func NewNode(ctx context.Context, cfg *BuildCfg) (*IpfsNode, error) {
	if cfg == nil {
		cfg = new(BuildCfg)
	}

	err := cfg.fillDefaults()
	if err != nil {
		return nil, err
	}

	n := &IpfsNode{
		mode:      offlineMode,
		Repo:      cfg.Repo,
		ctx:       ctx,
		Peerstore: peer.NewPeerstore(),
	}
	if cfg.Online {
		n.mode = onlineMode
	}

	// TODO: this is a weird circular-ish dependency, rework it
	n.proc = goprocessctx.WithContextAndTeardown(ctx, n.teardown)

	if err := setupNode(ctx, n, cfg); err != nil {
		n.Close()
		return nil, err
	}

	return n, nil
}

// NewSwarm constructs a Swarm, with a Chan.
func NewSwarm(ctx context.Context, listenAddrs []ma.Multiaddr,
	local peer.ID, peers peer.Peerstore, bwc metrics.Reporter) (*Swarm, error) {

	listenAddrs, err := filterAddrs(listenAddrs)
	if err != nil {
		return nil, err
	}

	s := &Swarm{
		swarm:   ps.NewSwarm(PSTransport),
		local:   local,
		peers:   peers,
		ctx:     ctx,
		dialT:   DialTimeout,
		notifs:  make(map[inet.Notifiee]ps.Notifiee),
		bwc:     bwc,
		Filters: filter.NewFilters(),
	}

	// configure Swarm
	s.proc = goprocessctx.WithContextAndTeardown(ctx, s.teardown)
	s.SetConnHandler(nil) // make sure to setup our own conn handler.

	// setup swarm metrics
	prom.MustRegisterOrGet(peersTotal)
	s.Notify((*metricsNotifiee)(s))

	return s, s.listen(listenAddrs)
}

// newPeernet constructs a new peernet
func newPeernet(ctx context.Context, m *mocknet, k ic.PrivKey,
	a ma.Multiaddr) (*peernet, error) {

	p, err := peer.IDFromPublicKey(k.GetPublic())
	if err != nil {
		return nil, err
	}

	// create our own entirely, so that peers knowledge doesn't get shared
	ps := peer.NewPeerstore()
	ps.AddAddr(p, a, peer.PermanentAddrTTL)
	ps.AddPrivKey(p, k)
	ps.AddPubKey(p, k.GetPublic())

	n := &peernet{
		mocknet: m,
		peer:    p,
		ps:      ps,

		connsByPeer: map[peer.ID]map[*conn]struct{}{},
		connsByLink: map[*link]map[*conn]struct{}{},

		notifs: make(map[inet.Notifiee]struct{}),
	}

	n.proc = goprocessctx.WithContextAndTeardown(ctx, n.teardown)
	return n, nil
}

// TODO refactor so maybeRouter isn't special-cased in this way
func standardWithRouting(r repo.Repo, online bool, routingOption RoutingOption, hostOption HostOption) ConfigOption {
	return func(ctx context.Context) (n *IpfsNode, err error) {
		// FIXME perform node construction in the main constructor so it isn't
		// necessary to perform this teardown in this scope.
		success := false
		defer func() {
			if !success && n != nil {
				n.teardown()
			}
		}()

		// TODO move as much of node initialization as possible into
		// NewIPFSNode. The larger these config options are, the harder it is
		// to test all node construction code paths.

		if r == nil {
			return nil, fmt.Errorf("repo required")
		}
		n = &IpfsNode{
			mode: func() mode {
				if online {
					return onlineMode
				}
				return offlineMode
			}(),
			Repo: r,
		}

		n.ctx = ctx
		n.proc = goprocessctx.WithContextAndTeardown(ctx, n.teardown)

		// setup Peerstore
		n.Peerstore = peer.NewPeerstore()

		// setup local peer ID (private key is loaded in online setup)
		if err := n.loadID(); err != nil {
			return nil, err
		}

		n.Blockstore, err = bstore.WriteCached(bstore.NewBlockstore(n.Repo.Datastore()), kSizeBlockstoreWriteCache)
		if err != nil {
			return nil, err
		}

		if online {
			do := setupDiscoveryOption(n.Repo.Config().Discovery)
			if err := n.startOnlineServices(ctx, routingOption, hostOption, do); err != nil {
				return nil, err
			}
		} else {
			n.Exchange = offline.Exchange(n.Blockstore)
		}

		success = true
		return n, nil
	}
}

func WrapTransportListener(ctx context.Context, ml transport.Listener, local peer.ID, sk ic.PrivKey) (Listener, error) {
	l := &listener{
		Listener: ml,
		local:    local,
		privk:    sk,
	}
	l.proc = goprocessctx.WithContextAndTeardown(ctx, l.teardown)

	log.Debugf("Conn Listener on %s", l.Multiaddr())
	log.Event(ctx, "swarmListen", l)
	return l, nil
}

func NewIPFSNode(ctx context.Context, option ConfigOption) (*IpfsNode, error) {
	node, err := option(ctx)
	if err != nil {
		return nil, err
	}

	if node.ctx == nil {
		node.ctx = ctx
	}
	if node.proc == nil {
		node.proc = goprocessctx.WithContextAndTeardown(node.ctx, node.teardown)
	}

	success := false // flip to true after all sub-system inits succeed
	defer func() {
		if !success {
			node.proc.Close()
		}
	}()

	// Need to make sure it's perfectly clear 1) which variables are expected
	// to be initialized at this point, and 2) which variables will be
	// initialized after this point.

	node.Blocks, err = bserv.New(node.Blockstore, node.Exchange)
	if err != nil {
		return nil, err
	}
	if node.Peerstore == nil {
		node.Peerstore = peer.NewPeerstore()
	}
	node.DAG = merkledag.NewDAGService(node.Blocks)
	node.Pinning, err = pin.LoadPinner(node.Repo.Datastore(), node.DAG)
	if err != nil {
		node.Pinning = pin.NewPinner(node.Repo.Datastore(), node.DAG)
	}
	node.Resolver = &path.Resolver{DAG: node.DAG}

	// Setup the mutable ipns filesystem structure
	if node.OnlineMode() {
		fs, err := ipnsfs.NewFilesystem(ctx, node.DAG, node.Namesys, node.Pinning, node.PrivateKey)
		if err != nil && err != kb.ErrLookupFailure {
			return nil, err
		}
		node.IpnsFs = fs
	}

	success = true
	return node, nil
}

// newPeernet constructs a new peernet
func newPeernet(ctx context.Context, m *mocknet, p peer.ID, ps peer.Peerstore) (*peernet, error) {

	n := &peernet{
		mocknet: m,
		peer:    p,
		ps:      ps,

		connsByPeer: map[peer.ID]map[*conn]struct{}{},
		connsByLink: map[*link]map[*conn]struct{}{},

		notifs: make(map[inet.Notifiee]struct{}),
	}

	n.proc = goprocessctx.WithContextAndTeardown(ctx, n.teardown)
	return n, nil
}

// Listen listens on the particular multiaddr, with given peer and peerstore.
func Listen(ctx context.Context, addr ma.Multiaddr, local peer.ID, sk ic.PrivKey) (Listener, error) {
	ml, err := manetListen(addr)
	if err != nil {
		return nil, err
	}

	l := &listener{
		Listener: ml,
		local:    local,
		privk:    sk,
	}
	l.proc = goprocessctx.WithContextAndTeardown(ctx, l.teardown)

	log.Debugf("Conn Listener on %s", l.Multiaddr())
	log.Event(ctx, "swarmListen", l)
	return l, nil
}

// NewSwarm constructs a Swarm, with a Chan.
func NewSwarm(ctx context.Context, listenAddrs []ma.Multiaddr,
	local peer.ID, peers peer.Peerstore, bwc metrics.Reporter) (*Swarm, error) {

	listenAddrs, err := filterAddrs(listenAddrs)
	if err != nil {
		return nil, err
	}

	wrap := func(c transport.Conn) transport.Conn {
		return mconn.WrapConn(bwc, c)
	}

	s := &Swarm{
		swarm:  ps.NewSwarm(PSTransport),
		local:  local,
		peers:  peers,
		ctx:    ctx,
		dialT:  DialTimeout,
		notifs: make(map[inet.Notifiee]ps.Notifiee),
		transports: []transport.Transport{
			transport.NewTCPTransport(),
			transport.NewUtpTransport(),
		},
		bwc:         bwc,
		fdRateLimit: make(chan struct{}, concurrentFdDials),
		Filters:     filter.NewFilters(),
		dialer:      conn.NewDialer(local, peers.PrivKey(local), wrap),
	}

	// configure Swarm
	s.proc = goprocessctx.WithContextAndTeardown(ctx, s.teardown)
	s.SetConnHandler(nil) // make sure to setup our own conn handler.

	// setup swarm metrics
	prom.MustRegisterOrGet(peersTotal)
	s.Notify((*metricsNotifiee)(s))

	err = s.setupInterfaces(listenAddrs)
	if err != nil {
		return nil, err
	}

	return s, nil
}