add util for handling remix headers generally

app/root.tsx

@@ -43,6 +43,7 @@ import { getEnv } from './utils/env.server.ts'
 import { honeypot } from './utils/honeypot.server.ts'
 import { combineHeaders, getDomainUrl, getUserImgSrc } from './utils/misc.tsx'
 import { useNonce } from './utils/nonce-provider.ts'
+import { pipeHeaders } from './utils/remix.server.ts'
 import { type Theme, getTheme } from './utils/theme.server.ts'
 import { makeTimings, time } from './utils/timing.server.ts'
 import { getToast } from './utils/toast.server.ts'
@@ -140,12 +141,7 @@ export async function loader({ request }: LoaderFunctionArgs) {
 	)
 }
 
-export const headers: HeadersFunction = ({ loaderHeaders }) => {
-	const headers = {
-		'Server-Timing': loaderHeaders.get('Server-Timing') ?? '',
-	}
-	return headers
-}
+export const headers: HeadersFunction = pipeHeaders
 
 function Document({
 	children,

app/routes/settings+/profile.connections.tsx

@@ -30,6 +30,7 @@ import { prisma } from '#app/utils/db.server.ts'
 import { makeTimings } from '#app/utils/timing.server.ts'
 import { createToastHeaders } from '#app/utils/toast.server.ts'
 import { type BreadcrumbHandle } from './profile.tsx'
+import { pipeHeaders } from '#app/utils/remix.server.js'
 
 export const handle: BreadcrumbHandle & SEOHandle = {
 	breadcrumb: <Icon name="link-2">Connections</Icon>,
@@ -90,12 +91,7 @@ export async function loader({ request }: LoaderFunctionArgs) {
 	)
 }
 
-export const headers: HeadersFunction = ({ loaderHeaders }) => {
-	const headers = {
-		'Server-Timing': loaderHeaders.get('Server-Timing') ?? '',
-	}
-	return headers
-}
+export const headers: HeadersFunction = pipeHeaders
 
 export async function action({ request }: ActionFunctionArgs) {
 	const userId = await requireUserId(request)
@@ -197,7 +193,7 @@ function Connection({
 									status={
 										deleteFetcher.state !== 'idle'
 											? 'pending'
-											: deleteFetcher.data?.status ?? 'idle'
+											: (deleteFetcher.data?.status ?? 'idle')
 									}
 								>
 									<Icon name="cross-1" />

app/utils/remix.server.test.ts

@@ -0,0 +1,53 @@
+import cacheControl from 'cache-control-parser'
+import { describe, expect, test } from 'vitest'
+import { getConservativeCacheControl } from './remix.server.ts'
+
+describe('getConservativeCacheControl', () => {
+	test('works for basic usecase', () => {
+		const result = getConservativeCacheControl(
+			'max-age=3600',
+			'max-age=1800, s-maxage=600',
+			'private, max-age=86400',
+		)
+
+		expect(result).toEqual(
+			cacheControl.stringify({
+				'max-age': 1800,
+				's-maxage': 600,
+				private: true,
+			}),
+		)
+	})
+	test('retains boolean directive', () => {
+		const result = cacheControl.parse(
+			getConservativeCacheControl('private', 'no-cache,no-store'),
+		)
+
+		expect(result.private).toEqual(true)
+		expect(result['no-cache']).toEqual(true)
+		expect(result['no-store']).toEqual(true)
+	})
+	test('gets smallest number directive', () => {
+		const result = cacheControl.parse(
+			getConservativeCacheControl(
+				'max-age=10, s-maxage=300',
+				'max-age=300, s-maxage=600',
+			),
+		)
+
+		expect(result['max-age']).toEqual(10)
+		expect(result['s-maxage']).toEqual(300)
+	})
+	test('lets unset directives remain unset', () => {
+		const result = cacheControl.parse(
+			getConservativeCacheControl(
+				'max-age=3600',
+				'max-age=1800, s-maxage=600',
+				'private, max-age=86400',
+			),
+		)
+
+		expect(result['must-revalidate']).toBeUndefined()
+		expect(result['stale-while-revalidate']).toBeUndefined()
+	})
+})

app/utils/remix.server.ts

@@ -0,0 +1,106 @@
+import { type HeadersArgs } from '@remix-run/node'
+import { parse, stringify, type CacheControl } from 'cache-control-parser'
+
+export function pipeHeaders({
+	parentHeaders,
+	loaderHeaders,
+	actionHeaders,
+	errorHeaders,
+}: HeadersArgs) {
+	const headers = new Headers()
+
+	// get the one that's actually in use
+	let currentHeaders: Headers
+	if (errorHeaders !== undefined) {
+		currentHeaders = errorHeaders
+	} else if (loaderHeaders.entries().next().done) {
+		currentHeaders = actionHeaders
+	} else {
+		currentHeaders = loaderHeaders
+	}
+
+	// take in useful headers route loader/action
+	// pass this point currentHeaders can be ignored
+	const forwardHeaders = ['Cache-Control', 'Vary', 'Server-Timing']
+	for (const headerName of forwardHeaders) {
+		const header = currentHeaders.get(headerName)
+		if (header) {
+			headers.set(headerName, header)
+		}
+	}
+
+	headers.set(
+		'Cache-Control',
+		getConservativeCacheControl(
+			parentHeaders.get('Cache-Control'),
+			headers.get('Cache-Control'),
+		),
+	)
+
+	// append useful parent headers
+	const inheritHeaders = ['Vary', 'Server-Timing']
+	for (const headerName of inheritHeaders) {
+		const header = parentHeaders.get(headerName)
+		if (header) {
+			headers.append(headerName, header)
+		}
+	}
+
+	// fallback to parent headers if loader don't have
+	const fallbackHeaders = ['Cache-Control', 'Vary']
+	for (const headerName of fallbackHeaders) {
+		if (headers.has(headerName)) {
+			continue
+		}
+		const fallbackHeader = parentHeaders.get(headerName)
+		if (fallbackHeader) {
+			headers.set(headerName, fallbackHeader)
+		}
+	}
+
+	return headers
+}
+
+export function getConservativeCacheControl(
+	...cacheControlHeaders: Array<string | null>
+): string {
+	return stringify(
+		cacheControlHeaders
+			.filter(Boolean)
+			.map((header) => parse(header))
+			.reduce<CacheControl>((acc, current) => {
+				let directive: keyof CacheControl
+				for (directive in current) {
+					const currentValue = current[directive]
+
+					// ts-expect-error because typescript doesn't know it's the same directive.
+					switch (typeof currentValue) {
+						case 'boolean': {
+							if (currentValue) {
+								// @ts-expect-error
+								acc[directive] = true
+							}
+
+							break
+						}
+						case 'number': {
+							const accValue = acc[directive] as number | undefined
+
+							if (accValue === undefined) {
+								// @ts-expect-error
+								acc[directive] = currentValue
+							} else {
+								const result = Math.min(accValue, currentValue)
+								// @ts-expect-error
+								acc[directive] = result
+							}
+
+							break
+						}
+					}
+				}
+
+				return acc
+			}, {}),
+	)
+}

package.json

@@ -69,6 +69,7 @@
     "address": "^2.0.3",
     "bcryptjs": "^2.4.3",
     "better-sqlite3": "^11.1.2",
+    "cache-control-parser": "^2.0.6",
     "chalk": "^5.3.0",
     "class-variance-authority": "^0.7.0",
     "close-with-grace": "^1.3.0",