From 3d71abcca1a7b1743ad5827e31a893f73eb6b427 Mon Sep 17 00:00:00 2001
From: Andras Schmelczer <andras@schmelczer.dev>
Date: Tue, 22 Sep 2026 20:16:04 +0100
Subject: [PATCH] Limit the event response size

---
 sync-server/src/app_state/database/queries.rs | 28 ++++++++++++++++---
 sync-server/src/consts.rs                     |  3 ++
 sync-server/src/server/endpoints/events.rs    |  8 +++++-
 3 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/sync-server/src/app_state/database/queries.rs b/sync-server/src/app_state/database/queries.rs
index 66cda538..10b65d93 100644
--- a/sync-server/src/app_state/database/queries.rs
+++ b/sync-server/src/app_state/database/queries.rs
@@ -7,6 +7,8 @@ use super::{
 };
 use anyhow::{Context as _, Result, ensure};
 
+use crate::consts::MAX_EVENTS_PAGE_BYTES;
+
 impl Database {
     pub async fn get_missing_document(
         tx: &mut Transaction<'_>,
@@ -172,7 +174,12 @@ impl Database {
         })
     }
 
-    pub async fn events_after(&self, vault: &VaultId, after: VaultUpdateId) -> Result<EventBatch> {
+    pub async fn events_after(
+        &self,
+        vault: &VaultId,
+        after: VaultUpdateId,
+        page_size: usize,
+    ) -> Result<EventBatch> {
         let mut tx = self.create_readonly_transaction(vault).await?;
         let head_event_id = Self::latest_event_id(&mut tx).await?;
 
@@ -182,23 +189,36 @@ impl Database {
         );
 
         let rows: Vec<(VaultUpdateId, String)> = sqlx::query_as(
-            "SELECT event_id, request_id FROM events WHERE event_id > ? ORDER BY event_id",
+            "SELECT event_id, request_id FROM events WHERE event_id > ? ORDER BY event_id LIMIT ?",
         )
         .bind(after)
+        .bind(i64::try_from(page_size)?)
         .fetch_all(&mut *tx)
         .await?;
 
         let mut events = Vec::with_capacity(rows.len());
+        let mut bytes = 0;
+        let mut end_event_id = after;
         for (event_id, request_id) in rows {
-            events.push(EventRecord {
+            let event = EventRecord {
                 event_id,
                 request_id: request_id.parse()?,
                 event: Self::event_by_id(&mut tx, event_id).await?,
-            });
+            };
+            let size = serde_json::to_vec(&event)?.len();
+            // One manifest is atomic and may exceed this budget. Always allow
+            // one event so even such a page advances; never accumulate history.
+            if !events.is_empty() && bytes + size > MAX_EVENTS_PAGE_BYTES {
+                break;
+            }
+            bytes += size;
+            end_event_id = event_id;
+            events.push(event);
         }
 
         Ok(EventBatch {
             head_event_id,
+            end_event_id: Some(end_event_id),
             events,
         })
     }
diff --git a/sync-server/src/consts.rs b/sync-server/src/consts.rs
index 71047092..dc5f08b9 100644
--- a/sync-server/src/consts.rs
+++ b/sync-server/src/consts.rs
@@ -21,4 +21,7 @@ pub const WEBSOCKET_SEND_TIMEOUT: Duration = Duration::from_secs(10);
 
 pub const DEFAULT_MERGEABLE_FILE_EXTENSIONS: &[&str] = &["md", "txt"];
 
+pub const DEFAULT_EVENTS_PAGE_SIZE: usize = 64;
+pub const MAX_EVENTS_PAGE_BYTES: usize = 1024 * 1024;
+
 pub const SUPPORTED_API_VERSION: u32 = 4;
diff --git a/sync-server/src/server/endpoints/events.rs b/sync-server/src/server/endpoints/events.rs
index 2505afba..3c2ffd30 100644
--- a/sync-server/src/server/endpoints/events.rs
+++ b/sync-server/src/server/endpoints/events.rs
@@ -8,12 +8,14 @@ use serde::Deserialize;
 use super::VaultPath;
 use crate::{
     app_state::{AppState, database::models::EventBatch},
+    consts::DEFAULT_EVENTS_PAGE_SIZE,
     errors::{SyncServerError, client_error, server_error},
 };
 
 #[derive(Deserialize)]
 pub struct EventsQuery {
     pub after: i64,
+    pub page_size: Option<usize>,
 }
 
 #[axum::debug_handler]
@@ -33,7 +35,11 @@ pub async fn events(
 
     state
         .database
-        .events_after(&vault_id, query.after)
+        .events_after(
+            &vault_id,
+            query.after,
+            query.page_size.unwrap_or(DEFAULT_EVENTS_PAGE_SIZE),
+        )
         .await
         .map(Json)
         .map_err(server_error)