ETag (API Reference)

setConfig({ etag })

app.setConfig({ etag: true });
app.setConfig({ etag: { weak: true, exclude: ['/stream/*'] } });

Configures ETag generation globally. When activated, responses include an ETag header representing the body contents, and the server automatically processes If-None-Match headers to return 304 Not Modified.

Parameter	Type	Description
etag	boolean | EtagOptions	true = strong ETags. Object = full options. false = disable.

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app.useEtag(options?)

app.useEtag(options?)

Alternative to setConfig, enables ETags and returns the app instance for chaining.

Parameter	Type	Default	Description
options.weak	boolean	false	If true, generates weak ETags (W/"...")
options.exclude	string[]	[]	Paths that should not receive ETags

Returns

KaelumApp — the app instance for chaining.

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EtagOptions

interface EtagOptions {
  weak?: boolean;
  exclude?: string[];
}

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Behavior Details

• Dependencies: Uses Express’s native ETag engine and Node’s native crypto.createHash('sha1'). No external packages required.
• Weak vs Strong: Strong ETags indicate byte-for-byte equivalence. Weak ETags (prefixed with W/) indicate semantic equivalence.
• Excluded Paths: Paths matching strings or wildcards (/*) in the exclude array will have their ETag header stripped before the response is finalized. Useful for streams or Server-Sent Events.

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Examples

// Strong ETags (default)
app.setConfig({ etag: true });

// Weak ETags
app.useEtag({ weak: true });

// Exclude specific paths
app.setConfig({
  etag: {
    exclude: [
      '/sse',         // Exact match
      '/webhooks/*',  // Wildcard match
    ],
  },
});