feat: handleCacheHeaders utility

src/utils/cache.ts

@@ -0,0 +1,50 @@
+import type { CompatibilityEvent } from '../event'
+
+export interface CacheConditions {
+  modifiedTime?: Date
+  maxAge?: number
+  etag?: string
+  cacheControls?: string[]
+}
+
+/**
+ * Check request caching headers (`If-Modified-Since`) and add caching headers (Last-Modified, Cache-Control)
+ * Note: `public` cache control will be added by default
+ * @returns `true` when cache headers are matching. When `true` is returned, no reponse should be sent anymore
+ */
+export function handleCacheHeaders (event: CompatibilityEvent, opts: CacheConditions): boolean {
+  const cacheControls = ['public'].concat(opts.cacheControls || [])
+  let cacheMatched = false
+
+  if (opts.maxAge !== undefined) {
+    opts.cacheControls?.push(`max-age=${+opts.maxAge}`, `s-maxage=${+opts.maxAge}`)
+  }
+
+  if (opts.modifiedTime) {
+    const ifModifiedSince = event.req.headers['if-modified-since']
+    event.res.setHeader('Last-Modified', +opts.modifiedTime + '')
+    if (ifModifiedSince) {
+      if (new Date(ifModifiedSince) >= opts.modifiedTime) {
+        cacheMatched = true
+      }
+    }
+  }
+
+  if (opts.etag) {
+    event.res.setHeader('Etag', opts.etag)
+    const ifNonMatch = event.req.headers['if-none-match']
+    if (ifNonMatch === opts.etag) {
+      cacheMatched = true
+    }
+  }
+
+  event.res.setHeader('Cache-Control', cacheControls.join(', '))
+
+  if (cacheMatched) {
+    event.res.statusCode = 304
+    event.res.end('')
+    return true
+  }
+
+  return false
+}

src/utils/index.ts

@@ -1,4 +1,5 @@
 export * from './body'
+export * from './cache'
 export * from './consts'
 export * from './cookie'
 export * from './request'