Support for generating random NodeIDs and deriving Short/Long names (#2)

* Super rough initial subscription to channels and sending node info

* Very ugly hacky FromRadio subscription

* Add more TODOs :weary:

* Add log message before we try to broadcast NodeInfo

* Add basic positioning broadcasting

* demo sending message from consumer

* Use const for BroadcastNodeID

* Config validation and defaults

* Tidy up examples/TODOs

* Tidy up example

* Handle position and devicetelemetry updates

* Fix dodgy merge

* Allow configuring interval for nodeinfo/position seperately

* Make broadcasted position configurable

* Add MQTTProtoTopic constant rather than modifying topic root

* Add Long/Short generation from NodeID

* Mimic Meshtastic source more closely

* Use generated Long/Short when not specified

* Add TestRandomNodeID

* Generate NodeID above the threshold

5 files changed, 155 insertions, 30 deletions

diff --git a/emulated/emulated.go b/emulated/emulated.go
index 7077ee4..2001276 100644
--- a/emulated/emulated.go
+++ b/emulated/emulated.go
@@ -55,12 +55,10 @@ func (c *Config) validate() error {
 		return fmt.Errorf("NodeID is required")
 	}
 	if c.LongName == "" {
-		// TODO: Generate from NodeID
-		return fmt.Errorf("LongName is required")
+		c.LongName = c.NodeID.DefaultLongName()
 	}
 	if c.ShortName == "" {
-		// TODO: Generate from NodeID
-		return fmt.Errorf("ShortName is required")
+		c.ShortName = c.NodeID.DefaultShortName()
 	}
 	if c.Channels == nil {
 		//lint:ignore ST1005 we're referencing an actual field here.
diff --git a/emulated/example/main.go b/emulated/example/main.go
index d0a16e7..1e9b82b 100644
--- a/emulated/example/main.go
+++ b/emulated/example/main.go
@@ -18,11 +18,14 @@ func main() {
 	ctx := context.Background()
 	log.SetLevel(log.DebugLevel)
 
-	myNodeID := meshtastic.NodeID(3735928559)
+	nodeID, err := meshtastic.RandomNodeID()
+	if err != nil {
+		panic(err)
+	}
 	r, err := emulated.NewRadio(emulated.Config{
 		LongName:   "EXAMPLE",
 		ShortName:  "EMPL",
-		NodeID:     myNodeID,
+		NodeID:     nodeID,
 		MQTTClient: &mqtt.DefaultClient,
 		Channels: &pb.ChannelSet{
 			Settings: []*pb.ChannelSettings{
@@ -65,7 +68,7 @@ func main() {
 		err := r.ToRadio(egCtx, &pb.ToRadio{
 			PayloadVariant: &pb.ToRadio_Packet{
 				Packet: &pb.MeshPacket{
-					From: myNodeID.Uint32(),
+					From: nodeID.Uint32(),
 					// This is hard coded to Noah's node ID
 					To: 2437877602,
 					PayloadVariant: &pb.MeshPacket_Decoded{
diff --git a/node_id.go b/node_id.go
new file mode 100644
index 0000000..5e89145
--- /dev/null
+++ b/node_id.go
@@ -0,0 +1,77 @@
+package meshtastic
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"fmt"
+	"math"
+	"math/big"
+)
+
+// NodeID holds the node identifier. This is a uint32 value which uniquely identifies a node within a mesh.
+type NodeID uint32
+
+const (
+	// BroadcastNodeID is the special NodeID used when broadcasting a packet to a channel.
+	BroadcastNodeID NodeID = math.MaxUint32
+	// ReservedNodeIDThreshold is the threshold at which NodeIDs are considered reserved. Random NodeIDs should not
+	// be generated below this threshold.
+	// Source: https://github.com/meshtastic/firmware/blob/d1ea58975755e146457a8345065e4ca357555275/src/mesh/NodeDB.cpp#L461
+	reservedNodeIDThreshold NodeID = 4
+)
+
+// Uint32 returns the underlying uint32 value of the NodeID.
+func (n NodeID) Uint32() uint32 {
+	return uint32(n)
+}
+
+// String converts the NodeID to a hex formatted string.
+// This is typically how NodeIDs are displayed in Meshtastic UIs.
+func (n NodeID) String() string {
+	return fmt.Sprintf("!%08x", uint32(n))
+}
+
+// Bytes converts the NodeID to a byte slice
+func (n NodeID) Bytes() []byte {
+	bytes := make([]byte, 4) // uint32 is 4 bytes
+	binary.BigEndian.PutUint32(bytes, n.Uint32())
+	return bytes
+}
+
+// DefaultLongName returns the default long node name based on the NodeID.
+// Source: https://github.com/meshtastic/firmware/blob/d1ea58975755e146457a8345065e4ca357555275/src/mesh/NodeDB.cpp#L382
+func (n NodeID) DefaultLongName() string {
+	bytes := make([]byte, 4) // uint32 is 4 bytes
+	binary.BigEndian.PutUint32(bytes, n.Uint32())
+	return fmt.Sprintf("Meshtastic %04x", bytes[2:])
+}
+
+// DefaultShortName returns the default short node name based on the NodeID.
+// Last two bytes of the NodeID represented in hex.
+// Source: https://github.com/meshtastic/firmware/blob/d1ea58975755e146457a8345065e4ca357555275/src/mesh/NodeDB.cpp#L382
+func (n NodeID) DefaultShortName() string {
+	bytes := make([]byte, 4) // uint32 is 4 bytes
+	binary.BigEndian.PutUint32(bytes, n.Uint32())
+	return fmt.Sprintf("%04x", bytes[2:])
+}
+
+// RandomNodeID returns a randomised NodeID.
+// It's recommended to call this the first time a node is started and persist the result.
+//
+// Hardware meshtastic nodes first try a NodeID of the last four bytes of the BLE MAC address. If that ID is already in
+// use or invalid, a random NodeID is generated.
+// Source: https://github.com/meshtastic/firmware/blob/d1ea58975755e146457a8345065e4ca357555275/src/mesh/NodeDB.cpp#L466
+func RandomNodeID() (NodeID, error) {
+	// Generates a random uint32 between reservedNodeIDThreshold and math.MaxUint32
+	randomInt, err := rand.Int(
+		rand.Reader,
+		big.NewInt(
+			int64(math.MaxUint32-reservedNodeIDThreshold.Uint32()),
+		),
+	)
+	if err != nil {
+		return NodeID(0), fmt.Errorf("reading entropy: %w", err)
+	}
+	r := uint32(randomInt.Uint64()) + reservedNodeIDThreshold.Uint32()
+	return NodeID(r), nil
+}
diff --git a/node_id_test.go b/node_id_test.go
new file mode 100644
index 0000000..58f367a
--- /dev/null
+++ b/node_id_test.go
@@ -0,0 +1,70 @@
+package meshtastic
+
+import (
+	"bytes"
+	"testing"
+)
+
+const testNodeID = 3735928559
+
+func TestNodeID_Uint32(t *testing.T) {
+	nodeID := NodeID(testNodeID)
+	got := nodeID.Uint32()
+	if got != testNodeID {
+		t.Errorf("expected %v, got %v", testNodeID, got)
+	}
+}
+
+func TestNodeID_Bytes(t *testing.T) {
+	nodeID := NodeID(testNodeID)
+	want := []byte{0xde, 0xad, 0xbe, 0xef}
+	got := nodeID.Bytes()
+	if !bytes.Equal(got, want) {
+		t.Errorf("expected %v, got %v", want, got)
+	}
+}
+
+func TestNodeID_String(t *testing.T) {
+	nodeID := NodeID(testNodeID)
+	want := "!deadbeef"
+	got := nodeID.String()
+	if want != got {
+		t.Errorf("expected %v, got %v", want, got)
+	}
+}
+
+func TestNodeID_DefaultShortName(t *testing.T) {
+	nodeID := NodeID(testNodeID)
+	want := "beef"
+	got := nodeID.DefaultShortName()
+	if want != got {
+		t.Errorf("expected %v, got %v", want, got)
+	}
+}
+
+func TestNodeID_DefaultLongName(t *testing.T) {
+	nodeID := NodeID(testNodeID)
+	want := "Meshtastic beef"
+	got := nodeID.DefaultLongName()
+	if want != got {
+		t.Errorf("expected %v, got %v", want, got)
+	}
+}
+
+// TestRandomNodeID ensures that RandomNodeID generates a valid NodeID and that multiple calls generate different
+// NodeIDs.
+func TestRandomNodeID(t *testing.T) {
+	nodeID1, err := RandomNodeID()
+	if err != nil {
+		t.Errorf("expected no error when generating the first node id, got %v", err)
+	}
+	t.Logf("nodeID1: %s", nodeID1)
+	nodeID2, err := RandomNodeID()
+	if err != nil {
+		t.Errorf("expected no error when generating the second node id, got %v", err)
+	}
+	t.Logf("nodeID2: %s", nodeID2)
+	if nodeID1 == nodeID2 {
+		t.Errorf("expected random node ids to be different, got %s and %s", nodeID1, nodeID2)
+	}
+}
diff --git a/util.go b/util.go
index ef2c61f..f96ca57 100644
--- a/util.go
+++ b/util.go
@@ -2,31 +2,8 @@ package meshtastic
 
 import (
 	pbuf "buf.build/gen/go/meshtastic/protobufs/protocolbuffers/go/meshtastic"
-	"encoding/binary"
-	"fmt"
-	"math"
 )
 
-type NodeID uint32
-
-func (n NodeID) Uint32() uint32 {
-	return uint32(n)
-}
-
-func (n NodeID) String() string {
-	return fmt.Sprintf("!%08x", uint32(n))
-}
-
-// Bytes converts the NodeID to a byte slice
-func (n NodeID) Bytes() []byte {
-	bytes := make([]byte, 4) // uint32 is 4 bytes
-	binary.BigEndian.PutUint32(bytes, n.Uint32())
-	return bytes
-}
-
-// BroadcastNodeID is the special NodeID used when broadcasting a packet to a channel.
-const BroadcastNodeID NodeID = math.MaxUint32
-
 type Node struct {
 	LongName      string
 	ShortName     string