600); err != nil {
+		t.Fatal(err)
+	}
+	conn := &connection{ID: 0, Role: rolePrimary, State: connNotStarted, Chunk: newChunk(0, size-1), Downloaded: half}
+	conn.Chunk.Downloaded = half
+	rangeMode := true
+	saved := &fetcherData{Connections: []*connection{conn}, Range: &rangeMode, ResourceSize: &size, FileSize: &size}
+	meta := &fetcher.FetcherMeta{
+		Req:  &base.Request{URL: server.URL + "/restored.bin"},
+		Res:  &base.Resource{Size: size, Range: true, Files: []*base.FileInfo{{Name: "restored.bin", Size: size}}},
+		Opts: &base.Options{Path: dir, Name: "restored.bin", Extra: &fhttp.OptsExtra{Connections: 1}},
+	}
+	fm := new(FetcherManager)
+	_, restore := fm.Restore()
+	f := restore(meta, saved).(*Fetcher)
+	ctl := controller.NewController()
+	ctl.GetConfig = func(v any) {
+		if err := json.Unmarshal([]byte(test.ToJson(fm.DefaultConfig())), v); err != nil {
+			t.Error(err)
+		}
+	}
+	f.Setup(ctl)
+	defer f.Close()
+	started := time.Now()
+	if err := f.Start(); err != nil {
+		t.Fatal(err)
+	}
+	if err := f.Wait(); err != nil {
+		t.Fatal(err)
+	}
+	actual, err := os.ReadFile(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(actual, data) {
+		t.Fatal("restored download differs from the complete server content")
+	}
+	if firstRequest.Load() == 0 {
+		t.Fatal("restored download did not request the remaining content")
+	}
+	delay := time.Duration(firstRequest.Load() - started.UnixNano())
+	t.Logf("first restored request after %s", delay)
+	if delay > 2*time.Second {
+		t.Errorf("restored download waited %s before its first request", delay)
+	}
+}