Protocol layer: XML index, codec, safety tiers, expectations

Parse Parrot's common.xml and ardrone3.xml into CommandSpec objects rather
than transcribing 264 commands by hand. Direction is derived from
comment result=/triggered= with a class-name-suffix fallback for the 31
commands that state neither, giving 101 to-drone and 163 from-drone.
ardrone3.Piloting.FlatTrim is injected: the firmware accepts it but neither
the vendored snapshot nor upstream defines it.

codec encodes the <BBH header (the command id is 16 bits, not 8) and reads
enums as i32 and strings as NUL-terminated, both of which pyparrot gets
wrong. safety assigns the arming tier by class, with Mavlink and Calibration
counted as motion because they move the aircraft. expectations parses the
undocumented #p-c-m grammar including | alternatives and this.<arg> echoes.

90 tests, counts asserted so a bad parse fails loudly.

tests/test_safety.py

@@ -0,0 +1,131 @@
+"""Tiering decides what needs arming, so a misfiled command is a safety bug."""
+
+import collections
+
+from mcbebop.protocol import xml_index
+from mcbebop.protocol.safety import ALWAYS_ALLOWED, tier_for
+from mcbebop.protocol.types import Direction, Tier
+
+MOTION = {
+    # The aircraft itself.
+    "ardrone3.Piloting.FlatTrim",
+    "ardrone3.Piloting.TakeOff",
+    "ardrone3.Piloting.PCMD",
+    "ardrone3.Piloting.Landing",
+    "ardrone3.Piloting.Emergency",
+    "ardrone3.Piloting.NavigateHome",
+    "ardrone3.Piloting.AutoTakeOffMode",
+    "ardrone3.Piloting.moveBy",
+    "ardrone3.Piloting.UserTakeOff",
+    "ardrone3.Piloting.Circle",
+    "ardrone3.Piloting.moveTo",
+    "ardrone3.Piloting.CancelMoveTo",
+    "ardrone3.Piloting.StartPilotedPOI",
+    "ardrone3.Piloting.StopPilotedPOI",
+    "ardrone3.Piloting.CancelMoveBy",
+    "ardrone3.Piloting.StartPilotedPOIV2",
+    "ardrone3.Animations.Flip",
+    # Running a stored flight plan moves the whole mission.
+    "common.Mavlink.Start",
+    "common.Mavlink.Pause",
+    "common.Mavlink.Stop",
+    # Calibration asks a powered aircraft to rotate.
+    "common.Calibration.MagnetoCalibration",
+    "common.Calibration.PitotCalibration",
+    "common.Animations.StartAnimation",
+    "common.Animations.StopAnimation",
+    "common.Animations.StopAllAnimations",
+}
+
+
+def test_motion_set_is_exactly_these():
+    tiered = {c.full_name for c in xml_index.all_commands() if c.tier is Tier.MOTION}
+    assert tiered == MOTION
+
+
+def test_every_motion_command_is_sendable():
+    for name in MOTION:
+        command = xml_index.get(name)
+        assert command is not None, name
+        assert command.direction is Direction.TO_DRONE, name
+
+
+def test_observe_is_the_two_dump_everything_commands():
+    sendable_observe = {
+        c.full_name
+        for c in xml_index.all_commands()
+        if c.tier is Tier.OBSERVE and c.direction is Direction.TO_DRONE
+    }
+    assert sendable_observe == {"common.Common.AllStates", "common.Settings.AllSettings"}
+
+
+def test_envelope_covers_the_limit_and_radio_classes():
+    envelope = {c.full_name for c in xml_index.all_commands() if c.tier is Tier.ENVELOPE}
+    for name in (
+        "ardrone3.PilotingSettings.MaxAltitude",
+        "ardrone3.PilotingSettings.NoFlyOverMaxDistance",
+        "ardrone3.SpeedSettings.MaxVerticalSpeed",
+        "ardrone3.GPSSettings.SetHome",
+        "ardrone3.Network.WifiScan",
+        "ardrone3.NetworkSettings.WifiSelection",
+        "common.Network.Disconnect",
+        "common.WifiSettings.OutdoorSetting",
+        "common.FlightPlanSettings.ReturnHomeOnDisconnect",
+        "common.Settings.Country",
+        "common.Settings.AutoCountry",
+        "common.Settings.Reset",
+        "common.Common.Reboot",
+        "common.Factory.Reset",
+        "common.OverHeat.SwitchOff",
+        "common.Charger.SetMaxChargeRate",
+        "common.Controller.isPiloting",
+    ):
+        assert name in envelope, name
+    assert len(envelope) == 44
+
+
+def test_config_is_the_harmless_remainder():
+    config = {c.full_name for c in xml_index.all_commands() if c.tier is Tier.CONFIG}
+    assert len(config) == 31
+    for name in (
+        "ardrone3.MediaRecord.Picture",
+        "ardrone3.MediaStreaming.VideoEnable",
+        "ardrone3.PictureSettings.VideoFramerate",
+        "ardrone3.Camera.Orientation",
+        "common.Common.CurrentDate",
+        "common.Settings.ProductName",
+        "common.Headlights.intensity",
+    ):
+        assert name in config, name
+    assert not any(
+        c.direction is Direction.FROM_DRONE for c in xml_index.all_commands() if c.tier is Tier.CONFIG
+    )
+
+
+def test_sendable_tiers_account_for_every_to_drone_command():
+    counts = collections.Counter(
+        c.tier for c in xml_index.all_commands() if c.direction is Direction.TO_DRONE
+    )
+    assert counts[Tier.MOTION] == 25
+    assert counts[Tier.ENVELOPE] == 44
+    assert counts[Tier.OBSERVE] == 2
+    assert counts[Tier.CONFIG] == 31
+    assert sum(counts.values()) == 102  # 101 in the XML plus the injected FlatTrim
+
+
+def test_events_are_observe():
+    for command in xml_index.all_commands():
+        if command.direction is Direction.FROM_DRONE:
+            assert command.tier is Tier.OBSERVE, command.full_name
+
+
+def test_always_allowed_are_the_two_that_end_a_flight():
+    assert frozenset({"ardrone3.Piloting.Landing", "ardrone3.Piloting.Emergency"}) == ALWAYS_ALLOWED
+    for name in ALWAYS_ALLOWED:
+        command = xml_index.get(name)
+        assert command.tier is Tier.MOTION  # locked by tier, exempted by name
+
+
+def test_tier_for_is_what_the_index_stamped():
+    for command in xml_index.all_commands():
+        assert tier_for(command) is command.tier