Post Datastream error

[BWibo]

Hey there, thx for this library, looks promising. I just did some testing and ran into an error when posting a Datastream:

Python 3.8.10
stapy 0.2.4

import  stapy as sta

sta.set_api_url('https://top-secret-frost-server.de/v1.1')

iotid_thing = sta.Post.thing("rpi-new", "Rpi4")
iotid_sensor = sta.Post.sensor("Temperature", "On-Board temperature sensor", "text/html", "https://abc.de")

iotid_datastream = sta.Post.datastream(
  "Rpi-4 temperature",
  "Rpi4 temperature datastream",
  "DegC",
  "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
  iotid_thing, 2, iotid_sensor
)

Posting the Datastream fails with this error:

```text
Traceback (most recent call last):   
  File "main.py", line 8, in <module>
    iotid_datastream = sta.Post.datastream(
  File "/home/bruno/.local/lib/python3.8/site-packages/stapy/sta/post.py", line 32, in datastream
    return Post.entity(Entity.Datastream, **params)
  File "/home/bruno/.local/lib/python3.8/site-packages/stapy/sta/post.py", line 195, in entity
    ent.set_param(**params)
  File "/home/bruno/.local/lib/python3.8/site-packages/stapy/sta/abstract_entity.py", line 50, in set_param
    self.json = self._update_json(self.entry_map, self.json, **data)
  File "/home/bruno/.local/lib/python3.8/site-packages/stapy/sta/abstract_entity.py", line 112, in _update_json
    val_is = cast(dict, val_is)
  File "/home/bruno/.local/lib/python3.8/site-packages/stapy/common/util.py", line 28, in cast
    return switch.get(typ)(value)
  File "/usr/lib/python3.8/json/__init__.py", line 357, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.8/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.8/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Any idea what I am doing wrong? I tired with setting a dict as properties as well.

[zMoooooritz]

Hey, thank you for your feedback!

Indeed the implementation is correct but does obviously not provide sufficient feedback... As to why the last POST did fail.

The STA requires an JSON-Object as unitOfMeasurement (containing three specific entries) therefore the following snippet does create the Datastream as you tried to achieve:

import stapy as sta

sta.set_api_url("https://top-secret-frost-server.de/v1.1")

iotid_obprop = sta.Post.observed_property("Temperature", "Temperature", "Temperature")
iotid_thing = sta.Post.thing("rpi-new", "Rpi4")
iotid_sensor = sta.Post.sensor("Temperature", "On-Board temperature sensor", "text/html", "https://abc.de")
unit = {
    "name": "Degree Celsius",
    "symbol": "degC",
    "definition": "http://www.qudt.org/qudt/owl/1.0.0/unit/Instances.html#DegreeCelsius"
}

iotid_datastream = sta.Post.datastream(
  "Rpi-4 temperature",
  "Rpi4 temperature datastream",
  unit,
  "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
  iotid_thing, iotid_obprop, iotid_sensor
)

For more (advanced) information see the following link

[BWibo]

Ah right, I forgot for a moment that UoM is not just a String in STA. Thx.