Custom error for TryFrom<EncryptionInfo>

Currently, we use `anyhow::Error` to reflect problems with the encryption
algorithm info. Let's drop the dependency on `anyhow` and tighten up the error
handling by defining a custom error type.

Author: richvdh

Cargo.lock

@@ -71,6 +71,7 @@ matrix-sdk-qrcode = { git = "https://github.com/matrix-org/matrix-rust-sdk", rev
 serde = "1.0.91"
 serde_json = "1.0.91"
 serde-wasm-bindgen = "0.6.5"
+thiserror = "2.0.12"
 tracing = { version = "0.1.36", default-features = false, features = ["std"] }
 tracing-subscriber = { version = "0.3.14", default-features = false, features = ["registry", "std", "ansi"] }
 url = "2.5.0"

Cargo.toml

@@ -38,7 +38,7 @@ use crate::{
     future::{future_to_promise, future_to_promise_with_custom_error},
     identifiers, identities, olm, requests,
     requests::{outgoing_request_to_js_value, CrossSigningBootstrapRequests, ToDeviceRequest},
-    responses::{self, response_from_string},
+    responses::{self, response_from_string, UnsupportedAlgorithmError},
     store,
     store::{RoomKeyInfo, RoomKeyWithheldInfo, StoreHandle},
     sync_events,
@@ -511,13 +511,15 @@ impl OlmMachine {
                 .map_err(MegolmDecryptionError::from)?
                 .into();
 
-            responses::DecryptedRoomEvent::try_from(room_event).map_err(|e: anyhow::Error| {
-                // This happens if we somehow encounter a room event whose encryption info we
-                // don't understand (e.g., it is encrypted with Olm rather than
-                // Megolm). That seems pretty unlikely. If it happens, let's
-                // just treat it as a generic UTD.
-                MegolmDecryptionError::unable_to_decrypt(format!("{e:#}"))
-            })
+            responses::DecryptedRoomEvent::try_from(room_event).map_err(
+                |e: UnsupportedAlgorithmError| {
+                    // This happens if we somehow encounter a room event whose encryption info we
+                    // don't understand (e.g., it is encrypted with Olm rather than
+                    // Megolm). That seems pretty unlikely. If it happens, let's
+                    // just treat it as a generic UTD.
+                    MegolmDecryptionError::unable_to_decrypt(format!("{e:#}"))
+                },
+            )
         }))
     }
 

src/machine.rs

@@ -2,7 +2,6 @@
 
 use std::sync::Arc;
 
-use anyhow::anyhow;
 use js_sys::{Array, JsString};
 pub(crate) use matrix_sdk_common::ruma::api::client::{
     backup::add_backup_keys::v3::Response as KeysBackupResponse,
@@ -19,6 +18,7 @@ use matrix_sdk_common::{
     ruma::{self, api::IncomingResponse as RumaIncomingResponse},
 };
 use matrix_sdk_crypto::types::requests::AnyIncomingResponse;
+use thiserror::Error;
 use wasm_bindgen::prelude::*;
 
 use crate::{encryption, identifiers, requests::RequestType};
@@ -216,7 +216,7 @@ impl DecryptedRoomEvent {
 }
 
 impl TryFrom<matrix_sdk_common::deserialized_responses::TimelineEvent> for DecryptedRoomEvent {
-    type Error = anyhow::Error;
+    type Error = UnsupportedAlgorithmError;
 
     fn try_from(
         value: matrix_sdk_common::deserialized_responses::TimelineEvent,
@@ -288,7 +288,7 @@ impl EncryptionInfo {
 }
 
 impl TryFrom<Arc<matrix_sdk_common::deserialized_responses::EncryptionInfo>> for EncryptionInfo {
-    type Error = anyhow::Error;
+    type Error = UnsupportedAlgorithmError;
 
     fn try_from(
         value: Arc<matrix_sdk_common::deserialized_responses::EncryptionInfo>,
@@ -306,8 +306,8 @@ impl TryFrom<Arc<matrix_sdk_common::deserialized_responses::EncryptionInfo>> for
                     verification_state: value.verification_state.clone(),
                 })
             }
-            AlgorithmInfo::OlmV1Curve25519AesSha2 { .. } => Err(anyhow!(
-                "AlgorithmInfo::OlmV1Curve25519AesSha2 is not applicable for room event EncryptionInfo",
+            AlgorithmInfo::OlmV1Curve25519AesSha2 { .. } => Err(UnsupportedAlgorithmError(
+                "AlgorithmInfo::OlmV1Curve25519AesSha2 is not applicable for room event EncryptionInfo".to_owned()
             )),
         }
     }
@@ -344,14 +344,15 @@ pub struct ToDeviceEncryptionInfo {
 }
 
 impl TryFrom<matrix_sdk_common::deserialized_responses::EncryptionInfo> for ToDeviceEncryptionInfo {
-    type Error = anyhow::Error;
+    type Error = UnsupportedAlgorithmError;
 
     fn try_from(
         value: matrix_sdk_common::deserialized_responses::EncryptionInfo,
     ) -> Result<Self, Self::Error> {
         match &value.algorithm_info {
-            AlgorithmInfo::MegolmV1AesSha2 { .. } => Err(anyhow!(
-                "AlgorithmInfo::MegolmV1AesSha2 is not applicable for ToDeviceEncryptionInfo",
+            AlgorithmInfo::MegolmV1AesSha2 { .. } => Err(UnsupportedAlgorithmError(
+                "AlgorithmInfo::MegolmV1AesSha2 is not applicable for ToDeviceEncryptionInfo"
+                    .to_owned(),
             )),
             AlgorithmInfo::OlmV1Curve25519AesSha2 { curve25519_public_key_base64 } => Ok(Self {
                 sender_curve25519_key_base64: curve25519_public_key_base64.clone(),
@@ -375,3 +376,11 @@ impl ToDeviceEncryptionInfo {
         )
     }
 }
+
+/// Error type returned when converting
+/// [`matrix_sdk_common::deserialized_responses::EncryptionInfo`] to one of our
+/// own types: the `algorithm_info` on the `EncryptionInfo` was of an unexpected
+/// type.
+#[derive(Error, Debug)]
+#[error("{0}")]
+pub struct UnsupportedAlgorithmError(String);