v2.4.2

Tako 2.4.2 fixes two WebSocket problems that running Tako in HttpArena brought to light: each connection's read buffer was zero-filled before every socket read, and an upgraded connection stopped counting toward max_connections and the per-thread balancer as soon as the upgrade completed.

No code changes are needed. All eight workspace crates are versioned together at 2.4.2 and require Rust 1.95 or newer.

Performance

• TakoWs reads into a 4 KiB buffer by default instead of tungstenite's 128 KiB. tungstenite zero-fills the spare capacity of its read buffer before every socket read, so each echoed message paid for up to two 128 KiB memsets, and each connection held about 140 KiB. With thousands of connections those memsets no longer fit in cache, and throughput stalled on memory bandwidth. TakoWs::read_buffer_size raises the buffer for large messages. GraphQLSubscription uses the same 4 KiB buffer.

Echoes per second, the median of three 5-second runs in a Docker Linux VM (arm64) on an Apple M4 Max, with serve_per_thread on 4 vCPUs and the load generator on 4 more, each connection echoing a 5-byte text message one at a time:

Workload	2.4.1	2.4.2
Echo, 512 connections	330,572	459,906
Echo, 4,096 connections	312,075	447,724
Echo, 16,384 connections	254,425	394,795
Echo, a new connection every 10 messages, 512 connections	166,483	286,834

At 16,384 connections the server's resident memory drops from 2.2 GiB to 187 MiB.

Fixed

• An upgraded connection, such as a WebSocket, keeps its max_connections permit and its serve_per_thread balancer slot until its socket closes. Both used to be released when the HTTP/1 connection handed its socket to the upgrade, so open WebSockets did not count against max_connections, and the per-thread balancer placed new connections as if they were not there. This covers the TCP, TLS, Unix socket, vsock, and PROXY protocol listeners and the per-thread server; the Compio listeners are unchanged. If you set max_connections, size it for your open WebSockets too.

Full diff: v2.4.1...v2.4.2