marlin-py 0.1.0

Sans-I/O NMEA 0183 + AIS (AIVDM/AIVDO) parser, Rust-backed

marlin-py

Python bindings for the Marlin Rust suite — NMEA 0183 envelope parsing, typed sentence decoding, and AIS (AIVDM/AIVDO) message decoding with multi-sentence reassembly.

Status

Wraps three Rust crates: marlin-nmea-envelope (framing + checksum), marlin-nmea-0183 (GGA, VTG, HDT, PSXN, PRDID typed decoders), and marlin-ais (Types 1/2/3/5/18/19/24A/24B + reassembly). API surface is feature-complete for v0.1. py.typed marker and .pyi stubs ship with the package; mypy --strict is clean across the entire python/marlin/, tests/, and examples/ tree.

Install

The PyPI distribution name is marlin-py; the Python import name stays plain marlin.

# From PyPI (once the v0.1.0 wheels publish)
pip install marlin-py

# Local development — build the extension in-place
cd bindings/python
maturin develop

Quickstart: envelope

from marlin.envelope import StreamingParser

parser = StreamingParser()
parser.feed(b"$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47\r\n")
for sentence in parser:
    talker = sentence.talker.decode() if sentence.talker else ""
    print(talker, sentence.sentence_type, sentence.checksum_ok)
    # GP GGA True

OneShotParser handles UDP datagrams (no \r\n required). parse() is a one-call convenience for a single complete sentence.

Quickstart: NMEA typed decode

from marlin.envelope import parse
from marlin.nmea import Nmea0183Parser, decode_gga, DecodeOptions, PrdidDialect

# Single-sentence convenience.
raw = parse(b"$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47")  # raises EnvelopeError on framing/checksum failure
gga = decode_gga(raw)                # raises DecodeError if not GGA or fields are malformed
print(gga.latitude_deg, gga.longitude_deg, gga.fix_quality)

# Streaming parser — same feed/iterate API as the envelope layer.
parser = Nmea0183Parser.streaming()
parser.feed(b"$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47\r\n")
for msg in parser:
    print(type(msg).__name__, msg)

DecodeOptions configures dialect-sensitive sentences:

opts = DecodeOptions().with_prdid_dialect(PrdidDialect.PITCH_ROLL_HEADING)
parser = Nmea0183Parser.streaming(options=opts)

Per-sentence extension functions (decode_gga, decode_vtg, decode_hdt, decode_psxn, decode_prdid) are public so downstream code can build its own message enum and delegate to Marlin for the standard types.

Quickstart: AIS

from marlin.ais import AisParser, PositionReportA

parser = AisParser.streaming()
parser.feed(b"!AIVDM,1,1,,A,13aGmP0P00PD;88MD5MTDww@2<0L,0*23\r\n")
for msg in parser:
    if isinstance(msg.body, PositionReportA):
        print(msg.body.mmsi, msg.body.latitude_deg, msg.body.longitude_deg)

Multi-sentence reassembly is automatic — feed fragments in order and the parser yields a complete AisMessage only when the last fragment arrives.

AIS clock modes

Fragment reassembly has three timeout behaviours, selected at construction.

No timeout — fragments are buffered until the 16-slot eviction cap is reached. The oldest incomplete group is discarded when a 17th arrives. No clock reads occur:

parser = AisParser.streaming()          # timeout_ms omitted → no timeout

Auto clock — the binding calls time.monotonic_ns() internally to drive the timeout. Use this when system time is reliable and you do not need deterministic replay:

parser = AisParser.streaming(timeout_ms=60_000)          # clock="auto" implied
# or explicitly:
parser = AisParser.streaming(timeout_ms=60_000, clock="auto")

Manual clock — the caller drives the clock via tick(now_ms=...). No clock reads occur inside the binding. This is the correct mode for unit tests, simulators, and any environment where time is patched:

parser = AisParser.streaming(timeout_ms=60_000, clock="manual")

parser.feed(fragment_bytes)
parser.tick(now_ms=current_time_ms)     # expire stale groups at this instant
for msg in parser:
    ...

Calling tick() on a parser that wasn't built with clock="manual" raises ValueError — including parsers built with no timeout_ms (which default to clock="auto").

Errors

Every exception is a MarlinError subclass (importable from marlin):

• EnvelopeError — framing or checksum failure
• DecodeError — field-level decode failure in a typed NMEA sentence
• AisError — AIS armor or bit-level decode failure
• ReassemblyError — fragment reassembly violation (out-of-order, channel mismatch, or timeout eviction)

Property tests (via Hypothesis) verify panic-freedom on arbitrary byte inputs — no input can cause the binding to crash the interpreter.

Examples

Six runnable scripts live in bindings/python/examples/:

Script	What it shows
one_shot_no_crlf.py	Single-datagram framing without \r\n (OneShotParser)
parse_log_file.py	Disk-backed .nmea log replay (StreamingParser)
streaming_tcp_style.py	TCP-style chunked feed; sentences straddle feed() boundaries
decode_aivdm_log.py	Multi-fragment AIS reassembly: Type 1 + Type 5
parse_stdin.py	Stdin pipe reader for live NMEA/AIS capture
live_ais_dashboard.py	Live ship tracker: envelope + AIS in one script, periodic refresh

Type stubs

The py.typed marker is included in the package. Every public class, function, and constant has a .pyi stub. Downstream projects that run mypy --strict get full type-check coverage without extra configuration.

Rust crates

The Python bindings wrap three Rust crates: marlin-nmea-envelope, marlin-nmea-0183, marlin-ais.

MSRV / Python version

Rust 1.82. Python 3.9+.

License

Dual-licensed under MIT OR Apache-2.0.