livekit-datatrack: stop aborting when a foreign E2EE provider errors

.changeset/liftable_e2ee_provider_errors.md

@@ -0,0 +1,9 @@
+---
+livekit-datatrack: major
+livekit-uniffi: major
+livekit: patch
+livekit-ffi: patch
+livekit-capture: patch
+---
+
+`EncryptionError::Failed` and `DecryptionError::Failed` carry a `reason` string and are no longer `flat_error`, so a foreign `EncryptionProvider` or `DecryptionProvider` returning an error no longer aborts the process with "Can't lift flat errors" -- a failed data track decrypt (no E2EE manager, key mismatch, corrupt frame) now drops the frame and leaves the room connected.

livekit-datatrack/src/e2ee.rs

@@ -33,19 +33,35 @@ pub struct EncryptedPayload {
 /// An error indicating a payload could not be encrypted.
 #[derive(Debug, Error)]
 #[cfg_attr(feature = "uniffi", derive(uniffi::Error))]
-#[cfg_attr(feature = "uniffi", uniffi(flat_error))]
 pub enum EncryptionError {
-    #[error("Encryption failed")]
-    Failed,
+    #[error("Encryption failed: {reason}")]
+    Failed { reason: String },
+}
+
+// Required because foreign code implements `EncryptionProvider::encrypt`: an exception that is
+// NOT an `EncryptionError` surfaces through this catch-all rather than aborting.
+#[cfg(feature = "uniffi")]
+impl From<uniffi::UnexpectedUniFFICallbackError> for EncryptionError {
+    fn from(error: uniffi::UnexpectedUniFFICallbackError) -> Self {
+        Self::Failed { reason: error.reason }
+    }
 }
 
 /// An error indicating a payload could not be decrypted.
 #[derive(Debug, Error)]
 #[cfg_attr(feature = "uniffi", derive(uniffi::Error))]
-#[cfg_attr(feature = "uniffi", uniffi(flat_error))]
 pub enum DecryptionError {
-    #[error("Decryption failed")]
-    Failed,
+    #[error("Decryption failed: {reason}")]
+    Failed { reason: String },
+}
+
+// Required because foreign code implements `DecryptionProvider::decrypt`: an exception that is
+// NOT a `DecryptionError` surfaces through this catch-all rather than aborting.
+#[cfg(feature = "uniffi")]
+impl From<uniffi::UnexpectedUniFFICallbackError> for DecryptionError {
+    fn from(error: uniffi::UnexpectedUniFFICallbackError) -> Self {
+        Self::Failed { reason: error.reason }
+    }
 }
 
 /// Provider for encrypting payloads for E2EE.

livekit/src/room/e2ee/data_track.rs

@@ -37,7 +37,7 @@
         let encrypted = self
             .manager
             .encrypt_data(payload.into(), &self.sender_identity, key_index)
-            .map_err(|_| dt::EncryptionError::Failed)?;
+            .map_err(|e| dt::EncryptionError::Failed { reason: e.to_string() })?;
 
         debug_assert_eq!(
             encrypted.key_index as u32,
@@ -46,8 +46,12 @@
             );
 
         let payload = encrypted.data.into();
-        let iv = encrypted.iv.try_into().map_err(|_| dt::EncryptionError::Failed)?;
-        let key_index = encrypted.key_index.try_into().map_err(|_| dt::EncryptionError::Failed)?;
+        let iv = encrypted.iv.try_into().map_err(|iv: Vec<u8>| dt::EncryptionError::Failed {
+            reason: format!("unexpected IV length: {}", iv.len()),
+        })?;
+        let key_index = encrypted.key_index.try_into().map_err(|e| dt::EncryptionError::Failed {
+            reason: format!("key index out of range: {e}"),
+        })?;
 
         Ok(dt::EncryptedPayload { payload, iv, key_index })
     }
@@ -79,7 +83,9 @@
                 payload.key_index as u32,
                 &sender_identity,
             )
-            .ok_or_else(|| dt::DecryptionError::Failed)?;
+            .ok_or_else(|| dt::DecryptionError::Failed {
+                reason: "the E2EE manager could not decrypt the payload".to_owned(),
+            })?;
         Ok(Bytes::from(decrypted))
     }
 }