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

1 files changed, 77 insertions, 0 deletions

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
+}