p2p/simulations: fix unmarshal of simulations.Node

Making Node.Up field private in 13292ee897
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/network.go

@@ -647,6 +647,25 @@ func (n *Node) MarshalJSON() ([]byte, error) {
 	})
 }
 
+// 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
+	no := struct {
+		Config *adapters.NodeConfig `json:"config,omitempty"`
+		Up     bool                 `json:"up"`
+	}{}
+	if err := json.Unmarshal(raw, &no); err != nil {
+		return err
+	}
+
+	n.SetUp(no.Up)
+	n.Config = no.Config
+	return nil
+}
+
 // Conn represents a connection between two nodes in the network
 type Conn struct {
 	// One is the node which initiated the connection

p2p/simulations/network_test.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"reflect"
 	"strconv"
 	"strings"
 	"testing"
@@ -485,3 +486,100 @@ 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())
+		},
+	)
+}
+
+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",
+		},
+	}
+}