func (s *Server) setDefaults() (err error) {
	if s.id == "" {
		var id [20]byte
		h := crypto.SHA1.New()
		ss, err := os.Hostname()
		if err != nil {
			log.Print(err)
		}
		ss += s.socket.LocalAddr().String()
		h.Write([]byte(ss))
		if b := h.Sum(id[:0:20]); len(b) != 20 {
			panic(len(b))
		}
		if len(id) != 20 {
			panic(len(id))
		}
		publicIP := func() net.IP {
			if s.config.PublicIP != nil {
				return s.config.PublicIP
			} else {
				return missinggo.AddrIP(s.socket.LocalAddr())
			}
		}()
		SecureNodeId(id[:], publicIP)
		s.id = string(id[:])
	}
	s.nodes = make(map[string]*node, maxNodes)
	return
}

func (cl *Client) pieceHashed(t *Torrent, piece int, correct bool) {
	p := &t.pieces[piece]
	if p.EverHashed {
		// Don't score the first time a piece is hashed, it could be an
		// initial check.
		if correct {
			pieceHashedCorrect.Add(1)
		} else {
			log.Printf("%s: piece %d (%x) failed hash", t, piece, p.Hash)
			pieceHashedNotCorrect.Add(1)
		}
	}
	p.EverHashed = true
	touchers := cl.reapPieceTouches(t, piece)
	if correct {
		for _, c := range touchers {
			c.goodPiecesDirtied++
		}
		err := p.Storage().MarkComplete()
		if err != nil {
			log.Printf("%T: error completing piece %d: %s", t.storage, piece, err)
		}
		t.updatePieceCompletion(piece)
	} else if len(touchers) != 0 {
		log.Printf("dropping and banning %d conns that touched piece", len(touchers))
		for _, c := range touchers {
			c.badPiecesDirtied++
			t.cl.banPeerIP(missinggo.AddrIP(c.remoteAddr()))
			t.dropConnection(c)
		}
	}
	cl.pieceChanged(t, piece)
}

func (cl *Client) acceptConnections(l net.Listener, utp bool) {
	for {
		cl.waitAccept()
		conn, err := l.Accept()
		conn = pproffd.WrapNetConn(conn)
		if cl.closed.IsSet() {
			if conn != nil {
				conn.Close()
			}
			return
		}
		if err != nil {
			log.Print(err)
			// I think something harsher should happen here? Our accept
			// routine just fucked off.
			return
		}
		if utp {
			acceptUTP.Add(1)
		} else {
			acceptTCP.Add(1)
		}
		cl.mu.RLock()
		reject := cl.badPeerIPPort(
			missinggo.AddrIP(conn.RemoteAddr()),
			missinggo.AddrPort(conn.RemoteAddr()))
		cl.mu.RUnlock()
		if reject {
			acceptReject.Add(1)
			conn.Close()
			continue
		}
		go cl.incomingConnection(conn, utp)
	}
}

func addClientPeer(t *Torrent, cl *Client) {
	t.AddPeers([]Peer{
		Peer{
			IP:   missinggo.AddrIP(cl.ListenAddr()),
			Port: missinggo.AddrPort(cl.ListenAddr()),
		},
	})
}

func TestClientTransfer(t *testing.T) {
	greetingTempDir, mi := testutil.GreetingTestTorrent()
	defer os.RemoveAll(greetingTempDir)
	cfg := TestingConfig
	cfg.Seed = true
	cfg.DataDir = greetingTempDir
	seeder, err := NewClient(&cfg)
	if err != nil {
		t.Fatal(err)
	}
	defer seeder.Close()
	seeder.AddTorrentSpec(TorrentSpecFromMetaInfo(mi))
	leecherDataDir, err := ioutil.TempDir("", "")
	if err != nil {
		t.Fatal(err)
	}
	defer os.RemoveAll(leecherDataDir)
	// cfg.TorrentDataOpener = func(info *metainfo.Info) (data.Data, error) {
	// 	return blob.TorrentData(info, leecherDataDir), nil
	// }
	blobStore := blob.NewStore(leecherDataDir)
	cfg.TorrentDataOpener = func(info *metainfo.Info) Data {
		return blobStore.OpenTorrent(info)
	}
	leecher, _ := NewClient(&cfg)
	defer leecher.Close()
	leecherGreeting, _, _ := leecher.AddTorrentSpec(func() (ret *TorrentSpec) {
		ret = TorrentSpecFromMetaInfo(mi)
		ret.ChunkSize = 2
		return
	}())
	// TODO: The piece state publishing is kinda jammed in here until I have a
	// more thorough test.
	go func() {
		s := leecherGreeting.pieceStateChanges.Subscribe()
		defer s.Close()
		for i := range s.Values {
			log.Print(i)
		}
		log.Print("finished")
	}()
	leecherGreeting.AddPeers([]Peer{
		Peer{
			IP:   missinggo.AddrIP(seeder.ListenAddr()),
			Port: missinggo.AddrPort(seeder.ListenAddr()),
		},
	})
	r := leecherGreeting.NewReader()
	defer r.Close()
	_greeting, err := ioutil.ReadAll(r)
	if err != nil {
		t.Fatalf("%q %s", string(_greeting), err)
	}
	greeting := string(_greeting)
	if greeting != testutil.GreetingFileContents {
		t.Fatal(":(")
	}
}

func TestServerDefaultNodeIdSecure(t *testing.T) {
	s, err := NewServer(nil)
	if err != nil {
		t.Fatal(err)
	}
	defer s.Close()
	if !NodeIdSecure(s.ID(), missinggo.AddrIP(s.Addr())) {
		t.Fatal("not secure")
	}
}

func TestServerDefaultNodeIdSecure(t *testing.T) {
	s, err := NewServer(&ServerConfig{
		NoDefaultBootstrap: true,
	})
	require.NoError(t, err)
	defer s.Close()
	if !NodeIdSecure(s.ID(), missinggo.AddrIP(s.Addr())) {
		t.Fatal("not secure")
	}
}

func TestDownloadOnDemand(t *testing.T) {
	layout, err := newGreetingLayout()
	require.NoError(t, err)
	defer layout.Destroy()
	seeder, err := torrent.NewClient(&torrent.Config{
		DataDir:         layout.Completed,
		DisableTrackers: true,
		NoDHT:           true,
		ListenAddr:      "localhost:0",
		Seed:            true,
		// Ensure that the metainfo is obtained over the wire, since we added
		// the torrent to the seeder by magnet.
		DisableMetainfoCache: true,
	})
	require.NoError(t, err)
	defer seeder.Close()
	testutil.ExportStatusWriter(seeder, "s")
	_, err = seeder.AddMagnet(fmt.Sprintf("magnet:?xt=urn:btih:%s", layout.Metainfo.Info.Hash.HexString()))
	require.NoError(t, err)
	leecher, err := torrent.NewClient(&torrent.Config{
		DisableTrackers: true,
		NoDHT:           true,
		ListenAddr:      "localhost:0",
		DisableTCP:      true,
		DefaultStorage:  storage.NewMMap(filepath.Join(layout.BaseDir, "download")),
		// This can be used to check if clients can connect to other clients
		// with the same ID.
		// PeerID: seeder.PeerID(),
	})
	require.NoError(t, err)
	testutil.ExportStatusWriter(leecher, "l")
	defer leecher.Close()
	leecherTorrent, _ := leecher.AddTorrent(layout.Metainfo)
	leecherTorrent.AddPeers([]torrent.Peer{
		torrent.Peer{
			IP:   missinggo.AddrIP(seeder.ListenAddr()),
			Port: missinggo.AddrPort(seeder.ListenAddr()),
		},
	})
	fs := New(leecher)
	defer fs.Destroy()
	root, _ := fs.Root()
	node, _ := root.(fusefs.NodeStringLookuper).Lookup(netContext.Background(), "greeting")
	var attr fuse.Attr
	node.Attr(netContext.Background(), &attr)
	size := attr.Size
	resp := &fuse.ReadResponse{
		Data: make([]byte, size),
	}
	node.(fusefs.HandleReader).Read(netContext.Background(), &fuse.ReadRequest{
		Size: int(size),
	}, resp)
	assert.EqualValues(t, testutil.GreetingFileContents, resp.Data)
}

// Writes the node info to its compact binary representation in b. See
// CompactNodeInfoLen.
func (ni *NodeInfo) PutCompact(b []byte) error {
	if n := copy(b[:], ni.ID[:]); n != 20 {
		panic(n)
	}
	ip := missinggo.AddrIP(ni.Addr).To4()
	if len(ip) != 4 {
		return errors.New("expected ipv4 address")
	}
	if n := copy(b[20:], ip); n != 4 {
		panic(n)
	}
	binary.BigEndian.PutUint16(b[24:], uint16(missinggo.AddrPort(ni.Addr)))
	return nil
}

// Add response nodes to node table.
func (s *Server) liftNodes(d Msg) {
	if d.Y != "r" {
		return
	}
	for _, cni := range d.R.Nodes {
		if missinggo.AddrPort(cni.Addr) == 0 {
			// TODO: Why would people even do this?
			continue
		}
		if s.ipBlocked(missinggo.AddrIP(cni.Addr)) {
			continue
		}
		n := s.getNode(cni.Addr, string(cni.ID[:]))
		n.SetIDFromBytes(cni.ID[:])
	}
}

func TestTorrentDroppedDuringResponsiveRead(t *testing.T) {
	seederDataDir, mi := testutil.GreetingTestTorrent()
	defer os.RemoveAll(seederDataDir)
	cfg := TestingConfig
	cfg.Seed = true
	cfg.DataDir = seederDataDir
	seeder, err := NewClient(&cfg)
	require.Nil(t, err)
	defer seeder.Close()
	seeder.AddTorrentSpec(TorrentSpecFromMetaInfo(mi))
	leecherDataDir, err := ioutil.TempDir("", "")
	require.Nil(t, err)
	defer os.RemoveAll(leecherDataDir)
	cfg = TestingConfig
	cfg.DataDir = leecherDataDir
	leecher, err := NewClient(&cfg)
	require.Nil(t, err)
	defer leecher.Close()
	leecherTorrent, _, _ := leecher.AddTorrentSpec(func() (ret *TorrentSpec) {
		ret = TorrentSpecFromMetaInfo(mi)
		ret.ChunkSize = 2
		return
	}())
	leecherTorrent.AddPeers([]Peer{
		Peer{
			IP:   missinggo.AddrIP(seeder.ListenAddr()),
			Port: missinggo.AddrPort(seeder.ListenAddr()),
		},
	})
	reader := leecherTorrent.NewReader()
	defer reader.Close()
	reader.SetReadahead(0)
	reader.SetResponsive()
	b := make([]byte, 2)
	_, err = reader.Seek(3, os.SEEK_SET)
	require.NoError(t, err)
	_, err = io.ReadFull(reader, b)
	assert.Nil(t, err)
	assert.EqualValues(t, "lo", string(b))
	go leecherTorrent.Drop()
	_, err = reader.Seek(11, os.SEEK_SET)
	require.NoError(t, err)
	n, err := reader.Read(b)
	assert.EqualError(t, err, "torrent closed")
	assert.EqualValues(t, 0, n)
}

func TestClientTransfer(t *testing.T) {
	greetingTempDir, mi := testutil.GreetingTestTorrent()
	defer os.RemoveAll(greetingTempDir)
	cfg := TestingConfig
	cfg.Seed = true
	cfg.DataDir = greetingTempDir
	seeder, err := NewClient(&cfg)
	if err != nil {
		t.Fatal(err)
	}
	defer seeder.Close()
	seeder.AddTorrentSpec(TorrentSpecFromMetaInfo(mi))
	leecherDataDir, err := ioutil.TempDir("", "")
	if err != nil {
		t.Fatal(err)
	}
	defer os.RemoveAll(leecherDataDir)
	// cfg.TorrentDataOpener = func(info *metainfo.Info) (data.Data, error) {
	// 	return blob.TorrentData(info, leecherDataDir), nil
	// }
	cfg.TorrentDataOpener = blob.NewStore(leecherDataDir).OpenTorrent
	leecher, _ := NewClient(&cfg)
	defer leecher.Close()
	leecherGreeting, _, _ := leecher.AddTorrentSpec(func() (ret *TorrentSpec) {
		ret = TorrentSpecFromMetaInfo(mi)
		ret.ChunkSize = 2
		return
	}())
	leecherGreeting.AddPeers([]Peer{
		Peer{
			IP:   missinggo.AddrIP(seeder.ListenAddr()),
			Port: missinggo.AddrPort(seeder.ListenAddr()),
		},
	})
	r := leecherGreeting.NewReader()
	defer r.Close()
	_greeting, err := ioutil.ReadAll(r)
	if err != nil {
		t.Fatalf("%q %s", string(_greeting), err)
	}
	greeting := string(_greeting)
	if greeting != testutil.GreetingFileContents {
		t.Fatal(":(")
	}
}

func (s *Server) writeToNode(b []byte, node dHTAddr) (err error) {
	if list := s.ipBlockList; list != nil {
		if r, ok := list.Lookup(missinggo.AddrIP(node.UDPAddr())); ok {
			err = fmt.Errorf("write to %s blocked: %s", node, r.Description)
			return
		}
	}
	n, err := s.socket.WriteTo(b, node.UDPAddr())
	if err != nil {
		err = fmt.Errorf("error writing %d bytes to %s: %#v", len(b), node, err)
		return
	}
	if n != len(b) {
		err = io.ErrShortWrite
		return
	}
	return
}

func connRemoteAddrIP(network, laddr string, dialHost string) net.IP {
	l, err := net.Listen(network, laddr)
	if err != nil {
		panic(err)
	}
	go func() {
		c, err := net.Dial(network, net.JoinHostPort(dialHost, fmt.Sprintf("%d", missinggo.AddrPort(l.Addr()))))
		if err != nil {
			panic(err)
		}
		defer c.Close()
	}()
	c, err := l.Accept()
	if err != nil {
		panic(err)
	}
	defer c.Close()
	ret := missinggo.AddrIP(c.RemoteAddr())
	return ret
}

func TestResponsive(t *testing.T) {
	seederDataDir, mi := testutil.GreetingTestTorrent()
	defer os.RemoveAll(seederDataDir)
	cfg := TestingConfig
	cfg.Seed = true
	cfg.DataDir = seederDataDir
	seeder, err := NewClient(&cfg)
	require.Nil(t, err)
	defer seeder.Close()
	seeder.AddTorrentSpec(TorrentSpecFromMetaInfo(mi))
	leecherDataDir, err := ioutil.TempDir("", "")
	require.Nil(t, err)
	defer os.RemoveAll(leecherDataDir)
	cfg = TestingConfig
	cfg.DataDir = leecherDataDir
	leecher, err := NewClient(&cfg)
	require.Nil(t, err)
	defer leecher.Close()
	leecherTorrent, _, _ := leecher.AddTorrentSpec(func() (ret *TorrentSpec) {
		ret = TorrentSpecFromMetaInfo(mi)
		ret.ChunkSize = 2
		return
	}())
	leecherTorrent.AddPeers([]Peer{
		Peer{
			IP:   missinggo.AddrIP(seeder.ListenAddr()),
			Port: missinggo.AddrPort(seeder.ListenAddr()),
		},
	})
	reader := leecherTorrent.NewReader()
	reader.SetReadahead(0)
	reader.SetResponsive()
	b := make([]byte, 2)
	_, err = reader.ReadAt(b, 3)
	assert.Nil(t, err)
	assert.EqualValues(t, "lo", string(b))
	n, err := reader.ReadAt(b, 11)
	assert.Nil(t, err)
	assert.EqualValues(t, 2, n)
	assert.EqualValues(t, "d\n", string(b))
}

func (s *Server) serve() error {
	var b [0x10000]byte
	for {
		n, addr, err := s.socket.ReadFrom(b[:])
		if err != nil {
			return err
		}
		read.Add(1)
		if n == len(b) {
			logonce.Stderr.Printf("received dht packet exceeds buffer size")
			continue
		}
		s.mu.Lock()
		blocked := s.ipBlocked(missinggo.AddrIP(addr))
		s.mu.Unlock()
		if blocked {
			readBlocked.Add(1)
			continue
		}
		s.processPacket(b[:n], newDHTAddr(addr))
	}
}

func testDownloadCancel(t *testing.T, ps testDownloadCancelParams) {
	greetingTempDir, mi := testutil.GreetingTestTorrent()
	defer os.RemoveAll(greetingTempDir)
	cfg := TestingConfig
	cfg.Seed = true
	cfg.DataDir = greetingTempDir
	seeder, err := NewClient(&cfg)
	require.NoError(t, err)
	defer seeder.Close()
	if ps.ExportClientStatus {
		testutil.ExportStatusWriter(seeder, "s")
	}
	seeder.AddTorrentSpec(TorrentSpecFromMetaInfo(mi))
	leecherDataDir, err := ioutil.TempDir("", "")
	require.NoError(t, err)
	defer os.RemoveAll(leecherDataDir)
	fc, err := filecache.NewCache(leecherDataDir)
	require.NoError(t, err)
	if ps.SetLeecherStorageCapacity {
		fc.SetCapacity(ps.LeecherStorageCapacity)
	}
	cfg.DefaultStorage = storage.NewFileStorePieces(fc.AsFileStore())
	cfg.DataDir = leecherDataDir
	leecher, _ := NewClient(&cfg)
	defer leecher.Close()
	if ps.ExportClientStatus {
		testutil.ExportStatusWriter(leecher, "l")
	}
	leecherGreeting, new, err := leecher.AddTorrentSpec(func() (ret *TorrentSpec) {
		ret = TorrentSpecFromMetaInfo(mi)
		ret.ChunkSize = 2
		return
	}())
	require.NoError(t, err)
	assert.True(t, new)
	psc := leecherGreeting.SubscribePieceStateChanges()
	defer psc.Close()
	leecherGreeting.DownloadAll()
	if ps.Cancel {
		leecherGreeting.CancelPieces(0, leecherGreeting.NumPieces())
	}
	leecherGreeting.AddPeers([]Peer{
		Peer{
			IP:   missinggo.AddrIP(seeder.ListenAddr()),
			Port: missinggo.AddrPort(seeder.ListenAddr()),
		},
	})
	completes := make(map[int]bool, 3)
values:
	for {
		// started := time.Now()
		select {
		case _v := <-psc.Values:
			// log.Print(time.Since(started))
			v := _v.(PieceStateChange)
			completes[v.Index] = v.Complete
		case <-time.After(100 * time.Millisecond):
			break values
		}
	}
	if ps.Cancel {
		assert.EqualValues(t, map[int]bool{0: false, 1: false, 2: false}, completes)
	} else {
		assert.EqualValues(t, map[int]bool{0: true, 1: true, 2: true}, completes)
	}

}

// Check that after completing leeching, a leecher transitions to a seeding
// correctly. Connected in a chain like so: Seeder <-> Leecher <-> LeecherLeecher.
func TestSeedAfterDownloading(t *testing.T) {
	greetingTempDir, mi := testutil.GreetingTestTorrent()
	defer os.RemoveAll(greetingTempDir)
	cfg := TestingConfig
	cfg.Seed = true
	cfg.DataDir = greetingTempDir
	seeder, err := NewClient(&cfg)
	require.NoError(t, err)
	defer seeder.Close()
	testutil.ExportStatusWriter(seeder, "s")
	seeder.AddTorrentSpec(TorrentSpecFromMetaInfo(mi))
	cfg.DataDir, err = ioutil.TempDir("", "")
	require.NoError(t, err)
	defer os.RemoveAll(cfg.DataDir)
	leecher, err := NewClient(&cfg)
	require.NoError(t, err)
	defer leecher.Close()
	testutil.ExportStatusWriter(leecher, "l")
	cfg.Seed = false
	// cfg.TorrentDataOpener = nil
	cfg.DataDir, err = ioutil.TempDir("", "")
	require.NoError(t, err)
	defer os.RemoveAll(cfg.DataDir)
	leecherLeecher, _ := NewClient(&cfg)
	defer leecherLeecher.Close()
	testutil.ExportStatusWriter(leecherLeecher, "ll")
	leecherGreeting, _, _ := leecher.AddTorrentSpec(func() (ret *TorrentSpec) {
		ret = TorrentSpecFromMetaInfo(mi)
		ret.ChunkSize = 2
		return
	}())
	llg, _, _ := leecherLeecher.AddTorrentSpec(func() (ret *TorrentSpec) {
		ret = TorrentSpecFromMetaInfo(mi)
		ret.ChunkSize = 3
		return
	}())
	// Simultaneously DownloadAll in Leecher, and read the contents
	// consecutively in LeecherLeecher. This non-deterministically triggered a
	// case where the leecher wouldn't unchoke the LeecherLeecher.
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		r := llg.NewReader()
		defer r.Close()
		b, err := ioutil.ReadAll(r)
		require.NoError(t, err)
		assert.EqualValues(t, testutil.GreetingFileContents, b)
	}()
	leecherGreeting.AddPeers([]Peer{
		Peer{
			IP:   missinggo.AddrIP(seeder.ListenAddr()),
			Port: missinggo.AddrPort(seeder.ListenAddr()),
		},
		Peer{
			IP:   missinggo.AddrIP(leecherLeecher.ListenAddr()),
			Port: missinggo.AddrPort(leecherLeecher.ListenAddr()),
		},
	})
	wg.Add(1)
	go func() {
		defer wg.Done()
		leecherGreeting.DownloadAll()
		leecher.WaitAll()
	}()
	wg.Wait()
}

func testClientTransfer(t *testing.T, ps testClientTransferParams) {
	greetingTempDir, mi := testutil.GreetingTestTorrent()
	defer os.RemoveAll(greetingTempDir)
	cfg := TestingConfig
	cfg.Seed = true
	if ps.SeederStorage != nil {
		cfg.DefaultStorage = ps.SeederStorage(greetingTempDir)
	} else {
		cfg.DataDir = greetingTempDir
	}
	seeder, err := NewClient(&cfg)
	require.NoError(t, err)
	defer seeder.Close()
	if ps.ExportClientStatus {
		testutil.ExportStatusWriter(seeder, "s")
	}
	_, new, err := seeder.AddTorrentSpec(TorrentSpecFromMetaInfo(mi))
	require.NoError(t, err)
	assert.True(t, new)
	leecherDataDir, err := ioutil.TempDir("", "")
	require.NoError(t, err)
	defer os.RemoveAll(leecherDataDir)
	fc, err := filecache.NewCache(leecherDataDir)
	require.NoError(t, err)
	if ps.SetLeecherStorageCapacity {
		fc.SetCapacity(ps.LeecherStorageCapacity)
	}
	cfg.DefaultStorage = ps.LeecherFileCachePieceStorageFactory(fc)
	leecher, err := NewClient(&cfg)
	require.NoError(t, err)
	defer leecher.Close()
	if ps.ExportClientStatus {
		testutil.ExportStatusWriter(leecher, "l")
	}
	leecherGreeting, new, err := leecher.AddTorrentSpec(func() (ret *TorrentSpec) {
		ret = TorrentSpecFromMetaInfo(mi)
		ret.ChunkSize = 2
		ret.Storage = storage.NewFile(leecherDataDir)
		return
	}())
	require.NoError(t, err)
	assert.True(t, new)
	leecherGreeting.AddPeers([]Peer{
		Peer{
			IP:   missinggo.AddrIP(seeder.ListenAddr()),
			Port: missinggo.AddrPort(seeder.ListenAddr()),
		},
	})
	r := leecherGreeting.NewReader()
	defer r.Close()
	if ps.Responsive {
		r.SetResponsive()
	}
	if ps.SetReadahead {
		r.SetReadahead(ps.Readahead)
	}
	for range iter.N(2) {
		pos, err := r.Seek(0, os.SEEK_SET)
		assert.NoError(t, err)
		assert.EqualValues(t, 0, pos)
		_greeting, err := ioutil.ReadAll(r)
		assert.NoError(t, err)
		assert.EqualValues(t, testutil.GreetingFileContents, _greeting)
	}
}

func newDHTAddr(addr net.Addr) dHTAddr {
	return cachedAddr{addr, addr.String(), missinggo.AddrIP(addr)}
}