Baichuan message header coder.

Every Baichuan message starts with a little-endian header. Its length depends on the message class: the two MODERN_WITH_OFFSET classes carry a trailing payload offset and are 24 bytes, every other class is 20 bytes.

offset  size  field
0       4     magic f0 de bc 0a
4       4     cmdId          u32le
8       4     bodyLength     u32le
12      1     channelId      u8     0/251 push, 1-100 channel + 1, 250 host
13      3     messageId      u24le
16      2     status         u16le  24-byte classes: status code
              encryption            20-byte classes: encryption marker
18      2     messageClass   u16be
20      4     payloadOffset  u32le  24-byte classes only

Examples

Encode and decode the nonce request header

import { assertEquals } from "@std/assert";
import { decode, encode } from "@hertzg/binstruct";
import {
  BAICHUAN_MESSAGE_CLASS,
  baichuanHeader,
} from "@hertzg/reolink-api/encoding/header";

const header = {
  cmdId: 1,
  bodyLength: 0,
  channelId: 250,
  messageId: 1,
  encryption: 0xdc12,
  messageClass: BAICHUAN_MESSAGE_CLASS.LEGACY,
};

const bytes = encode(baichuanHeader(), header);

assertEquals(bytes.length, 20);
assertEquals(decode(baichuanHeader(), bytes), header);

Functions

f
headerLength(messageClass: number): 20 | 24

Returns the header length in bytes for a message class.

Type Aliases

Variables

v
BAICHUAN_MAGIC: 180150000

The four bytes f0 de bc 0a that open every message, read as u32le.

v
BAICHUAN_MESSAGE_CLASS: { LEGACY: number; MODERN: number; MODERN_WITH_OFFSET: number; MODERN_WITH_OFFSET_ALT: number; }

Message classes (bytes 18-19, read as u16be). The class decides the header length, see headerLength.

Usage

import * as mod from "encoding/header.ts";