Cannot use download subcmd to download what i seed torrent

I want to announce the torrent to the dht network with the below code, but cannot use `download` subcmd to download magnet. Thanks for any advice.
```golang
package main

import (
"fmt"
"github.com/anacrolix/torrent"
"github.com/anacrolix/torrent/bencode"
"github.com/anacrolix/torrent/metainfo"
"log"
"net/http"
"os"
"path/filepath"
"time"
)

func main() {
cfg := torrent.NewDefaultClientConfig()
cfg.Seed = true
cfg.Debug = true
cfg.NoDefaultPortForwarding = true
cfg.DisableIPv6 = true

cl, err := torrent.NewClient(cfg)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%x\n", cl.PeerID())
defer cl.Close()
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
cl.WriteStatus(w)
})
go http.ListenAndServe(":8080", nil)

filePath := "testdata/docker.png"
totalLength, err := totalLength(filePath)
if err != nil {
log.Fatal(err)
}
pieceLength := metainfo.ChoosePieceLength(totalLength)
info := metainfo.Info{
PieceLength: pieceLength,
}
err = info.BuildFromFilePath(filePath)
if err != nil {
log.Fatal(err)
}
for _, fi := range info.Files {
log.Printf("added %q", fi.Path)
}
mi := &metainfo.MetaInfo{
InfoBytes: bencode.MustMarshal(info),
}
torrentFile = mi
torrentFile.Announce = ""

// Add the torrent to the client
tor, err := cl.AddTorrent(torrentFile)
if err != nil {
log.Fatal(err)
}

// Wait for the torrent to be ready
<-tor.GotInfo()

hash := tor.InfoHash()
fmt.Printf("%v\n", tor.Metainfo().Magnet(&hash, tor.Info()))

// Announce the torrent to DHT
for _, _ds := range cl.DhtServers() {
ds := _ds
done, _, err := tor.AnnounceToDht(ds)
if err != nil {
log.Fatal(err)
}
for c := range done {
fmt.Println("++++++++++++++++++++++++", c)
}
}
select {}
}
```