crypto: Encrypt room keys for a room key share request in parallel

matrix_sdk_crypto/Cargo.toml

@@ -29,6 +29,8 @@ serde_json = "1.0.61"
 zeroize = { version = "1.2.0", features = ["zeroize_derive"] }
 
 # Misc dependencies
+tokio = { version = "1.1.0", default-features = false, features = ["rt", "rt-multi-thread"] }
+futures = "0.3.12"
 sled = { version = "0.34.6", optional = true }
 thiserror = "1.0.23"
 tracing = "0.1.22"
@@ -44,7 +46,6 @@ byteorder = "1.4.2"
 
 [dev-dependencies]
 tokio = { version = "1.1.0", default-features = false, features = ["rt-multi-thread", "macros"] }
-futures = "0.3.12"
 proptest = "0.10.1"
 serde_json = "1.0.61"
 tempfile = "3.2.0"

matrix_sdk_crypto/src/session_manager/group_sessions.rs

@@ -17,6 +17,10 @@ use std::{
     sync::Arc,
 };
 
+use futures::future::join_all;
+
+use tokio;
+
 use dashmap::DashMap;
 use matrix_sdk_common::{
     api::r0::to_device::DeviceIdOrAllDevices,
@@ -195,28 +199,46 @@ impl GroupSessionManager {
         let mut messages = BTreeMap::new();
         let mut changed_sessions = Vec::new();
 
-        for device in devices {
+        let encrypt = |device: Device, content: Value| async move {
+            let mut message = BTreeMap::new();
+
             let encrypted = device.encrypt(EventType::RoomKey, content.clone()).await;
 
-            let (used_session, encrypted) = match encrypted {
+            let used_session = match encrypted {
-                Ok(c) => c,
+                Ok((session, encrypted)) => {
-                // TODO we'll want to create m.room_key.withheld here.
+                    message
-                Err(OlmError::MissingSession)
-                | Err(OlmError::EventError(EventError::MissingSenderKey)) => {
-                    continue;
-                }
-                Err(e) => return Err(e),
-            };
-
-            changed_sessions.push(used_session);
-
-            messages
                         .entry(device.user_id().clone())
                         .or_insert_with(BTreeMap::new)
                         .insert(
                             DeviceIdOrAllDevices::DeviceId(device.device_id().into()),
                             serde_json::value::to_raw_value(&encrypted)?,
                         );
+                    Some(session)
+                }
+                // TODO we'll want to create m.room_key.withheld here.
+                Err(OlmError::MissingSession)
+                | Err(OlmError::EventError(EventError::MissingSenderKey)) => None,
+                Err(e) => return Err(e),
+            };
+
+            Ok((used_session, message))
+        };
+
+        let tasks: Vec<_> = devices
+            .iter()
+            .map(|d| tokio::spawn(encrypt(d.clone(), content.clone())))
+            .collect();
+
+        let results = join_all(tasks).await;
+
+        for result in results {
+            let (used_session, message) = result.expect("Encryption task paniced")?;
+
+            if let Some(session) = used_session {
+                changed_sessions.push(session);
+            }
+
+            messages.extend(message);
         }
 
         let id = Uuid::new_v4();