base_station: fix error if sensor not found

Creating a bluer::Device doesn't actually check whether the device
exists. Add an additional check whether we can read the device name, and
translate the relevant BlueZ errors to a more descriptive error.

Author: lopsided98

base_station/src/sensor.rs

@@ -1,19 +1,18 @@
-use std::borrow::Cow;
 use std::io;
 use std::io::Cursor;
 
 use bluer::Address;
 use byteorder::{LittleEndian, ReadBytesExt};
 use futures::StreamExt;
 use thiserror::Error;
-use uuid::{uuid, Uuid};
+use uuid::{Uuid, uuid};
 
 #[derive(Debug, Error)]
 pub enum Error {
     #[error("sensor with address {0} not found")]
     SensorNotFound(bluer::Address),
-    #[error("sensor cannot be used: {0}")]
-    SensorInvalid(Cow<'static, str>),
+    #[error("sensor is not paired")]
+    SensorNotPaired,
     #[error("GATT attribute '{0}' not found")]
     GattAttributeNotFound(Uuid),
     #[error("sensor is not connected")]
@@ -45,9 +44,6 @@ pub struct Sensor {
 }
 
 impl Sensor {
-    // Characteristic Presentation Format
-    const CPF_UUID: &'static str = "00002904-0000-1000-8000-00805f9b34fb";
-
     // Battery Service
     const BAS_UUID: Uuid = uuid!("0000180f-0000-1000-8000-00805f9b34fb");
     const BAS_BATTERY_LEVEL_UUID: Uuid = uuid!("00002a19-0000-1000-8000-00805f9b34fb");
@@ -70,7 +66,7 @@ impl Sensor {
 
     async fn new(device: bluer::Device) -> Result<Self, Error> {
         if !device.is_paired().await? {
-            return Err(Error::SensorInvalid("not paired".into()));
+            return Err(Error::SensorNotPaired);
         }
 
         Ok(Sensor { device, gatt: None })
@@ -80,12 +76,18 @@ impl Sensor {
         adapter: &bluer::Adapter,
         address: bluer::Address,
     ) -> Result<Sensor, Error> {
-        Self::new(
-            adapter
-                .device(address)
-                .map_err(|_| Error::SensorNotFound(address))?,
-        )
-        .await
+        // Creating the device does not actually check the DBus object exists
+        let device = adapter.device(address)?;
+        // Therefore, try to get the name to confirm device exists
+        device.name().await.map_err(|e| match e {
+            bluer::Error {
+                kind: bluer::ErrorKind::NotFound | bluer::ErrorKind::DoesNotExist,
+                ..
+            } => Error::SensorNotFound(address),
+            _ => e.into(),
+        })?;
+
+        Self::new(device).await
     }
 
     async fn find_service(
@@ -189,6 +191,7 @@ impl Sensor {
                 monitor_type: bluer::monitor::Type::OrPatterns,
                 patterns: Some(vec![bluer::monitor::Pattern {
                     start_position: 0,
+                    // Service Data
                     data_type: 0x21,
                     content: vec![
                         0xa1, 0xf8, 0x20, 0x0f, 0xa2, 0xc0, 0x4e, 0x72, 0x8e, 0x88, 0x61, 0x96,