Bootstrap DD3 Rust port workspace with host-first compatibility tests

crates/dd3_protocol/src/frame.rs

@@ -0,0 +1,76 @@
+use alloc::vec::Vec;
+
+use crate::crc16_ccitt;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u8)]
+pub enum MsgKind {
+    BatchUp = 0,
+    AckDown = 1,
+}
+
+impl MsgKind {
+    pub fn from_u8(value: u8) -> Option<Self> {
+        match value {
+            0 => Some(Self::BatchUp),
+            1 => Some(Self::AckDown),
+            _ => None,
+        }
+    }
+
+    pub fn as_u8(self) -> u8 {
+        self as u8
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Frame {
+    pub msg_kind: MsgKind,
+    pub short_id: u16,
+    pub payload: Vec<u8>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum FrameDecodeError {
+    LengthMismatch,
+    CrcFail,
+    InvalidMsgKind,
+}
+
+pub fn encode_frame(msg_kind: MsgKind, short_id: u16, payload: &[u8]) -> Vec<u8> {
+    let mut out = Vec::with_capacity(payload.len() + 5);
+    out.push(msg_kind.as_u8());
+    out.extend_from_slice(&short_id.to_be_bytes());
+    out.extend_from_slice(payload);
+    let crc = crc16_ccitt(&out);
+    out.extend_from_slice(&crc.to_be_bytes());
+    out
+}
+
+pub fn decode_frame(frame: &[u8], max_msg_kind: u8) -> Result<Frame, FrameDecodeError> {
+    if frame.len() < 5 {
+        return Err(FrameDecodeError::LengthMismatch);
+    }
+
+    let payload_len = frame.len() - 5;
+    let crc_calc = crc16_ccitt(&frame[..frame.len() - 2]);
+    let crc_rx = u16::from_be_bytes([frame[frame.len() - 2], frame[frame.len() - 1]]);
+    if crc_calc != crc_rx {
+        return Err(FrameDecodeError::CrcFail);
+    }
+
+    let raw_kind = frame[0];
+    if raw_kind > max_msg_kind {
+        return Err(FrameDecodeError::InvalidMsgKind);
+    }
+    let msg_kind = MsgKind::from_u8(raw_kind).ok_or(FrameDecodeError::InvalidMsgKind)?;
+
+    let short_id = u16::from_be_bytes([frame[1], frame[2]]);
+    let payload = frame[3..3 + payload_len].to_vec();
+
+    Ok(Frame {
+        msg_kind,
+        short_id,
+        payload,
+    })
+}