#server.compress

• Type:

type Compress =
  | boolean
  | {
      filter?: (req: IncomingMessage, res: ServerResponse) => boolean;
      level?: number;
    };

• Default: true

Configure whether to enable gzip compression for static assets served by the dev server or preview server.

#Disable compression

To disable the gzip compression, set compress to false:

export default {
  server: {
    compress: false,
  },
};

#Options

#filter

• Type: (req: IncomingMessage, res: ServerResponse) => boolean
• Default: undefined
• Version: >= v1.4.4

A function that determines whether a response should be compressed.

Returns true to compress the response, false to skip compression.

export default {
  server: {
    compress: {
      filter: (req) => {
        if (req.url?.includes('/foo')) {
          return false;
        }
        return true;
      },
    },
  },
};

#level

• Type: number
• Default:
  • Dev server: 1 (zlib.constants.Z_BEST_SPEED)
  • Preview server: 6 (zlib.constants.Z_DEFAULT_COMPRESSION)
• Version: >= v1.4.4

Used to set the level of zlib compression applied to responses. A higher level will result in better compression, but will take longer to complete; a lower level will result in less compression, but will be much faster. This value is an integer in the range of 0 (no compression) to 9 (maximum compression).

Rsbuild dev server uses zlib.constants.Z_BEST_SPEED as the default compression level, which provides the best compression performance. The preview server sets level to zlib.constants.Z_DEFAULT_COMPRESSION by default.

export default {
  server: {
    compress: {
      level: 6,
    },
  },
};

#Streaming responses

Gzip compression may buffer data, delaying delivery of streamed HTML. To send a chunk without waiting for the response to end, call res.flush?.() after res.write().

res.setHeader('Content-Type', 'text/html');
res.write('<!doctype html><html><body><p>Loading...</p>');
res.flush?.();

// Continue writing as data becomes available, then call res.end().

res.flush() flushes the gzip buffer without ending the response. It is provided by the compression middleware, so use optional chaining (?.) to handle cases where the method is unavailable, such as when compression is disabled.

When using server.setup, register your streaming handler with server.middlewares.use() inside the returned callback so the compression middleware runs first. See Middleware execution order.