p2p, swarm: fix node up races by granular locking (#18976)

* swarm/network: DRY out repeated giga comment

I not necessarily agree with the way we wait for event propagation.
But I truly disagree with having duplicated giga comments.

* p2p/simulations: encapsulate Node.Up field so we avoid data races

The Node.Up field was accessed concurrently without "proper" locking.
There was a lock on Network and that was used sometimes to access
the  field. Other times the locking was missed and we had
a data race.

For example: https://github.com/ethereum/go-ethereum/pull/18464
The case above was solved, but there were still intermittent/hard to
reproduce races. So let's solve the issue permanently.

resolves: ethersphere/go-ethereum#1146

* p2p/simulations: fix unmarshal of simulations.Node

Making Node.Up field private in 13292ee897e345045fbfab3bda23a77589a271c1
broke TestHTTPNetwork and TestHTTPSnapshot. Because the default
UnmarshalJSON does not handle unexported fields.

Important: The fix is partial and not proper to my taste. But I cut
scope as I think the fix may require a change to the current
serialization format. New ticket:
https://github.com/ethersphere/go-ethereum/issues/1177

* p2p/simulations: Add a sanity test case for Node.Config UnmarshalJSON

* p2p/simulations: revert back to defer Unlock() pattern for Network

It's a good patten to call `defer Unlock()` right after `Lock()` so
(new) error cases won't miss to unlock. Let's get back to that pattern.

The patten was abandoned in 85a79b3ad3c5863f8612d25c246bcfad339f36b7,
while fixing a data race. That data race does not exist anymore,
since the Node.Up field got hidden behind its own lock.

* p2p/simulations: consistent naming for test providers Node.UnmarshalJSON

* p2p/simulations: remove JSON annotation from private fields of Node

As unexported fields are not serialized.

* p2p/simulations: fix deadlock in Network.GetRandomDownNode()

Problem: GetRandomDownNode() locks -> getDownNodeIDs() ->
GetNodes() tries to lock -> deadlock

On Network type, unexported functions must assume that `net.lock`
is already acquired and should not call exported functions which
might try to lock again.

* p2p/simulations: ensure method conformity for Network

Connect* methods were moved to p2p/simulations.Network from
swarm/network/simulation. However these new methods did not follow
the pattern of Network methods, i.e., all exported method locks
the whole Network either for read or write.

* p2p/simulations: fix deadlock during network shutdown

`TestDiscoveryPersistenceSimulationSimAdapter` often got into deadlock.
The execution was stuck on two locks, i.e, `Kademlia.lock` and
`p2p/simulations.Network.lock`. Usually the test got stuck once in each
20 executions with high confidence.

`Kademlia` was stuck in `Kademlia.EachAddr()` and `Network` in
`Network.Stop()`.

Solution: in `Network.Stop()` `net.lock` must be released before
calling `node.Stop()` as stopping a node (somehow - I did not find
the exact code path) causes `Network.InitConn()` to be called from
`Kademlia.SuggestPeer()` and that blocks on `net.lock`.

Related ticket: https://github.com/ethersphere/go-ethereum/issues/1223

* swarm/state: simplify if statement in DBStore.Put()

* p2p/simulations: remove faulty godoc from private function

The comment started with the wrong method name.

The method is simple and self explanatory. Also, it's private.
=> Let's just remove the comment.

(cherry picked from commit 50b872bf05b8644f14b9bea340092ced6968dd59)

6 files changed, 290 insertions, 72 deletions

diff --git a/p2p/simulations/connect.go b/p2p/simulations/connect.go
index bb7e7999a..ede96b34c 100644
--- a/p2p/simulations/connect.go
+++ b/p2p/simulations/connect.go
@@ -32,6 +32,9 @@ var (
 // It is useful when constructing a chain network topology
 // when Network adds and removes nodes dynamically.
 func (net *Network) ConnectToLastNode(id enode.ID) (err error) {
+	net.lock.Lock()
+	defer net.lock.Unlock()
+
 	ids := net.getUpNodeIDs()
 	l := len(ids)
 	if l < 2 {
@@ -41,29 +44,35 @@ func (net *Network) ConnectToLastNode(id enode.ID) (err error) {
 	if last == id {
 		last = ids[l-2]
 	}
-	return net.connect(last, id)
+	return net.connectNotConnected(last, id)
 }
 
 // ConnectToRandomNode connects the node with provided NodeID
 // to a random node that is up.
 func (net *Network) ConnectToRandomNode(id enode.ID) (err error) {
-	selected := net.GetRandomUpNode(id)
+	net.lock.Lock()
+	defer net.lock.Unlock()
+
+	selected := net.getRandomUpNode(id)
 	if selected == nil {
 		return ErrNodeNotFound
 	}
-	return net.connect(selected.ID(), id)
+	return net.connectNotConnected(selected.ID(), id)
 }
 
 // ConnectNodesFull connects all nodes one to another.
 // It provides a complete connectivity in the network
 // which should be rarely needed.
 func (net *Network) ConnectNodesFull(ids []enode.ID) (err error) {
+	net.lock.Lock()
+	defer net.lock.Unlock()
+
 	if ids == nil {
 		ids = net.getUpNodeIDs()
 	}
 	for i, lid := range ids {
 		for _, rid := range ids[i+1:] {
-			if err = net.connect(lid, rid); err != nil {
+			if err = net.connectNotConnected(lid, rid); err != nil {
 				return err
 			}
 		}
@@ -74,12 +83,19 @@ func (net *Network) ConnectNodesFull(ids []enode.ID) (err error) {
 // ConnectNodesChain connects all nodes in a chain topology.
 // If ids argument is nil, all nodes that are up will be connected.
 func (net *Network) ConnectNodesChain(ids []enode.ID) (err error) {
+	net.lock.Lock()
+	defer net.lock.Unlock()
+
+	return net.connectNodesChain(ids)
+}
+
+func (net *Network) connectNodesChain(ids []enode.ID) (err error) {
 	if ids == nil {
 		ids = net.getUpNodeIDs()
 	}
 	l := len(ids)
 	for i := 0; i < l-1; i++ {
-		if err := net.connect(ids[i], ids[i+1]); err != nil {
+		if err := net.connectNotConnected(ids[i], ids[i+1]); err != nil {
 			return err
 		}
 	}
@@ -89,6 +105,9 @@ func (net *Network) ConnectNodesChain(ids []enode.ID) (err error) {
 // ConnectNodesRing connects all nodes in a ring topology.
 // If ids argument is nil, all nodes that are up will be connected.
 func (net *Network) ConnectNodesRing(ids []enode.ID) (err error) {
+	net.lock.Lock()
+	defer net.lock.Unlock()
+
 	if ids == nil {
 		ids = net.getUpNodeIDs()
 	}
@@ -96,15 +115,18 @@ func (net *Network) ConnectNodesRing(ids []enode.ID) (err error) {
 	if l < 2 {
 		return nil
 	}
-	if err := net.ConnectNodesChain(ids); err != nil {
+	if err := net.connectNodesChain(ids); err != nil {
 		return err
 	}
-	return net.connect(ids[l-1], ids[0])
+	return net.connectNotConnected(ids[l-1], ids[0])
 }
 
 // ConnectNodesStar connects all nodes into a star topology
 // If ids argument is nil, all nodes that are up will be connected.
 func (net *Network) ConnectNodesStar(ids []enode.ID, center enode.ID) (err error) {
+	net.lock.Lock()
+	defer net.lock.Unlock()
+
 	if ids == nil {
 		ids = net.getUpNodeIDs()
 	}
@@ -112,16 +134,15 @@ func (net *Network) ConnectNodesStar(ids []enode.ID, center enode.ID) (err error
 		if center == id {
 			continue
 		}
-		if err := net.connect(center, id); err != nil {
+		if err := net.connectNotConnected(center, id); err != nil {
 			return err
 		}
 	}
 	return nil
 }
 
-// connect connects two nodes but ignores already connected error.
-func (net *Network) connect(oneID, otherID enode.ID) error {
-	return ignoreAlreadyConnectedErr(net.Connect(oneID, otherID))
+func (net *Network) connectNotConnected(oneID, otherID enode.ID) error {
+	return ignoreAlreadyConnectedErr(net.connect(oneID, otherID))
 }
 
 func ignoreAlreadyConnectedErr(err error) error {
diff --git a/p2p/simulations/events.go b/p2p/simulations/events.go
index 9b2a990e0..984c2e088 100644
--- a/p2p/simulations/events.go
+++ b/p2p/simulations/events.go
@@ -100,7 +100,7 @@ func ControlEvent(v interface{}) *Event {
 func (e *Event) String() string {
 	switch e.Type {
 	case EventTypeNode:
-		return fmt.Sprintf("<node-event> id: %s up: %t", e.Node.ID().TerminalString(), e.Node.Up)
+		return fmt.Sprintf("<node-event> id: %s up: %t", e.Node.ID().TerminalString(), e.Node.Up())
 	case EventTypeConn:
 		return fmt.Sprintf("<conn-event> nodes: %s->%s up: %t", e.Conn.One.TerminalString(), e.Conn.Other.TerminalString(), e.Conn.Up)
 	case EventTypeMsg:
diff --git a/p2p/simulations/http_test.go b/p2p/simulations/http_test.go
index c0a5acb3d..ed43c0ed7 100644
--- a/p2p/simulations/http_test.go
+++ b/p2p/simulations/http_test.go
@@ -421,14 +421,15 @@ type expectEvents struct {
 }
 
 func (t *expectEvents) nodeEvent(id string, up bool) *Event {
+	node := Node{
+		Config: &adapters.NodeConfig{
+			ID: enode.HexID(id),
+		},
+		up: up,
+	}
 	return &Event{
 		Type: EventTypeNode,
-		Node: &Node{
-			Config: &adapters.NodeConfig{
-				ID: enode.HexID(id),
-			},
-			Up: up,
-		},
+		Node: &node,
 	}
 }
 
@@ -480,6 +481,7 @@ loop:
 }
 
 func (t *expectEvents) expect(events ...*Event) {
+	t.Helper()
 	timeout := time.After(10 * time.Second)
 	i := 0
 	for {
@@ -501,8 +503,8 @@ func (t *expectEvents) expect(events ...*Event) {
 				if event.Node.ID() != expected.Node.ID() {
 					t.Fatalf("expected node event %d to have id %q, got %q", i, expected.Node.ID().TerminalString(), event.Node.ID().TerminalString())
 				}
-				if event.Node.Up != expected.Node.Up {
-					t.Fatalf("expected node event %d to have up=%t, got up=%t", i, expected.Node.Up, event.Node.Up)
+				if event.Node.Up() != expected.Node.Up() {
+					t.Fatalf("expected node event %d to have up=%t, got up=%t", i, expected.Node.Up(), event.Node.Up())
 				}
 
 			case EventTypeConn:
diff --git a/p2p/simulations/mocker_test.go b/p2p/simulations/mocker_test.go
index 192be1732..069040257 100644
--- a/p2p/simulations/mocker_test.go
+++ b/p2p/simulations/mocker_test.go
@@ -90,15 +90,12 @@ func TestMocker(t *testing.T) {
 		for {
 			select {
 			case event := <-events:
-				//if the event is a node Up event only
-				if event.Node != nil && event.Node.Up {
+				if isNodeUp(event) {
 					//add the correspondent node ID to the map
 					nodemap[event.Node.Config.ID] = true
 					//this means all nodes got a nodeUp event, so we can continue the test
 					if len(nodemap) == nodeCount {
 						nodesComplete = true
-						//wait for 3s as the mocker will need time to connect the nodes
-						//time.Sleep( 3 *time.Second)
 					}
 				} else if event.Conn != nil && nodesComplete {
 					connCount += 1
@@ -169,3 +166,7 @@ func TestMocker(t *testing.T) {
 		t.Fatalf("Expected empty list of nodes, got: %d", len(nodesInfo))
 	}
 }
+
+func isNodeUp(event *Event) bool {
+	return event.Node != nil && event.Node.Up()
+}
diff --git a/p2p/simulations/network.go b/p2p/simulations/network.go
index a0e621b88..2049a5108 100644
--- a/p2p/simulations/network.go
+++ b/p2p/simulations/network.go
@@ -136,7 +136,7 @@ func (net *Network) Config() *NetworkConfig {
 // StartAll starts all nodes in the network
 func (net *Network) StartAll() error {
 	for _, node := range net.Nodes {
-		if node.Up {
+		if node.Up() {
 			continue
 		}
 		if err := net.Start(node.ID()); err != nil {
@@ -149,7 +149,7 @@ func (net *Network) StartAll() error {
 // StopAll stops all nodes in the network
 func (net *Network) StopAll() error {
 	for _, node := range net.Nodes {
-		if !node.Up {
+		if !node.Up() {
 			continue
 		}
 		if err := net.Stop(node.ID()); err != nil {
@@ -168,27 +168,23 @@ func (net *Network) Start(id enode.ID) error {
 // snapshots
 func (net *Network) startWithSnapshots(id enode.ID, snapshots map[string][]byte) error {
 	net.lock.Lock()
+	defer net.lock.Unlock()
 
 	node := net.getNode(id)
 	if node == nil {
-		net.lock.Unlock()
 		return fmt.Errorf("node %v does not exist", id)
 	}
-	if node.Up {
-		net.lock.Unlock()
+	if node.Up() {
 		return fmt.Errorf("node %v already up", id)
 	}
 	log.Trace("Starting node", "id", id, "adapter", net.nodeAdapter.Name())
 	if err := node.Start(snapshots); err != nil {
-		net.lock.Unlock()
 		log.Warn("Node startup failed", "id", id, "err", err)
 		return err
 	}
-	node.Up = true
+	node.SetUp(true)
 	log.Info("Started node", "id", id)
 	ev := NewEvent(node)
-	net.lock.Unlock()
-
 	net.events.Send(ev)
 
 	// subscribe to peer events
@@ -219,7 +215,7 @@ func (net *Network) watchPeerEvents(id enode.ID, events chan *p2p.PeerEvent, sub
 		if node == nil {
 			return
 		}
-		node.Up = false
+		node.SetUp(false)
 		ev := NewEvent(node)
 		net.events.Send(ev)
 	}()
@@ -257,30 +253,42 @@ func (net *Network) watchPeerEvents(id enode.ID, events chan *p2p.PeerEvent, sub
 
 // Stop stops the node with the given ID
 func (net *Network) Stop(id enode.ID) error {
-	net.lock.Lock()
-	node := net.getNode(id)
-	if node == nil {
-		net.lock.Unlock()
-		return fmt.Errorf("node %v does not exist", id)
-	}
-	if !node.Up {
-		net.lock.Unlock()
-		return fmt.Errorf("node %v already down", id)
+	// IMPORTANT: node.Stop() must NOT be called under net.lock as
+	// node.Reachable() closure has a reference to the network and
+	// calls net.InitConn() what also locks the network. => DEADLOCK
+	// That holds until the following ticket is not resolved:
+
+	var err error
+
+	node, err := func() (*Node, error) {
+		net.lock.Lock()
+		defer net.lock.Unlock()
+
+		node := net.getNode(id)
+		if node == nil {
+			return nil, fmt.Errorf("node %v does not exist", id)
+		}
+		if !node.Up() {
+			return nil, fmt.Errorf("node %v already down", id)
+		}
+		node.SetUp(false)
+		return node, nil
+	}()
+	if err != nil {
+		return err
 	}
-	node.Up = false
-	net.lock.Unlock()
 
-	err := node.Stop()
+	err = node.Stop() // must be called without net.lock
+
+	net.lock.Lock()
+	defer net.lock.Unlock()
+
 	if err != nil {
-		net.lock.Lock()
-		node.Up = true
-		net.lock.Unlock()
+		node.SetUp(true)
 		return err
 	}
 	log.Info("Stopped node", "id", id, "err", err)
-	net.lock.Lock()
 	ev := ControlEvent(node)
-	net.lock.Unlock()
 	net.events.Send(ev)
 	return nil
 }
@@ -288,8 +296,14 @@ func (net *Network) Stop(id enode.ID) error {
 // Connect connects two nodes together by calling the "admin_addPeer" RPC
 // method on the "one" node so that it connects to the "other" node
 func (net *Network) Connect(oneID, otherID enode.ID) error {
+	net.lock.Lock()
+	defer net.lock.Unlock()
+	return net.connect(oneID, otherID)
+}
+
+func (net *Network) connect(oneID, otherID enode.ID) error {
 	log.Debug("Connecting nodes with addPeer", "id", oneID, "other", otherID)
-	conn, err := net.InitConn(oneID, otherID)
+	conn, err := net.initConn(oneID, otherID)
 	if err != nil {
 		return err
 	}
@@ -387,6 +401,14 @@ func (net *Network) GetNode(id enode.ID) *Node {
 	return net.getNode(id)
 }
 
+func (net *Network) getNode(id enode.ID) *Node {
+	i, found := net.nodeMap[id]
+	if !found {
+		return nil
+	}
+	return net.Nodes[i]
+}
+
 // GetNode gets the node with the given name, returning nil if the node does
 // not exist
 func (net *Network) GetNodeByName(name string) *Node {
@@ -409,28 +431,29 @@ func (net *Network) GetNodes() (nodes []*Node) {
 	net.lock.RLock()
 	defer net.lock.RUnlock()
 
-	nodes = append(nodes, net.Nodes...)
-	return nodes
+	return net.getNodes()
 }
 
-func (net *Network) getNode(id enode.ID) *Node {
-	i, found := net.nodeMap[id]
-	if !found {
-		return nil
-	}
-	return net.Nodes[i]
+func (net *Network) getNodes() (nodes []*Node) {
+	nodes = append(nodes, net.Nodes...)
+	return nodes
 }
 
 // GetRandomUpNode returns a random node on the network, which is running.
 func (net *Network) GetRandomUpNode(excludeIDs ...enode.ID) *Node {
 	net.lock.RLock()
 	defer net.lock.RUnlock()
+	return net.getRandomUpNode(excludeIDs...)
+}
+
+// GetRandomUpNode returns a random node on the network, which is running.
+func (net *Network) getRandomUpNode(excludeIDs ...enode.ID) *Node {
 	return net.getRandomNode(net.getUpNodeIDs(), excludeIDs)
 }
 
 func (net *Network) getUpNodeIDs() (ids []enode.ID) {
 	for _, node := range net.Nodes {
-		if node.Up {
+		if node.Up() {
 			ids = append(ids, node.ID())
 		}
 	}
@@ -445,8 +468,8 @@ func (net *Network) GetRandomDownNode(excludeIDs ...enode.ID) *Node {
 }
 
 func (net *Network) getDownNodeIDs() (ids []enode.ID) {
-	for _, node := range net.GetNodes() {
-		if !node.Up {
+	for _, node := range net.getNodes() {
+		if !node.Up() {
 			ids = append(ids, node.ID())
 		}
 	}
@@ -538,6 +561,10 @@ func (net *Network) getConn(oneID, otherID enode.ID) *Conn {
 func (net *Network) InitConn(oneID, otherID enode.ID) (*Conn, error) {
 	net.lock.Lock()
 	defer net.lock.Unlock()
+	return net.initConn(oneID, otherID)
+}
+
+func (net *Network) initConn(oneID, otherID enode.ID) (*Conn, error) {
 	if oneID == otherID {
 		return nil, fmt.Errorf("refusing to connect to self %v", oneID)
 	}
@@ -595,8 +622,21 @@ type Node struct {
 	// Config if the config used to created the node
 	Config *adapters.NodeConfig `json:"config"`
 
-	// Up tracks whether or not the node is running
-	Up bool `json:"up"`
+	// up tracks whether or not the node is running
+	up   bool
+	upMu sync.RWMutex
+}
+
+func (n *Node) Up() bool {
+	n.upMu.RLock()
+	defer n.upMu.RUnlock()
+	return n.up
+}
+
+func (n *Node) SetUp(up bool) {
+	n.upMu.Lock()
+	defer n.upMu.Unlock()
+	n.up = up
 }
 
 // ID returns the ID of the node
@@ -630,10 +670,29 @@ func (n *Node) MarshalJSON() ([]byte, error) {
 	}{
 		Info:   n.NodeInfo(),
 		Config: n.Config,
-		Up:     n.Up,
+		Up:     n.Up(),
 	})
 }
 
+// UnmarshalJSON implements json.Unmarshaler interface so that we don't lose
+// Node.up status. IMPORTANT: The implementation is incomplete; we lose
+// p2p.NodeInfo.
+func (n *Node) UnmarshalJSON(raw []byte) error {
+	// TODO: How should we turn back NodeInfo into n.Node?
+	// Ticket: https://github.com/ethersphere/go-ethereum/issues/1177
+	node := struct {
+		Config *adapters.NodeConfig `json:"config,omitempty"`
+		Up     bool                 `json:"up"`
+	}{}
+	if err := json.Unmarshal(raw, &node); err != nil {
+		return err
+	}
+
+	n.SetUp(node.Up)
+	n.Config = node.Config
+	return nil
+}
+
 // Conn represents a connection between two nodes in the network
 type Conn struct {
 	// One is the node which initiated the connection
@@ -653,10 +712,10 @@ type Conn struct {
 
 // nodesUp returns whether both nodes are currently up
 func (c *Conn) nodesUp() error {
-	if !c.one.Up {
+	if !c.one.Up() {
 		return fmt.Errorf("one %v is not up", c.One)
 	}
-	if !c.other.Up {
+	if !c.other.Up() {
 		return fmt.Errorf("other %v is not up", c.Other)
 	}
 	return nil
@@ -728,7 +787,7 @@ func (net *Network) snapshot(addServices []string, removeServices []string) (*Sn
 	}
 	for i, node := range net.Nodes {
 		snap.Nodes[i] = NodeSnapshot{Node: *node}
-		if !node.Up {
+		if !node.Up() {
 			continue
 		}
 		snapshots, err := node.Snapshots()
@@ -783,7 +842,7 @@ func (net *Network) Load(snap *Snapshot) error {
 		if _, err := net.NewNodeWithConfig(n.Node.Config); err != nil {
 			return err
 		}
-		if !n.Node.Up {
+		if !n.Node.Up() {
 			continue
 		}
 		if err := net.startWithSnapshots(n.Node.Config.ID, n.Snapshots); err != nil {
@@ -855,7 +914,7 @@ func (net *Network) Load(snap *Snapshot) error {
 	// Start connecting.
 	for _, conn := range snap.Conns {
 
-		if !net.GetNode(conn.One).Up || !net.GetNode(conn.Other).Up {
+		if !net.GetNode(conn.One).Up() || !net.GetNode(conn.Other).Up() {
 			//in this case, at least one of the nodes of a connection is not up,
 			//so it would result in the snapshot `Load` to fail
 			continue
@@ -909,7 +968,7 @@ func (net *Network) executeControlEvent(event *Event) {
 }
 
 func (net *Network) executeNodeEvent(e *Event) error {
-	if !e.Node.Up {
+	if !e.Node.Up() {
 		return net.Stop(e.Node.ID())
 	}
 
diff --git a/p2p/simulations/network_test.go b/p2p/simulations/network_test.go
index b7852addb..8b644ffb0 100644
--- a/p2p/simulations/network_test.go
+++ b/p2p/simulations/network_test.go
@@ -20,6 +20,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"reflect"
 	"strconv"
 	"strings"
 	"testing"
@@ -485,3 +486,137 @@ func benchmarkMinimalServiceTmp(b *testing.B) {
 		}
 	}
 }
+
+func TestNode_UnmarshalJSON(t *testing.T) {
+	t.Run(
+		"test unmarshal of Node up field",
+		func(t *testing.T) {
+			runNodeUnmarshalJSON(t, casesNodeUnmarshalJSONUpField())
+		},
+	)
+	t.Run(
+		"test unmarshal of Node Config field",
+		func(t *testing.T) {
+			runNodeUnmarshalJSON(t, casesNodeUnmarshalJSONConfigField())
+		},
+	)
+}
+
+func runNodeUnmarshalJSON(t *testing.T, tests []nodeUnmarshalTestCase) {
+	t.Helper()
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var got Node
+			if err := got.UnmarshalJSON([]byte(tt.marshaled)); err != nil {
+				expectErrorMessageToContain(t, err, tt.wantErr)
+			}
+			expectNodeEquality(t, got, tt.want)
+		})
+	}
+}
+
+type nodeUnmarshalTestCase struct {
+	name      string
+	marshaled string
+	want      Node
+	wantErr   string
+}
+
+func expectErrorMessageToContain(t *testing.T, got error, want string) {
+	t.Helper()
+	if got == nil && want == "" {
+		return
+	}
+
+	if got == nil && want != "" {
+		t.Errorf("error was expected, got: nil, want: %v", want)
+		return
+	}
+
+	if !strings.Contains(got.Error(), want) {
+		t.Errorf(
+			"unexpected error message, got  %v, want: %v",
+			want,
+			got,
+		)
+	}
+}
+
+func expectNodeEquality(t *testing.T, got Node, want Node) {
+	t.Helper()
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("Node.UnmarshalJSON() = %v, want %v", got, want)
+	}
+}
+
+func casesNodeUnmarshalJSONUpField() []nodeUnmarshalTestCase {
+	return []nodeUnmarshalTestCase{
+		{
+			name:      "empty json",
+			marshaled: "{}",
+			want: Node{
+				up: false,
+			},
+		},
+		{
+			name:      "a stopped node",
+			marshaled: "{\"up\": false}",
+			want: Node{
+				up: false,
+			},
+		},
+		{
+			name:      "a running node",
+			marshaled: "{\"up\": true}",
+			want: Node{
+				up: true,
+			},
+		},
+		{
+			name:      "invalid JSON value on valid key",
+			marshaled: "{\"up\": foo}",
+			wantErr:   "invalid character",
+		},
+		{
+			name:      "invalid JSON key and value",
+			marshaled: "{foo: bar}",
+			wantErr:   "invalid character",
+		},
+		{
+			name:      "bool value expected but got something else (string)",
+			marshaled: "{\"up\": \"true\"}",
+			wantErr:   "cannot unmarshal string into Go struct",
+		},
+	}
+}
+
+func casesNodeUnmarshalJSONConfigField() []nodeUnmarshalTestCase {
+	// Don't do a big fuss around testing, as adapters.NodeConfig should
+	// handle it's own serialization. Just do a sanity check.
+	return []nodeUnmarshalTestCase{
+		{
+			name:      "Config field is omitted",
+			marshaled: "{}",
+			want: Node{
+				Config: nil,
+			},
+		},
+		{
+			name:      "Config field is nil",
+			marshaled: "{\"config\": nil}",
+			want: Node{
+				Config: nil,
+			},
+		},
+		{
+			name:      "a non default Config field",
+			marshaled: "{\"config\":{\"name\":\"node_ecdd0\",\"port\":44665}}",
+			want: Node{
+				Config: &adapters.NodeConfig{
+					Name: "node_ecdd0",
+					Port: 44665,
+				},
+			},
+		},
+	}
+}