1 files changed, 60 insertions, 0 deletions
diff --git a/src/get-request-cache-key.js b/src/get-request-cache-key.js
new file mode 100644
index 0000000..9c98cb5
--- /dev/null
+++ b/src/get-request-cache-key.js
@@ -0,0 +1,60 @@
+import { normalizeUrl } from './normalize-url'
+
+export async function getRequestCacheKey(request) {
+  try {
+    // Respect "pragma: no-cache" header
+    const pragma = request.headers.get('pragma')
+    if (pragma === 'no-cache') {
+      return null
+    }
+
+    // Only cache readonly requests
+    if (request.method !== 'GET' && request.method !== 'HEAD') {
+      return null
+    }
+
+    // Respect "cache-control" header directives
+    const cacheControl = request.headers.get('cache-control')
+    if (cacheControl) {
+      const directives = new Set(cacheControl.split(',').map((s) => s.trim()))
+      if (directives.has('no-store') || directives.has('no-cache')) {
+        return null
+      }
+    }
+
+    const url = request.url
+    const normalizedUrl = normalizeUrl(url)
+
+    if (url !== normalizedUrl) {
+      return normalizeRequestHeaders(
+        new Request(normalizedUrl, { method: request.method })
+      )
+    }
+
+    return normalizeRequestHeaders(new Request(request))
+  } catch (err) {
+    console.error('error computing cache key', request.method, request.url, err)
+    return null
+  }
+}
+
+const requestHeaderWhitelist = new Set([
+  'cache-control',
+  'accept',
+  'accept-encoding',
+  'accept-language',
+  'user-agent'
+])
+
+function normalizeRequestHeaders(request) {
+  const headers = Object.fromEntries(request.headers.entries())
+  const keys = Object.keys(headers)
+
+  for (const key of keys) {
+    if (!requestHeaderWhitelist.has(key)) {
+      request.headers.delete(key)
+    }
+  }
+
+  return request
+}