WebSocket Per-Message Deflate Extension
WS-RS supports the permessage-deflate extension as defined in RFC 7692, allowing compression of WebSocket messages to reduce bandwidth usage.
What is Per-Message Deflate?
Per-message deflate is a WebSocket extension that compresses individual messages using the DEFLATE algorithm. This can significantly reduce bandwidth usage, especially for text-heavy applications.
Benefits
- Reduced Bandwidth - Compress messages by 50-90% for text data
- Lower Latency - Smaller messages travel faster over the network
- Cost Savings - Reduce data transfer costs
- Automatic Negotiation - Enabled during WebSocket handshake
Enabling Deflate Compression
Enable compression in your WS-RS server:
use ws_rs::{WebSocketServer, Config};
#[tokio::main]
async fn main() -> Result<(), Box> {
let config = Config {
compression: true,
compression_level: 6, // 1-9, default is 6
max_message_size: 10 * 1024 * 1024, // 10MB
..Default::default()
};
let server = WebSocketServer::with_config("127.0.0.1:8080", config);
server.on_message(|client_id, message| {
println!("Received compressed message from {}", client_id);
// Message is automatically decompressed
});
server.start().await?;
Ok(())
} Client-Side Support
Modern browsers automatically support deflate compression:
// Browser automatically negotiates compression
const ws = new WebSocket('ws://localhost:8080');
ws.onopen = () => {
// Messages are automatically compressed if server supports it
ws.send('This message will be compressed');
};Compression Parameters
| Parameter | Description | Default |
|---|---|---|
server_no_context_takeover |
Server resets compression context after each message | false |
client_no_context_takeover |
Client resets compression context after each message | false |
server_max_window_bits |
Server LZ77 sliding window size (8-15) | 15 |
client_max_window_bits |
Client LZ77 sliding window size (8-15) | 15 |
Performance Considerations
While compression reduces bandwidth, it adds CPU overhead:
- Best for Text - Text data compresses well (50-90% reduction)
- Not for Binary - Pre-compressed data (images, video) won't benefit
- CPU vs Bandwidth - Trade CPU time for network bandwidth
- Small Messages - Messages under 1KB may not benefit
Testing Compression
Verify compression is working:
// Check WebSocket extensions in browser console
const ws = new WebSocket('ws://localhost:8080');
ws.onopen = () => {
console.log('Extensions:', ws.extensions);
// Should show: "permessage-deflate"
};