Improve decoding fractional epoch timestamps

Add `test_timestamp_seconds_float`:

  Publish single reading in JSON format to MQTT broker,
  using a timestamp as Unix Epoch in seconds, as float number.
  Proof that the timestamp is processed and stored correctly.

kotori/daq/storage/influx.py

@@ -1,5 +1,7 @@
 # -*- coding: utf-8 -*-
 # (c) 2015-2021 Andreas Motl <[email protected]>
+import math
+
 import requests
 from copy import deepcopy
 from funcy import project
@@ -177,7 +179,7 @@ def format_chunk(self, meta, data):
                     # Decode timestamp.
                     chunk['time'] = data[time_field]
                     if is_number(chunk['time']):
-                        chunk['time'] = int(float(chunk['time']))
+                        chunk['time'] = float(chunk['time'])
 
                     # Remove timestamp from data payload.
                     del data[time_field]
@@ -209,18 +211,35 @@ def format_chunk(self, meta, data):
             timestamp = chunk['time'] = parse_timestamp(chunk['time'])
 
             # Heuristically compute timestamp precision
-            if isinstance(timestamp, int):
+            if isinstance(timestamp, (int, float)):
                 if timestamp >= 1e17 or timestamp <= -1e17:
                     time_precision = 'n'
                 elif timestamp >= 1e14 or timestamp <= -1e14:
                     time_precision = 'u'
                 elif timestamp >= 1e11 or timestamp <= -1e11:
                     time_precision = 'ms'
 
-                # FIXME: Is this a reasonable default?
+                # TODO: Is this a reasonable default?
                 else:
                     time_precision = 's'
 
+                    # Support fractional epoch timestamps like `1637431069.6585083`.
+                    if isinstance(timestamp, float):
+                        fractional, whole = math.modf(timestamp)
+                        fracdigits = len(str(fractional)) - 2
+                        if fracdigits > 0:
+                            if fracdigits <= 3:
+                                exponent = 3
+                                time_precision = "ms"
+                            elif fracdigits <= 6:
+                                exponent = 6
+                                time_precision = "u"
+                            else:
+                                exponent = 9
+                                time_precision = "n"
+                            timestamp = timestamp * (10 ** exponent)
+
+                chunk['time'] = int(timestamp)
                 chunk['time_precision'] = time_precision
 
             """

test/test_daq_timestamp.py

@@ -35,10 +35,10 @@ def test_timestamp_rfc3339(machinery, create_influxdb, reset_influxdb):
 
 
 @pytest_twisted.inlineCallbacks
-def test_timestamp_seconds(machinery, create_influxdb, reset_influxdb):
+def test_timestamp_seconds_integer(machinery, create_influxdb, reset_influxdb):
     """
     Publish single reading in JSON format to MQTT broker,
-    using a timestamp as Unix Epoch in seconds.
+    using a timestamp as Unix Epoch in seconds, as integer number.
     Proof that the timestamp is processed and stored correctly.
     """
 
@@ -59,6 +59,31 @@ def test_timestamp_seconds(machinery, create_influxdb, reset_influxdb):
     yield record
 
 
+@pytest_twisted.inlineCallbacks
+def test_timestamp_seconds_float(machinery, create_influxdb, reset_influxdb):
+    """
+    Publish single reading in JSON format to MQTT broker,
+    using a timestamp as Unix Epoch in seconds, as float number.
+    Proof that the timestamp is processed and stored correctly.
+    """
+
+    # Submit a single measurement, with timestamp.
+    data = {
+        'temperature': 42.84,
+        'humidity': 83.1,
+        'timestamp': 1637431069.6585083
+    }
+    yield mqtt_json_sensor(settings.mqtt_topic_json, data)
+
+    # Wait for some time to process the message.
+    yield sleep(PROCESS_DELAY_MQTT)
+
+    # Proof that data arrived in InfluxDB.
+    record = influx_sensors.get_first_record()
+    assert record == {u'time': u'2021-11-20T17:57:49.658508Z', u'humidity': 83.1, u'temperature': 42.84}
+    yield record
+
+
 @pytest_twisted.inlineCallbacks
 def test_timestamp_milliseconds(machinery, create_influxdb, reset_influxdb):
     """