Add WebSerial support and align SLCAN parsing behavior

.gitignore

@@ -33,6 +33,7 @@ coverage.xml
 *,cover
 .*mypy.json
 .python-version
+.venv/
 
 .project
 .pydevproject

CHANGELOG.rst

@@ -16,6 +16,8 @@ on top of Cyphal v1.0.
 Due to the significant changes, the new version is published under a different name ``pycyphal2`` to allow coexistence
 with v1 in the same Python environment.
 
+- Add Cyphal/CAN SLCAN media with a browser WebSerial backend.
+
 Changelog v1
 ============
 

noxfile.py

@@ -2,6 +2,7 @@
 
 import shutil
 from pathlib import Path
+
 import nox
 
 nox.options.sessions = ["test", "mypy", "lint", "format"]

src/pycyphal2/__init__.py

@@ -155,7 +155,7 @@ async def main():
 from ._transport import Transport as Transport
 from ._transport import TransportArrival as TransportArrival
 
-__version__ = "2.0.0.dev2"
+__version__ = "2.0.0.dev3"
 
 # pdoc needs __all__ to display re-exported members.
 __all__ = [

src/pycyphal2/can/_media_slcan.py

@@ -0,0 +1,199 @@
+"""
+SLCAN text protocol for CAN media (frame codec + adapter handshake).
+"""
+
+from __future__ import annotations
+
+import logging
+
+from ._interface import Frame
+from ._wire import CAN_EXT_ID_MASK, DLC_TO_LENGTH, MTU_CAN_CLASSIC
+
+_logger = logging.getLogger(__name__)
+
+_CAN_STD_ID_MASK = (1 << 11) - 1
+_CR = 0x0D  # ACK / carriage return
+_LF = 0x0A
+_BEL = 0x07  # NACK / bell
+_MAX_LINE_LENGTH = 256
+_STRIP_CHARS = b" \t\r\n\x07\x03"
+
+_CMD_TERMINATOR = bytes([_CR])
+_CMD_CLOSE = b"C"
+_CMD_OPEN = b"O"
+_CMD_SET_BITRATE_PREFIX = b"S"
+_BITRATE_TO_SPEED_CODE = {
+    1_000_000: 8,
+    800_000: 7,
+    500_000: 6,
+    250_000: 5,
+    125_000: 4,
+    100_000: 3,
+    50_000: 2,
+    20_000: 1,
+    10_000: 0,
+}
+
+
+def encode_frame(identifier: int, data: bytes | bytearray | memoryview) -> bytes:
+    """
+    Encode an extended-ID Classic CAN data frame into one SLCAN ``T`` command line.
+    """
+    if not isinstance(identifier, int) or not (0 <= identifier <= CAN_EXT_ID_MASK):
+        raise ValueError(f"Invalid CAN identifier: {identifier!r}")
+    payload = bytes(data)
+    if len(payload) > MTU_CAN_CLASSIC:
+        raise ValueError(f"Invalid CAN data length: {len(payload)}")
+    return f"T{identifier:08X}{len(payload):1d}{payload.hex().upper()}\r".encode()
+
+
+def encode_deinit() -> bytes:
+    """The close command line. Sent fire-and-forget before purging input to reset the adapter."""
+    return _CMD_CLOSE + _CMD_TERMINATOR
+
+
+def encode_init_sequence(bitrate: int | None) -> list[bytes]:
+    """
+    Command lines to bring the adapter up after deinit+purge: optionally set the bitrate, then open.
+    If ``bitrate`` is None, the bitrate command is skipped, the old configured value (or adapter default) is kept.
+    A bitrate not in the standard speed-code table is sent as-is (some adapters accept raw bitrates, e.g. Zubax).
+    Each returned command line expects an ACK.
+    """
+    out: list[bytes] = []
+    if bitrate is not None:
+        code = _BITRATE_TO_SPEED_CODE.get(bitrate, bitrate)
+        out.append(_CMD_SET_BITRATE_PREFIX + str(code).encode("ascii") + _CMD_TERMINATOR)
+    out.append(_CMD_OPEN + _CMD_TERMINATOR)
+    return out
+
+
+def classify_init_response(chunk: bytes) -> bool | None:
+    """Scan a chunk for the first ACK (True) or NACK (False); return None if neither appears."""
+    for byte in chunk:
+        if byte == _CR:
+            return True
+        if byte == _BEL:
+            return False
+    return None
+
+
+class SLCANParser:
+    """
+    Incremental SLCAN parser.
+    Only data frames are returned. Unsupported or malformed input is silently dropped with debug logging.
+    Adapter-specific suffixes after the payload, such as timestamps or flags, are ignored.
+    """
+
+    def __init__(self) -> None:
+        self._buffer = bytearray()
+        self._discarding = False
+
+    def feed(self, chunk: bytes | bytearray | memoryview) -> list[Frame]:
+        out: list[Frame] = []
+        for byte in bytes(chunk):
+            if byte == _BEL:
+                if self._buffer or self._discarding:
+                    _logger.debug("SLCAN drop adapter error len=%d", len(self._buffer))
+                self._buffer.clear()
+                self._discarding = False
+                continue
+            if byte in (_CR, _LF):
+                if self._discarding:
+                    self._buffer.clear()
+                    self._discarding = False
+                    continue
+                if self._buffer:
+                    frame = _parse_line(bytes(self._buffer))
+                    if frame is not None:
+                        out.append(frame)
+                    self._buffer.clear()
+                continue
+            if self._discarding:
+                continue
+            if len(self._buffer) >= _MAX_LINE_LENGTH:
+                _logger.debug("SLCAN drop overlong line len>%d", _MAX_LINE_LENGTH)
+                self._buffer.clear()
+                self._discarding = True
+                continue
+            self._buffer.append(byte)
+        return out
+
+
+def _parse_line(line: bytes) -> Frame | None:
+    # Based on the original PyUAVCAN/PyDroneCAN implementation.
+    # Strips surrounding whitespace and control characters like BEL/ETX.
+    line = line.strip(_STRIP_CHARS)
+    if not line:
+        return None
+    command = line[:1]
+    if command in (b"T", b"x"):
+        return _parse_data_frame(line, id_length=8, max_payload_length=MTU_CAN_CLASSIC)
+    if command == b"t":
+        return _parse_data_frame(line, id_length=3, max_payload_length=MTU_CAN_CLASSIC)
+    if command == b"D":
+        return _parse_data_frame(line, id_length=8, max_payload_length=64)
+    if command in (b"r", b"R"):
+        _logger.debug("SLCAN drop unsupported frame type cmd=%r", command)
+        return None
+    _logger.debug("SLCAN drop unknown line=%r", line)
+    return None
+
+
+def _parse_data_frame(line: bytes, *, id_length: int, max_payload_length: int) -> Frame | None:
+    header_length = 2 + id_length
+    if len(line) < header_length:
+        _logger.debug("SLCAN drop short data line=%r", line)
+        return None
+    identifier = _parse_hex_int(line[1 : 1 + id_length])
+    dlc = _parse_dlc(line[1 + id_length])
+    if identifier is None or dlc is None:
+        _logger.debug("SLCAN drop malformed data header line=%r", line)
+        return None
+    payload_length = DLC_TO_LENGTH[dlc]  # _parse_dlc guarantees dlc in [0, 15]
+    if payload_length > max_payload_length:
+        _logger.debug("SLCAN drop data dlc out of range dlc=%d max=%d line=%r", dlc, max_payload_length, line)
+        return None
+    expected = header_length + payload_length * 2
+    if len(line) < expected:
+        _logger.debug("SLCAN drop data dlc mismatch len=%d expected=%d", len(line), expected)
+        return None
+    if id_length == 3 and identifier > _CAN_STD_ID_MASK:
+        _logger.debug("SLCAN drop invalid standard id=%x", identifier)
+        return None
+    data = _parse_hex_bytes(line[header_length:expected])
+    if data is None:
+        _logger.debug("SLCAN drop malformed data id=%08x", identifier)
+        return None
+    try:
+        return Frame(id=identifier, data=data)
+    except ValueError as ex:
+        _logger.debug("SLCAN drop invalid frame: %s", ex)
+        return None
+
+
+def _parse_hex_int(value: bytes) -> int | None:
+    if not value:
+        return None
+    try:
+        return int(value, 16)
+    except ValueError:
+        return None
+
+
+def _parse_hex_bytes(value: bytes) -> bytes | None:
+    if len(value) % 2 != 0:
+        return None
+    try:
+        return bytes.fromhex(value.decode("ascii"))
+    except (UnicodeDecodeError, ValueError):
+        return None
+
+
+def _parse_dlc(value: int) -> int | None:
+    if ord("0") <= value <= ord("9"):
+        return value - ord("0")
+    if ord("A") <= value <= ord("F"):
+        return 10 + value - ord("A")
+    if ord("a") <= value <= ord("f"):
+        return 10 + value - ord("a")
+    return None