func (t *Transport) SendSnapshot(m snap.Message) {
	p := t.peers[types.ID(m.To)]
	if p == nil {
		m.CloseWithError(errMemberNotFound)
		return
	}
	p.sendSnap(m)
}

func (s *snapshotSender) send(merged snap.Message) {
	m := merged.Message

	start := time.Now()

	body := createSnapBody(merged)
	defer body.Close()

	u := s.picker.pick()
	req := createPostRequest(u, RaftSnapshotPrefix, body, "application/octet-stream", s.tr.URLs, s.from, s.cid)

	plog.Infof("start to send database snapshot [index: %d, to %s]...", m.Snapshot.Metadata.Index, types.ID(m.To))

	err := s.post(req)
	defer merged.CloseWithError(err)
	if err != nil {
		plog.Warningf("database snapshot [index: %d, to: %s] failed to be sent out (%v)", m.Snapshot.Metadata.Index, types.ID(m.To), err)

		// errMemberRemoved is a critical error since a removed member should
		// always be stopped. So we use reportCriticalError to report it to errorc.
		if err == errMemberRemoved {
			reportCriticalError(err, s.errorc)
		}

		s.picker.unreachable(u)
		reportSentFailure(sendSnap, m)
		s.status.deactivate(failureType{source: sendSnap, action: "post"}, err.Error())
		s.r.ReportUnreachable(m.To)
		// report SnapshotFailure to raft state machine. After raft state
		// machine knows about it, it would pause a while and retry sending
		// new snapshot message.
		s.r.ReportSnapshot(m.To, raft.SnapshotFailure)
		return
	}
	reportSentDuration(sendSnap, m, time.Since(start))
	s.status.activate()
	s.r.ReportSnapshot(m.To, raft.SnapshotFinish)
	plog.Infof("database snapshot [index: %d, to: %s] sent out successfully", m.Snapshot.Metadata.Index, types.ID(m.To))
}

func (s *EtcdServer) sendMergedSnap(merged snap.Message) {
	atomic.AddInt64(&s.inflightSnapshots, 1)

	s.r.transport.SendSnapshot(merged)
	go func() {
		select {
		case ok := <-merged.CloseNotify():
			// delay releasing inflight snapshot for another 30 seconds to
			// block log compaction.
			// If the follower still fails to catch up, it is probably just too slow
			// to catch up. We cannot avoid the snapshot cycle anyway.
			if ok {
				select {
				case <-time.After(releaseDelayAfterSnapshot):
				case <-s.done:
				}
			}
			atomic.AddInt64(&s.inflightSnapshots, -1)
		case <-s.done:
			return
		}
	}()
}

func testSnapshotSend(t *testing.T, sm *snap.Message) (bool, []os.FileInfo) {
	d, err := ioutil.TempDir(os.TempDir(), "snapdir")
	if err != nil {
		t.Fatal(err)
	}
	defer os.RemoveAll(d)

	r := &fakeRaft{}
	tr := &Transport{pipelineRt: &http.Transport{}, ClusterID: types.ID(1), Raft: r}
	ch := make(chan struct{}, 1)
	h := &syncHandler{newSnapshotHandler(tr, r, snap.New(d), types.ID(1)), ch}
	srv := httptest.NewServer(h)
	defer srv.Close()

	picker := mustNewURLPicker(t, []string{srv.URL})
	snapsend := newSnapshotSender(tr, picker, types.ID(1), newPeerStatus(types.ID(1)))
	defer snapsend.stop()

	snapsend.send(*sm)

	sent := false
	select {
	case <-time.After(time.Second):
		t.Fatalf("timed out sending snapshot")
	case sent = <-sm.CloseNotify():
	}

	// wait for handler to finish accepting snapshot
	<-ch

	files, rerr := ioutil.ReadDir(d)
	if rerr != nil {
		t.Fatal(rerr)
	}
	return sent, files
}

func (s *snapTransporter) SendSnapshot(m snap.Message) {
	ss := snap.New(s.snapDir)
	ss.SaveDBFrom(m.ReadCloser, m.Snapshot.Metadata.Index+1)
	m.CloseWithError(nil)
	s.snapDoneC <- m
}