crypto: indicate when a device was updated

update `ReadOnlyDevice::update_device` to return a bool indicating whether
anything is changing.

crates/matrix-sdk-crypto/src/identities/device.rs

@@ -848,7 +848,12 @@ impl ReadOnlyDevice {
     }
 
     /// Update a device with a new device keys struct.
-    pub(crate) fn update_device(&mut self, device_keys: &DeviceKeys) -> Result<(), SignatureError> {
+    ///
+    /// Returns `true` if any changes were made to the data.
+    pub(crate) fn update_device(
+        &mut self,
+        device_keys: &DeviceKeys,
+    ) -> Result<bool, SignatureError> {
         self.verify_device_keys(device_keys)?;
 
         if self.user_id() != device_keys.user_id || self.device_id() != device_keys.device_id {
@@ -858,10 +863,13 @@ impl ReadOnlyDevice {
                 self.ed25519_key().map(Box::new),
                 device_keys.ed25519_key().map(Box::new),
             ))
-        } else {
+        } else if self.inner.as_ref() != device_keys {
             self.inner = device_keys.clone().into();
 
-            Ok(())
+            Ok(true)
+        } else {
+            // no changes needed
+            Ok(false)
         }
     }
 
@@ -1066,9 +1074,11 @@ pub(crate) mod tests {
 
         let mut device_keys = device_keys();
         device_keys.unsigned.device_display_name = Some(display_name.clone());
-        device.update_device(&device_keys).unwrap();
-
+        assert!(device.update_device(&device_keys).unwrap());
         assert_eq!(&display_name, device.display_name().as_ref().unwrap());
+
+        // A second call to `update_device` with the same data should return `false`.
+        assert!(!device.update_device(&device_keys).unwrap());
     }
 
     #[test]

crates/matrix-sdk-crypto/src/types/device_keys.rs

@@ -39,7 +39,7 @@ use super::{EventEncryptionAlgorithm, Signatures};
 /// identity keys.
 ///
 /// [device_keys_spec]: https://spec.matrix.org/v1.10/client-server-api/#_matrixclientv3keysupload_devicekeys
-#[derive(Clone, Debug, Deserialize, Serialize)]
+#[derive(Clone, Debug, Deserialize, Serialize, PartialEq)]
 #[serde(try_from = "DeviceKeyHelper", into = "DeviceKeyHelper")]
 pub struct DeviceKeys {
     /// The ID of the user the device belongs to.
@@ -130,7 +130,7 @@ impl DeviceKeys {
 }
 
 /// Additional data added to device key information by intermediate servers.
-#[derive(Clone, Debug, Default, Deserialize, Serialize)]
+#[derive(Clone, Debug, Default, Deserialize, Serialize, PartialEq)]
 pub struct UnsignedDeviceInfo {
     /// The display name which the user set on the device.
     #[serde(skip_serializing_if = "Option::is_none")]