config: Allow None as obsdb, default to it

ols/config.py

@@ -56,7 +56,7 @@ conffile_args = [
     (('-o', '--obsdb'), {
         'dest': 'obsdb',
         'action': 'store',
-        'default': 'observations.db',
+        'default': None,
         'help': 'Location of the observation database file',
     }),
     (('-D', '--datadir'), {

ols/obsdb.py

@@ -9,7 +9,35 @@ from .utils import mcc_mnc_to_opc
 log = logging.getLogger(__name__)
 
 
-class ObservationDB(object):
+class ObservationDBBase(object):
+    """A no-op obsdb. Defines the API and can be used as dummy DB."""
+
+    def __init__(self, filename):
+        pass
+
+    def insert_locate(self, observation):
+        pass
+
+    def insert_submit(self, submission):
+        pass
+
+    def get_observation(self, timestamp):
+        return {
+            'wifis': [],
+            'cells': [],
+        }
+
+    def get_observation_list(self):
+        return []
+
+    def remove(self, timestamp):
+        pass
+
+    def close(self):
+        pass
+
+
+class ObservationDB(ObservationDBBase):
     location_sources = {
         'No location': 0,
         'GNSS': 1,

ols/server.py

@@ -213,7 +213,12 @@ def main():
         raise ValueError(f'Unknown locator type in config: {mtype}')
     log.info(f"Using '{mtype}' locator")
 
-    observationdb = obsdb.ObservationDB(conf['obsdb'])
+    if conf['obsdb'] is None:
+        # Use the dummy obsdb class
+        observationdb = obsdb.ObservationDBBase(None)
+    else:
+        observationdb = obsdb.ObservationDB(conf['obsdb'])
+        log.warning(f"Recording all observations to '{conf['obsdb']}'")
 
     app = web.Application()
     app.add_routes([