source routing v2

2026-07-25 03:45:21 +00:00 · 2026-01-07 07:17:44 +07:00
parent 2dd56cbda6
commit aabd0011df
2 changed files with 68 additions and 16 deletions
@@ -240,7 +240,8 @@ object BinaryProtocol {
            if (isCompressed) {
                flags = flags or Flags.IS_COMPRESSED
            }
-            if (!packet.route.isNullOrEmpty()) {
+            // HAS_ROUTE is only supported for v2+ packets
+            if (!packet.route.isNullOrEmpty() && packet.version >= 2u.toUByte()) {
                flags = flags or Flags.HAS_ROUTE
            }
            buffer.put(flags.toByte())
@@ -269,12 +270,14 @@ object BinaryProtocol {
                }
            }

-            // Route (optional): 1 byte count + N*8 bytes
-            packet.route?.let { routeList ->
-                val cleaned = routeList.map { bytes -> bytes.take(SENDER_ID_SIZE).toByteArray().let { if (it.size < SENDER_ID_SIZE) it + ByteArray(SENDER_ID_SIZE - it.size) else it } }
-                val count = cleaned.size.coerceAtMost(255)
-                buffer.put(count.toByte())
-                cleaned.take(count).forEach { hop -> buffer.put(hop) }
+            // Route (optional, v2+ only): 1 byte count + N*8 bytes
+            if (packet.version >= 2u.toUByte()) {
+                packet.route?.let { routeList ->
+                    val cleaned = routeList.map { bytes -> bytes.take(SENDER_ID_SIZE).toByteArray().let { if (it.size < SENDER_ID_SIZE) it + ByteArray(SENDER_ID_SIZE - it.size) else it } }
+                    val count = cleaned.size.coerceAtMost(255)
+                    buffer.put(count.toByte())
+                    cleaned.take(count).forEach { hop -> buffer.put(hop) }
+                }
            }
            
            // Payload (with original size prepended if compressed)
@@ -344,7 +347,8 @@ object BinaryProtocol {
            val hasRecipient = (flags and Flags.HAS_RECIPIENT) != 0u.toUByte()
            val hasSignature = (flags and Flags.HAS_SIGNATURE) != 0u.toUByte()
            val isCompressed = (flags and Flags.IS_COMPRESSED) != 0u.toUByte()
-            val hasRoute = (flags and Flags.HAS_ROUTE) != 0u.toUByte()
+            // HAS_ROUTE is only valid for v2+ packets; ignore the flag for v1
+            val hasRoute = (version >= 2u.toUByte()) && (flags and Flags.HAS_ROUTE) != 0u.toUByte()

            // Payload length - version-dependent (2 or 4 bytes)
            val payloadLength = if (version >= 2u.toUByte()) {
@@ -7,19 +7,66 @@ Status: optional and backward-compatible.
 ## Layering Overview

 - Outer packet: BitChat binary packet with unchanged fixed header (version/type/ttl/timestamp/flags/payloadLength).
- Flags: adds a new bit `HAS_ROUTE (0x08)`.
+- Flags: adds a new bit `HAS_ROUTE (0x08)`. This flag is **only valid for packet version >= 2**.
 - Variable sections (when present, in order):
  1) `SenderID` (8 bytes)
  2) `RecipientID` (8 bytes) if `HAS_RECIPIENT`
-  3) `Route` (if `HAS_ROUTE`): `count` (1 byte) + `count * 8` bytes hop IDs
+  3) `Route` (if `HAS_ROUTE` AND version >= 2): `count` (1 byte) + `count * 8` bytes hop IDs
  4) `Payload` (with optional compression preamble)
  5) `Signature` (64 bytes) if `HAS_SIGNATURE`

-Unknown flags are ignored by older implementations (they will simply not see a route and continue broadcasting as before).
+Unknown flags are ignored by older implementations. For v1 packets, the `HAS_ROUTE` flag MUST be ignored even if set, and the route field MUST NOT be present. This ensures strict backward compatibility.
+
+## Detailed Packet Structure (v1 vs v2)
+
+The Bitchat packet structure is designed to be compact and efficient for BLE transmission.
+
+### Fixed Header
+The fixed header is present in all packets. Its size depends on the version.
+
+| Field | Size (v1) | Size (v2) | Description |
+|---|---|---|---|
+| Version | 1 byte | 1 byte | Protocol version (`0x01` or `0x02`). |
+| Type | 1 byte | 1 byte | Message Type (e.g., `0x01` Announce, `0x02` Message). |
+| TTL | 1 byte | 1 byte | Time-To-Live (hop limit). |
+| Timestamp | 8 bytes | 8 bytes | `UInt64` (big-endian) creation time (ms since epoch). |
+| Flags | 1 byte | 1 byte | Bitmask: `HAS_RECIPIENT(0x01)`, `HAS_SIGNATURE(0x02)`, `IS_COMPRESSED(0x04)`, `HAS_ROUTE(0x08)`. |
+| Payload Length | **2 bytes** | **4 bytes** | `UInt16` (v1) or `UInt32` (v2) length of the *Payload* section only. **Does NOT include route or other headers.** |
+| **Total Header** | **14 bytes** | **16 bytes** | |
+
+### Variable Sections (In Order)
+
+These fields follow the fixed header immediately.
+
+1.  **Sender ID** (Fixed 8 bytes)
+    *   Present in ALL packets.
+    *   Derived from the sender's public key.
+
+2.  **Recipient ID** (Optional, 8 bytes)
+    *   Present only if `HAS_RECIPIENT` flag is set.
+    *   Target peer ID for addressed messages.
+
+3.  **Source Route** (Optional, Variable Length)
+    *   **Condition:** Present **ONLY** if `HAS_ROUTE` flag is set **AND** `Version >= 2`.
+    *   **Structure:**
+        *   `Count` (1 byte): Number of hops (`N`).
+        *   `Hops` (`N * 8` bytes): Sequence of 8-byte Peer IDs.
+    *   **Note:** The size of this field (`1 + 8*N` bytes) is **NOT** included in the `Payload Length` field in the fixed header. It exists structurally between the Recipient ID and the Payload.
+
+4.  **Payload** (Variable Length)
+    *   Size is exactly the value specified in the `Payload Length` field of the fixed header.
+    *   Contains the application data (e.g., encrypted message, announcement TLVs).
+    *   If `IS_COMPRESSED` flag is set, the first 2 bytes are the original uncompressed size (UInt16), followed by the compressed bytes.
+
+5.  **Signature** (Optional, 64 bytes)
+    *   Present only if `HAS_SIGNATURE` flag is set.
+    *   Ed25519 signature covering the entire packet (with TTL=0 and Signature excluded).
+
+---

 ## Route Field Encoding

- Presence: Signaled by the `HAS_ROUTE (0x08)` bit in `flags`.
+- Presence: Signaled by the `HAS_ROUTE (0x08)` bit in `flags` **AND** `version >= 2`.
 - Layout (immediately after optional `RecipientID`):
  - `count`: 1 byte (0..255)
  - `hops`: concatenation of `count` peer IDs, each encoded as exactly 8 bytes
@@ -31,7 +78,7 @@ Unknown flags are ignored by older implementations (they will simply not see a r

 - Applicability: Intended for addressed packets (i.e., where `recipientID` is set and is not the broadcast ID). For broadcast packets, omit the route.
 - Path computation: Use Dijkstra’s shortest path (unit weights) on your internal mesh topology to find a route from the sender (your peerID) to the recipient (the destination peerID). The `BitchatPacket` already contains dedicated `senderID` and `recipientID` fields. The `Route` field's `hops` list **SHOULD** contain the sequence of intermediate peer IDs that the packet should traverse. It **SHOULD NOT** duplicate the `senderID` or `recipientID` if they are already present in the `BitchatPacket`'s dedicated fields. Instead, the `hops` list represents the explicit path *between* the sender and recipient, starting from the first relay and ending with the last relay before the recipient.
- Encoding: Set `HAS_ROUTE`, write `count = path.length`, then the 8‑byte hop IDs in order. Keep `count <= 255`.
+- Encoding: Ensure the packet `version` is set to 2 or higher. Set `HAS_ROUTE`, write `count = path.length`, then the 8‑byte hop IDs in order. Keep `count <= 255`.
 - Signing: The route is covered by the Ed25519 signature (recommended):
  - Signature input is the canonical encoding with `signature` omitted and `ttl = 0` (TTL excluded to allow relay decrement) — same rule as base protocol.

@@ -39,8 +86,8 @@ Unknown flags are ignored by older implementations (they will simply not see a r

 When receiving a packet that is not addressed to you:

-1) If `HAS_ROUTE` is not set, or the route is empty, relay using your normal broadcast logic (subject to TTL/probability policies).
-2) If `HAS_ROUTE` is set:
+1) If `HAS_ROUTE` is not set, or the route is empty, or the packet `version < 2`, relay using your normal broadcast logic (subject to TTL/probability policies).
+2) If `HAS_ROUTE` is set AND `version >= 2`:
   - **Route Sanity Check**: Before processing, the relay **MUST** validate the route. If the route contains duplicate hops (i.e., the same peer ID appears more than once), the packet **MUST** be dropped to prevent loops.
   - If your peer ID appears at index `i` in the hop list:
     - If there is a next hop at `i+1`, attempt a targeted unicast to that next hop if you have a direct connection to it.
@@ -57,7 +104,8 @@ TTL handling remains unchanged: relays decrement TTL by 1 before forwarding (whe

 ## Compatibility

- Omission: If `HAS_ROUTE` is omitted, legacy behavior applies. Relays that don’t implement this feature will ignore the route entirely, because they won’t set or check `HAS_ROUTE`.
+- Omission: If `HAS_ROUTE` is omitted, legacy behavior applies. Relays that don’t implement this feature will ignore the route entirely.
+- Version Constraint: Implementations MUST NOT parse or act on the `Route` field in v1 packets, even if the `HAS_ROUTE` flag is set. This prevents potential parsing ambiguities with legacy clients.
 - Partial support: If any relay on the path cannot directly reach the next hop, it will fall back to broadcast relaying; delivery is still probabilistic like the base protocol.

 ## Minimal Example (conceptual)