Consider disabling WebSocket message splitting when permessage-deflate is off #7724
Description
WebSocket message splitting adds significant latency for large files on proxied connections
When serving code-server behind a proxy (which is the common production deployment), the 256KB WebSocket message splitting introduced in microsoft/vscode#174278 multiplies per-message RTT overhead significantly for large file operations like image previews.
Background
VS Code splits large IPC messages into 256KB chunks (MaxWebSocketMessageLength = 256 * 1024 in ipc.net.ts) to avoid blocking the Node.js event loop during zlib compression. Each chunk becomes a separate WebSocket message.
The latency problem in proxied deployments
In a proxied deployment (e.g. a gateway in front of a devbox), each WebSocket message incurs a full round-trip. With 100ms RTT between the proxy and the devbox:
- A 10MB file generates ~40 chunks (10MB ÷ 256KB)
- Each chunk = one WebSocket message = one round-trip
- Total overhead: ~40 × 100ms = ~4 seconds of pure latency
We tested image preview times (time from opening a file in the explorer to the image fully rendering) across different file sizes at 100ms simulated RTT:
| File size | Splitting ON | Splitting OFF | Improvement |
|---|---|---|---|
| 145 KB | 2,212ms | 2,251ms | ~0% |
| 1 MB | 1,988ms | 1,707ms | 14% |
| 1.5 MB | 2,093ms | 1,412ms | 33% |
| 5.6 MB | 4,255ms | 2,193ms | 48% |
| 10.3 MB | 7,262ms | 2,888ms | 60% |
Is disabling splitting safe? (Does zlib actually block?)
A few basic tests didn't seem to indicate this issue in our case, but more investigation may be needed
Question
Would you consider making enableMessageSplitting configurable via a CLI flag, or defaulting it to false for single-user deployments?
Happy to submit a PR if there's agreement on the right approach.