Initial commit

src/dsp408/protocol/frame.rs

@@ -0,0 +1,119 @@
+use crate::common::errors::FrameError;
+
+pub fn checksum(payload: &[u8]) -> u8 {
+    let mut cs: u8 = 0x01;
+    for &b in payload {
+        cs ^= b;
+    }
+    cs
+}
+
+pub fn build_frame(cmd: u8, args: &[u8]) -> Vec<u8> {
+    let mut payload_body = Vec::with_capacity(1 + args.len());
+    payload_body.push(cmd);
+    payload_body.extend_from_slice(args);
+
+    let length = payload_body.len() as u8;
+
+    let mut inner = Vec::with_capacity(3 + payload_body.len());
+    inner.push(0x00);
+    inner.push(0x01);
+    inner.push(length);
+    inner.extend_from_slice(&payload_body);
+
+    let cs = checksum(&inner);
+
+    let mut frame = Vec::with_capacity(2 + inner.len() + 3);
+    frame.push(0x10);
+    frame.push(0x02);
+    frame.extend_from_slice(&inner);
+    frame.push(0x10);
+    frame.push(0x03);
+    frame.push(cs);
+    frame
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Frame {
+    pub command: u8,
+    pub payload: Vec<u8>,
+}
+
+pub fn extract_frame(data: &[u8]) -> Result<Frame, FrameError> {
+    if data.len() < 8 {
+        return Err(FrameError::new(format!(
+            "Frame too short: expected at least 8 bytes, got {}",
+            data.len()
+        )));
+    }
+
+    if data[0] != 0x10 || data[1] != 0x02 {
+        return Err(FrameError::new(format!(
+            "Invalid frame header: {:#04x} {:#04x}",
+            data[0], data[1]
+        )));
+    }
+
+    if data[2] == 0x00 {
+        return Err(FrameError::new("Not a response frame"));
+    }
+
+    if data[3] != 0x00 {
+        return Err(FrameError::new(format!(
+            "Invalid device id byte: {:#04x}",
+            data[3]
+        )));
+    }
+
+    let footer = find_footer(data)
+        .ok_or_else(|| FrameError::new("Missing frame footer"))?;
+
+    let expected = checksum(&data[2..footer]);
+    let received = data[data.len() - 1];
+
+    if expected != received {
+        return Err(FrameError::new(format!(
+            "Invalid checksum: expected 0x{:02X}, received 0x{:02X}",
+            expected, received
+        )));
+    }
+
+    Ok(Frame {
+        command: data[5],
+        payload: data[6..footer].to_vec(),
+    })
+}
+
+fn find_footer(data: &[u8]) -> Option<usize> {
+    if data.len() < 2 {
+        return None;
+    }
+    for i in 2..data.len() - 1 {
+        if data[i] == 0x10 && data[i + 1] == 0x03 {
+            return Some(i);
+        }
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn build_then_extract_round_trips() {
+        let cmd = 0x34;
+        let args = [0x01, 0x02, 0x03];
+        let frame = build_frame(cmd, &args);
+
+        let decoded = extract_frame(&frame).unwrap();
+        assert_eq!(decoded.command, cmd);
+        assert_eq!(decoded.payload, vec![0x01, 0x02, 0x03]);
+    }
+
+    #[test]
+    fn too_short_is_an_error() {
+        let err = extract_frame(&[0x10, 0x02, 0x01]).unwrap_err();
+        assert!(err.0.contains("too short"));
+    }
+}