M8-T07: extract reusable P1 parser
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"""Pure, privacy-preserving parser for DSMR and WarmteLink P1 telegrams."""
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from __future__ import annotations
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from dataclasses import dataclass, field as dataclass_field
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from decimal import Decimal, InvalidOperation
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from enum import StrEnum
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import hashlib
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import re
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_OBIS_LINE = re.compile(r"^(?P<code>\d+-\d+:\d+\.\d+\.\d+)(?P<values>(?:\([^)]*\))*)$")
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_NUMBER_WITH_UNIT = re.compile(r"^(?P<number>[+-]?\d+(?:\.\d+)?)(?:\*(?P<unit>.+))?$")
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_CHANNEL_OBIS = re.compile(r"^0-(?P<channel>[1-9]\d*):(24|96)\.")
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_EQUIPMENT_ID_CODES = re.compile(r"^0-(?:0|[1-9]\d*):96\.1\.[01]$")
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class IntegrityStatus(StrEnum):
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"""Whether a frame has a verifiable standard DSMR checksum."""
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VALID = "valid"
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INVALID = "invalid"
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UNVERIFIABLE = "unverifiable"
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class P1ParseError(ValueError):
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"""A parse error whose message never includes telegram contents."""
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@dataclass(frozen=True)
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class ObisField:
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"""One sanitized OBIS line, including values not understood by the parser."""
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code: str
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raw_values: tuple[str, ...]
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value: Decimal | None = None
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unit: str | None = None
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comparison_token: str | None = dataclass_field(default=None, repr=False)
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@dataclass(frozen=True)
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class P1Channel:
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"""Fields associated with one M-Bus channel, without its raw identifier."""
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number: int
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device_type: str | None
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equipment_fingerprint: str | None = dataclass_field(repr=False)
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readings: tuple[ObisField, ...]
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@dataclass(frozen=True)
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class P1Telegram:
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"""A parsed telegram with only sanitized, persistence-safe data."""
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frame_length: int
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integrity: IntegrityStatus
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integrity_reason: str
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timestamp: str | None
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equipment_fingerprint: str | None = dataclass_field(repr=False)
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fields: tuple[ObisField, ...]
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channels: tuple[P1Channel, ...]
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class TelegramFramer:
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"""Incrementally extract newline-terminated variable-length telegrams."""
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def __init__(self) -> None:
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self._buffer = bytearray()
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def feed(self, chunk: bytes) -> list[bytes]:
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"""Append *chunk* and return every complete frame now available."""
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self._buffer.extend(chunk)
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frames: list[bytes] = []
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while (bang := self._buffer.find(b"!")) >= 0:
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newline = self._buffer.find(b"\n", bang)
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if newline < 0:
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break
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standard_start = self._buffer.find(b"/")
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start = standard_start if 0 <= standard_start < bang else 0
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frames.append(bytes(self._buffer[start : newline + 1]))
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del self._buffer[: newline + 1]
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return frames
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def dsmr_crc16(data: bytes) -> int:
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"""Return the DSMR CRC-16 over *data* (normally from ``/`` through ``!``)."""
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crc = 0
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for byte in data:
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crc ^= byte
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for _ in range(8):
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crc = (crc >> 1) ^ 0xA001 if crc & 1 else crc >> 1
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return crc & 0xFFFF
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def parse_telegram(frame: bytes) -> P1Telegram:
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"""Parse one complete frame without retaining raw telegram bytes or IDs."""
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bang = frame.find(b"!")
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if bang < 0:
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raise P1ParseError("telegram has no footer marker")
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body = frame[:bang]
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footer = frame[bang + 1 :].rstrip(b"\r\n")
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integrity, reason = _integrity(frame, bang, footer)
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fields, identifiers = _parse_obis_fields(body)
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timestamp = _field_value(fields, "0-0:1.0.0")
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return P1Telegram(
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frame_length=len(frame),
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integrity=integrity,
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integrity_reason=reason,
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timestamp=timestamp,
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equipment_fingerprint=identifiers.get("0-0:96.1.1"),
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fields=tuple(fields),
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channels=_parse_channels(fields, identifiers),
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)
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def _integrity(frame: bytes, bang: int, footer: bytes) -> tuple[IntegrityStatus, str]:
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if not frame.startswith(b"/"):
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return IntegrityStatus.UNVERIFIABLE, "missing standard DSMR '/' header"
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if len(footer) != 4 or not all(chr(byte) in "0123456789abcdefABCDEF" for byte in footer):
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return IntegrityStatus.UNVERIFIABLE, "footer is not a four-digit hexadecimal CRC"
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expected = int(footer, 16)
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actual = dsmr_crc16(frame[: bang + 1])
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if actual == expected:
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return IntegrityStatus.VALID, "CRC16 verified from '/' through '!'"
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return IntegrityStatus.INVALID, f"CRC16 mismatch: expected {expected:04X}, calculated {actual:04X}"
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def _parse_obis_fields(body: bytes) -> tuple[list[ObisField], dict[str, str]]:
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fields: list[ObisField] = []
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identifiers: dict[str, str] = {}
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for line in body.decode("ascii", errors="replace").splitlines()[1:]:
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match = _OBIS_LINE.fullmatch(line)
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if not match:
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continue
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code = match.group("code")
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raw_values = tuple(re.findall(r"\(([^)]*)\)", match.group("values")))
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if _EQUIPMENT_ID_CODES.fullmatch(code):
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comparison_token = _fingerprint(raw_values[-1]) if raw_values else None
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if comparison_token is not None:
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identifiers[code] = comparison_token
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fields.append(ObisField(code, ("<redacted>",), comparison_token=comparison_token))
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continue
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value, unit = _numeric_value(raw_values)
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fields.append(ObisField(code, raw_values, value, unit))
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return fields, identifiers
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def _fingerprint(identifier: str) -> str:
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"""Hash an identifier locally; callers never receive its original value."""
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return hashlib.sha256(identifier.encode("ascii", errors="replace")).hexdigest()
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def _numeric_value(raw_values: tuple[str, ...]) -> tuple[Decimal | None, str | None]:
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if not raw_values:
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return None, None
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match = _NUMBER_WITH_UNIT.fullmatch(raw_values[-1])
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if not match:
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return None, None
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try:
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return Decimal(match.group("number")), match.group("unit")
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except InvalidOperation:
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return None, None
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def _field_value(fields: list[ObisField], code: str) -> str | None:
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field = next((item for item in fields if item.code == code), None)
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return field.raw_values[-1] if field and field.raw_values else None
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def _parse_channels(fields: list[ObisField], identifiers: dict[str, str]) -> tuple[P1Channel, ...]:
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by_channel: dict[int, list[ObisField]] = {}
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for field in fields:
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match = _CHANNEL_OBIS.match(field.code)
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if match:
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by_channel.setdefault(int(match.group("channel")), []).append(field)
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return tuple(
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P1Channel(
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number=number,
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device_type=_field_value(channel_fields, f"0-{number}:24.1.0"),
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equipment_fingerprint=identifiers.get(f"0-{number}:96.1.0"),
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readings=tuple(
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field
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for field in channel_fields
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if field.code == f"0-{number}:24.2.1" and field.value is not None
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),
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)
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for number, channel_fields in sorted(by_channel.items())
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)
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