implement filter.limit in /context

This seems to be completely redundant with the 'limit' body parameter,
with the only difference being:

> The filter may be applied before or/and after the limit parameter -
filter> whichever the homeserver prefers.

This sentence seems to apply to the 'limit' body parameter, but not to
the 'limit' field on the filter. This was probably unintentional on the
part of the spec authors, but I've switched to using same 'load_limit'
pattern we're using elsewhere anyway.

src/api/client_server/context.rs

@@ -5,12 +5,14 @@ use ruma::{
         context::get_context, error::ErrorKind, filter::LazyLoadOptions,
     },
     events::StateEventType,
-    uint,
+    uint, UInt,
 };
 use tracing::error;
 
 use crate::{
-    services, utils::filter::CompiledRoomEventFilter, Ar, Error, Ra, Result,
+    services,
+    utils::filter::{load_limit, CompiledRoomEventFilter},
+    Ar, Error, Ra, Result,
 };
 
 /// # `GET /_matrix/client/r0/rooms/{roomId}/context`
@@ -77,9 +79,13 @@ pub(crate) async fn get_context_route(
         lazy_loaded.insert(base_event.sender.as_str().to_owned());
     }
 
-    // Use limit with maximum 100
-    let half_limit = usize::try_from(body.limit.min(uint!(100)) / uint!(2))
-        .expect("0-50 should fit in usize");
+    let limit: usize = body
+        .limit
+        .min(body.filter.limit.unwrap_or(UInt::MAX))
+        .min(uint!(100))
+        .try_into()
+        .expect("0-100 should fit in usize");
+    let half_limit = limit / 2;
 
     let base_event = base_event.to_room_event();
 
@@ -105,7 +111,7 @@ pub(crate) async fn get_context_route(
         .rooms
         .timeline
         .pdus_until(sender_user, &room_id, base_token)?
-        .take(half_limit)
+        .take(load_limit(half_limit))
         .filter_map(Result::ok)
         .filter(|(_, pdu)| {
             services()
@@ -114,6 +120,7 @@ pub(crate) async fn get_context_route(
                 .user_can_see_event(sender_user, &room_id, &pdu.event_id)
                 .unwrap_or(false)
         })
+        .take(half_limit)
         .collect();
 
     for (_, event) in &events_before {
@@ -139,7 +146,7 @@ pub(crate) async fn get_context_route(
         .rooms
         .timeline
         .pdus_after(sender_user, &room_id, base_token)?
-        .take(half_limit)
+        .take(load_limit(half_limit))
         .filter_map(Result::ok)
         .filter(|(_, pdu)| {
             services()
@@ -148,6 +155,7 @@ pub(crate) async fn get_context_route(
                 .user_can_see_event(sender_user, &room_id, &pdu.event_id)
                 .unwrap_or(false)
         })
+        .take(half_limit)
         .collect();
 
     for (_, event) in &events_after {