test(crypto): Factor out test helper for encrypting to-device content

I'm going to need to suppress `sender_device_keys` for more tests, so pull out
a test helper to help with this.

crates/matrix-sdk-crypto/src/machine/test_helpers.rs

@@ -33,23 +33,23 @@ use ruma::{
     to_device::DeviceIdOrAllDevices,
     user_id, DeviceId, OwnedOneTimeKeyId, TransactionId, UserId,
 };
+use serde::Serialize;
 use serde_json::{json, Value};
 use tokio::sync::Mutex;
 
 use crate::{
     machine::tests,
     olm::PrivateCrossSigningIdentity,
-    session_manager::CollectStrategy,
     store::{types::Changes, CryptoStoreWrapper, MemoryStore},
     types::{
-        events::ToDeviceEvent,
+        events::{room::encrypted::ToDeviceEncryptedEventContent, ToDeviceEvent},
         requests::{AnyOutgoingRequest, ToDeviceRequest},
         DeviceKeys,
     },
     utilities::json_convert,
     verification::VerificationMachine,
-    Account, CrossSigningBootstrapRequests, DecryptionSettings, Device, DeviceData,
-    EncryptionSyncChanges, OlmMachine, OtherUserIdentityData, TrustRequirement,
+    Account, CollectStrategy, CrossSigningBootstrapRequests, DecryptionSettings, Device,
+    DeviceData, EncryptionSyncChanges, OlmMachine, OtherUserIdentityData, TrustRequirement,
 };
 
 /// These keys need to be periodically uploaded to the server.
@@ -227,6 +227,58 @@ pub async fn send_and_receive_encrypted_to_device_test_helper(
     decrypted[0].clone()
 }
 
+/// Encrypt the given event content into the content of an
+/// olm-encrypted to-device event, suppressing the `sender_device_keys` field in
+/// the encrypted content.
+///
+/// This is much the same as calling [`Device::encrypt`] on the recipient
+/// device, other than the suppression of `sender_device_keys`.
+///
+/// # Arguments
+///
+/// * `sender` - The OlmMachine to use to encrypt the event.
+/// * `recipient` - The recipient of the encrypted event.
+/// * `event_type` - The type of the event to encrypt.
+/// * `content` - The content of the event to encrypt.
+pub async fn build_encrypted_to_device_content_without_sender_data(
+    sender: &OlmMachine,
+    recipient_device: &DeviceKeys,
+    event_type: &str,
+    content: &impl Serialize,
+) -> ToDeviceEncryptedEventContent {
+    let sender_store = &sender.inner.store;
+
+    let sender_key = recipient_device.curve25519_key().unwrap();
+    let sessions = sender_store
+        .get_sessions(&sender_key.to_base64())
+        .await
+        .expect("Could not get most recent session")
+        .expect("No olm session found");
+    let mut olm_session = sessions.lock().await.first().unwrap().clone();
+
+    let plaintext = serde_json::to_string(&json!({
+        "sender": sender.user_id(),
+        "sender_device": sender.device_id(),
+        "keys": { "ed25519": sender.identity_keys().ed25519.to_base64() },
+        "recipient": recipient_device.user_id,
+        "recipient_keys": { "ed25519": recipient_device.ed25519_key().unwrap().to_base64() },
+        "type": event_type,
+        "content": content,
+    }))
+    .unwrap();
+
+    let ciphertext = olm_session.encrypt_helper(&plaintext).await;
+    let content =
+        olm_session.build_encrypted_event(ciphertext, None).await.expect("could not encrypt");
+
+    sender_store
+        .save_changes(Changes { sessions: vec![olm_session], ..Default::default() })
+        .await
+        .expect("Could not save session");
+
+    content
+}
+
 /// Create a session for the two supplied Olm machines to communicate.
 pub async fn build_session_for_pair(
     alice: OlmMachine,

crates/matrix-sdk-crypto/src/machine/tests/send_encrypted_to_device.rs

@@ -28,8 +28,9 @@ use serde_json::{json, value::to_raw_value, Value};
 use crate::{
     machine::{
         test_helpers::{
-            build_session_for_pair, get_machine_pair, get_machine_pair_with_session,
-            get_prepared_machine_test_helper, send_and_receive_encrypted_to_device_test_helper,
+            build_encrypted_to_device_content_without_sender_data, build_session_for_pair,
+            get_machine_pair, get_machine_pair_with_session, get_prepared_machine_test_helper,
+            send_and_receive_encrypted_to_device_test_helper,
         },
         tests::{self, decryption_verification_state::mark_alice_identity_as_verified_test_helper},
     },
@@ -45,7 +46,7 @@ use crate::{
     utilities::json_convert,
     verification::tests::bob_id,
     CrossSigningBootstrapRequests, DecryptionSettings, DeviceData, EncryptionSettings,
-    EncryptionSyncChanges, LocalTrust, OlmError, OlmMachine, Session, TrustRequirement,
+    EncryptionSyncChanges, LocalTrust, OlmError, OlmMachine, TrustRequirement,
 };
 
 #[async_test]
@@ -635,33 +636,22 @@ async fn create_and_share_session_without_sender_data(
     // the behaviour of the real implementation. See
     // `GroupSessionManager::share_room_key` for inspiration on how to do that.
 
-    let olm_sessions = alice
-        .store()
-        .get_sessions(&bob.identity_keys().curve25519.to_base64())
+    let bob_device = alice
+        .get_device(bob.user_id(), bob.device_id(), None)
         .await
         .unwrap()
-        .unwrap();
-    let mut olm_session: Session = olm_sessions.lock().await[0].clone();
-
+        .expect("Attempt to send message to unknown device");
     let room_key_content = outbound_session.as_content().await;
-    let plaintext = serde_json::to_string(&json!({
-        "sender": alice.user_id(),
-        "sender_device": alice.device_id(),
-        "keys": { "ed25519": alice.identity_keys().ed25519.to_base64() },
-        // We deliberately do *not* include:
-        // "org.matrix.msc4147.device_keys": alice_device_keys,
-        "recipient": bob.user_id(),
-        "recipient_keys": { "ed25519": bob.identity_keys().ed25519.to_base64() },
-        "type": room_key_content.event_type(),
-        "content": room_key_content,
-    }))
-    .unwrap();
 
-    let ciphertext = olm_session.encrypt_helper(&plaintext).await;
-    ToDeviceEvent::new(
-        alice.user_id().to_owned(),
-        olm_session.build_encrypted_event(ciphertext, None).await.unwrap(),
+    let content = build_encrypted_to_device_content_without_sender_data(
+        alice,
+        &bob_device.device_keys,
+        room_key_content.event_type(),
+        &room_key_content,
     )
+    .await;
+
+    ToDeviceEvent::new(alice.user_id().to_owned(), content)
 }
 
 /// Simulate uploading keys for alice that mean bob thinks alice's device