utils: iso8601: strip fractional seconds (#56)

According to ISO8601 any number of digits is permitted for fractional seconds, the issue is that Python assumes these are microsecond, and will fail if we have more than 6 digits. In the event that we detect more that 6 digits, truncate the fractional part and pass it to datetime. Signed-off-by: Liam Beguin <[email protected]>
sigmf · Apr 12, 2024 · 2410874 · 2410874
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diff --git a/sigmf/utils.py b/sigmf/utils.py
@@ -10,6 +10,7 @@
 from datetime import datetime
 import sys
 import numpy as np
+import re
 
 from . import error
 
@@ -30,6 +31,13 @@ def parse_iso8601_datetime(datestr: str) -> datetime:
     >>> parse_iso8601_datetime("1955-11-05T06:15:00Z")
     datetime.datetime(1955, 11, 5, 6, 15)
     """
+    # provided string exceeds max precision -> truncate to µs
+    match = re.match(r"^(?P<dt>.*)(?P<frac>\.[0-9]{7,})Z$", datestr)
+    if match:
+        md = match.groupdict()
+        length = min(7, len(md["frac"]))
+        datestr = ''.join([md["dt"], md["frac"][:length], "Z"])
+
     try:
         timestamp = datetime.strptime(datestr, '%Y-%m-%dT%H:%M:%S.%fZ')
     except ValueError:

diff --git a/tests/test_utils.py b/tests/test_utils.py
@@ -0,0 +1,19 @@
+from datetime import datetime
+
+import pytest
+
+from sigmf import utils
+
+
+@pytest.mark.parametrize("ts, expected", [
+    ("1955-07-04T05:15:00Z",                datetime(year=1955, month=7,  day=4, hour=5,  minute=15, second=00, microsecond=0)),
+    ("2956-08-05T06:15:12Z",                datetime(year=2956, month=8,  day=5, hour=6,  minute=15, second=12, microsecond=0)),
+    ("3957-09-06T07:15:12.345Z",            datetime(year=3957, month=9,  day=6, hour=7,  minute=15, second=12, microsecond=345000)),
+    ("4958-10-07T08:15:12.0345Z",           datetime(year=4958, month=10, day=7, hour=8,  minute=15, second=12, microsecond=34500)),
+    ("5959-11-08T09:15:12.000000Z",         datetime(year=5959, month=11, day=8, hour=9,  minute=15, second=12, microsecond=0)),
+    ("6960-12-09T10:15:12.123456789123Z",   datetime(year=6960, month=12, day=9, hour=10, minute=15, second=12, microsecond=123456)),
+
+])
+def test_parse_simple_iso8601(ts, expected):
+    dt = utils.parse_iso8601_datetime(ts)
+    assert dt == expected