Merge pull request #375 from mattsains/packet-structure

Create packet_structure.md

docs/packet_structure.md

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+# Packet Structure
+
+| Field    | Size (bytes)                     | Description                                               |
+|----------|----------------------------------|-----------------------------------------------------------|
+| header   | 1                                | Contains routing type, payload type, and payload version. |
+| path_len | 1                                | Length of the path field in bytes.                        |
+| path     | up to 64 (`MAX_PATH_SIZE`)       | Stores the routing path if applicable.                    |
+| payload  | up to 184 (`MAX_PACKET_PAYLOAD`) | The actual data being transmitted.                        |
+
+Note: see the [payloads doc](./payloads.md) for more information about the content of payload.
+
+## Header Breakdown
+
+| Bits  | Mask   | Field           | Description                                   |
+|-------|--------|-----------------|-----------------------------------------------|
+| 0-1   | `0x03` | Route Type      | Flood, Direct, Reserved - see below.          |
+| 2-5   | `0x0F` | Payload Type    | Request, Response, ACK, etc. - see below.     |
+| 6-7   | `0x03` | Payload Version | Versioning of the payload format - see below. |
+
+## Route Type Values
+
+| Value  | Name                   | Description                          |
+|--------|------------------------|--------------------------------------|
+| `0x00` | `ROUTE_TYPE_RESERVED1` | Reserved for future use.             |
+| `0x01` | `ROUTE_TYPE_FLOOD`     | Flood routing mode (builds up path). |
+| `0x02` | `ROUTE_TYPE_DIRECT`    | Direct route (path is supplied).     |
+| `0x03` | `ROUTE_TYPE_RESERVED2` | Reserved for future use.             |
+
+## Payload Type Values
+
+| Value  | Name                      | Description                                   |
+|--------|---------------------------|-----------------------------------------------|
+| `0x00` | `PAYLOAD_TYPE_REQ`        | Request (destination/source hashes + MAC).    |
+| `0x01` | `PAYLOAD_TYPE_RESPONSE`   | Response to REQ or ANON_REQ.                  |
+| `0x02` | `PAYLOAD_TYPE_TXT_MSG`    | Plain text message.                           |
+| `0x03` | `PAYLOAD_TYPE_ACK`        | Acknowledgment.                               |
+| `0x04` | `PAYLOAD_TYPE_ADVERT`     | Node advertisement.                           |
+| `0x05` | `PAYLOAD_TYPE_GRP_TXT`    | Group text message (unverified).              |
+| `0x06` | `PAYLOAD_TYPE_GRP_DATA`   | Group datagram (unverified).                  |
+| `0x07` | `PAYLOAD_TYPE_ANON_REQ`   | Anonymous request.                            |
+| `0x08` | `PAYLOAD_TYPE_PATH`       | Returned path.                                |
+| `0x0F` | `PAYLOAD_TYPE_RAW_CUSTOM` | Custom packet (raw bytes, custom encryption). |
+
+## Payload Version Values
+
+| Value  | Version | Description                                       |
+|--------|---------|---------------------------------------------------|
+| `0x00` | 1       | 1-byte src/dest hashes, 2-byte MAC.               |
+| `0x01` | 2       | Future version (e.g., 2-byte hashes, 4-byte MAC). |
+| `0x02` | 3       | Future version.                                   |
+| `0x03` | 4       | Future version.                                   |