Consider disabling WebSocket message splitting when permessage-deflate is off #7724

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:

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.