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50 changes: 50 additions & 0 deletions docs/packet_structure.md
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# Packet Structure

| Field | Size (bytes) | Description |
|--------------|------------------------|-------------|
| `header` | 1 | Contains routing type, payload type, and payload version. |
| `payload_len` | 2 | Length of the payload in bytes. |
| `path_len` | 2 | Length of the path field in bytes. |
| `path` | `MAX_PATH_SIZE` | Stores the routing path if applicable. |
| `payload` | `MAX_PACKET_PAYLOAD` | The actual data being transmitted. |
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@sevenbitbyte sevenbitbyte Mar 21, 2025

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This is not correct. The actual over the air format is:

Field Size (bytes) Description
header 1 Contains routing type, payload type, and payload version.
path_len 1 (uint8) Length of the path field in bytes.
path MAX_PATH_SIZE Stores the routing path if applicable.
payload MAX_PACKET_PAYLOAD The actual data being transmitted.

See packet serialization here:

https://github.com/ripplebiz/MeshCore/blob/main/src/Packet.cpp#L24-L31


## Header Breakdown

| Bits | Mask | Field | Description |
|-------|---------------|----------------|-------------|
| 0-1 | `0x03` | Route Type | Specifies the routing type (Flood, Direct, Reserved). |
| 2-5 | `0x0F` | Payload Type | Specifies the type of payload (Request, Response, Text, ACK, etc.). |
| 6-7 | `0x03` | Payload Version | Versioning of the payload format. |

## 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 | Name | Description |
|--------|---------------|-------------|
| `0x00` | `PAYLOAD_VER_1` | 1-byte src/dest hashes, 2-byte MAC. |
| `0x01` | `PAYLOAD_VER_2` | Future version (e.g., 2-byte hashes, 4-byte MAC). |
| `0x02` | `PAYLOAD_VER_3` | Future version. |
| `0x03` | `PAYLOAD_VER_4` | Future version. |