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Remove Server Action forwarding #96951

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146 changes: 3 additions & 143 deletions packages/next/src/server/app-render/action-handler.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,6 @@ import {
import { getModifiedCookieValues } from '../web/spec-extension/adapters/request-cookies'

import {
JSON_CONTENT_TYPE_HEADER,
NEXT_CACHE_REVALIDATED_TAGS_HEADER,
NEXT_CACHE_REVALIDATE_TAG_TOKEN_HEADER,
} from '../../lib/constants'
Expand All @@ -52,7 +51,6 @@ import { RequestCookies, ResponseCookies } from '../web/spec-extension/cookies'
import { HeadersAdapter } from '../web/spec-extension/adapters/headers'
import { fromNodeOutgoingHttpHeaders } from '../web/utils'
import {
selectWorkerForForwarding,
type ServerModuleMap,
getServerActionsManifest,
getServerModuleMap,
Expand Down Expand Up @@ -204,119 +202,6 @@ function addRevalidationHeader(
}
}

/**
* Forwards a server action request to a separate worker. Used when the requested action is not available in the current worker.
*/
async function createForwardedActionResponse(
req: BaseNextRequest,
res: BaseNextResponse,
host: Host,
workerPathname: string,
basePath: string
) {
if (!host) {
throw new Error(
'Invariant: Missing `host` header from a forwarded Server Actions request.'
)
}

const forwardedHeaders = getForwardedHeaders(req, res)

// indicate that this action request was forwarded from another worker
// we use this to skip rendering the flight tree so that we don't update the UI
// with the response from the forwarded worker
forwardedHeaders.set('x-action-forwarded', '1')

// TODO: Remove __NEXT_PRIVATE_ORIGIN
let origin: string | undefined = process.env.__NEXT_PRIVATE_ORIGIN
if (origin === undefined) {
const initUrl = getRequestMeta(req, 'initURL')
if (initUrl !== undefined) {
try {
const parsedUrl = new URL(initUrl)
origin = parsedUrl.origin
} catch (error) {
throw new Error(
'Could not determine origin for forwarded Server Actions request. This can happen if port or hostname are not configured for this server.',
{ cause: error }
)
}
} else {
throw new InvariantError('Missing initURL')
}
}

const fetchUrl = new URL(`${origin}${basePath}${workerPathname}`)

try {
let body: BodyInit | ReadableStream<Uint8Array> | undefined
if (
// The type check here ensures that `req` is correctly typed, and the
// environment variable check provides dead code elimination.
process.env.NEXT_RUNTIME === 'edge' &&
isWebNextRequest(req)
) {
if (!req.body) {
throw new Error('Invariant: missing request body.')
}

body = req.body
} else if (
// The type check here ensures that `req` is correctly typed, and the
// environment variable check provides dead code elimination.
process.env.NEXT_RUNTIME !== 'edge' &&
isNodeNextRequest(req)
) {
body = req.stream()
} else {
throw new Error('Invariant: Unknown request type.')
}

// Forward the request to the new worker
const response = await fetch(fetchUrl, {
method: 'POST',
body,
duplex: 'half',
headers: forwardedHeaders,
redirect: 'manual',
next: {
// @ts-ignore
internal: 1,
},
})

if (
response.headers.get('content-type')?.startsWith(RSC_CONTENT_TYPE_HEADER)
) {
// copy the headers from the redirect response to the response we're sending
for (const [key, value] of response.headers) {
if (!actionsForbiddenHeaders.includes(key)) {
res.setHeader(key, value)
}
}

return new FlightRenderResult(response.body!)
}

// Since we aren't consuming the response body, we cancel it to avoid memory leaks
response.body?.cancel()

// Pass the action-not-found marker through so the client throws
// UnrecognizedActionError instead of a generic "unexpected response".
if (response.headers.get(NEXT_ACTION_NOT_FOUND_HEADER) === '1') {
res.setHeader(NEXT_ACTION_NOT_FOUND_HEADER, '1')
res.setHeader('content-type', 'text/plain')
res.statusCode = 404
return RenderResult.fromStatic('Server action not found.', 'text/plain')
}
} catch (err) {
// we couldn't stream the forwarded response, so we'll just return an empty response
console.error(`failed to forward action response`, err)
}

return RenderResult.fromStatic('{}', JSON_CONTENT_TYPE_HEADER)
}

/**
* Returns the parsed redirect URL if we deem that it is hosted by us.
*
Expand Down Expand Up @@ -600,7 +485,6 @@ export async function handleAction({
metadata: AppPageRenderResultMetadata
}): Promise<HandleActionResult> {
const contentType = req.headers['content-type']
const { page } = ctx.renderOpts
const serverModuleMap = getServerModuleMap()

const {
Expand Down Expand Up @@ -754,7 +638,6 @@ export async function handleAction({
'no-cache, no-store, max-age=0, must-revalidate'
)

const actionWasForwarded = Boolean(req.headers['x-action-forwarded'])
// A fetch action without a router state tree cannot produce a Flight patch
// for the currently rendered page. This occurs when the client dispatches an
// action directly to a different route, so only execute the action without
Expand All @@ -768,30 +651,7 @@ export async function handleAction({
requestStore.fallbackParams != null &&
typeof ctx.renderOpts.postponed === 'string'
const shouldSkipPageRendering =
actionWasForwarded || isActionOnlyRequest || isActionOnlyFallbackRequest

// Only attempt to forward if this request has not already been forwarded.
// Otherwise middleware that rewrites the action POST can cause the receiving
// worker to forward again, looping indefinitely.
if (actionId && !actionWasForwarded) {
const forwardedWorker = selectWorkerForForwarding(actionId, page)

// If forwardedWorker is truthy, it means there isn't a worker for the
// action in the current handler, so we forward the request to a worker that
// has the action.
if (forwardedWorker) {
return {
type: 'done',
result: await createForwardedActionResponse(
req,
res,
host,
forwardedWorker,
ctx.renderOpts.basePath
),
}
}
}
isActionOnlyRequest || isActionOnlyFallbackRequest

@vercel vercel Bot Aug 8, 2026

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Removing Server Action forwarding breaks invoking a server action obtained indirectly at runtime (returned from another action) from a route that does not register that action, causing "Failed to find Server Action"/404 instead of executing it.

Fix on Vercel


try {
return await actionAsyncStorage.run(
Expand Down Expand Up @@ -906,7 +766,7 @@ export async function handleAction({
[],
workStore,
requestStore,
actionWasForwarded
false
)

const formState = await decodeFormState(
Expand Down Expand Up @@ -1115,7 +975,7 @@ export async function handleAction({
[],
workStore,
requestStore,
actionWasForwarded
false
)

const formState = await decodeFormState(
Expand Down
37 changes: 0 additions & 37 deletions packages/next/src/server/app-render/manifests-singleton.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@ import type { DeepReadonly } from '../../shared/lib/deep-readonly'
import { InvariantError } from '../../shared/lib/invariant-error'
import { normalizeAppPath } from '../../shared/lib/router/utils/app-paths'
import { pathHasPrefix } from '../../shared/lib/router/utils/path-has-prefix'
import { removePathPrefix } from '../../shared/lib/router/utils/remove-path-prefix'
import { mightBeServerReferenceId } from '../../shared/lib/server-reference-info'
import { wellKnownProperties } from '../../shared/lib/utils/reflect-utils'
import { createServerActionRoutingKey } from '../../shared/lib/server-action-routing-key'
Expand Down Expand Up @@ -301,42 +300,6 @@ function normalizeWorkerPageName(pageName: string) {
return 'app' + pageName
}

/**
* Converts a bundlePath (relative path to the entrypoint) to a routable page
* name.
*/
function denormalizeWorkerPageName(bundlePath: string) {
return normalizeAppPath(removePathPrefix(bundlePath, 'app'))
}

/**
* Checks if the requested action has a worker for the current page.
* If not, it returns the first worker that has a handler for the action.
*/
export function selectWorkerForForwarding(
actionId: string,
pageName: string
): string | undefined {
const serverActionsManifest = getServerActionsManifest()
const workers =
serverActionsManifest[
process.env.NEXT_RUNTIME === 'edge' ? 'edge' : 'node'
][actionId]?.workers

// There are no workers to handle this action, nothing to forward to.
if (!workers) {
return
}

// If there is an entry for the current page, we don't need to forward.
if (workers[normalizeWorkerPageName(pageName)]) {
return
}

// Otherwise, grab the first worker that has a handler for this action id.
return denormalizeWorkerPageName(Object.keys(workers)[0])
}

export function getServerActionRoutingKeysForPage(
pageName: string
): readonly string[] | undefined {
Expand Down
41 changes: 37 additions & 4 deletions test/e2e/app-dir/actions/app-action.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -917,7 +917,12 @@ describe('app-dir action handling', () => {
const cliOutputIndex = next.cliOutput.length
const browser = await next.browser(`/delayed-action/${runtime}`)
const actionRequestPaths: string[] = []
let actionRequestHeaders: Record<string, string> | undefined
let actionRequest:
| {
headers: Record<string, string>
body: string | null
}
| undefined

browser.on('request', (request) => {
const headers = request.headers()
Expand All @@ -926,7 +931,10 @@ describe('app-dir action handling', () => {
headers['next-action'] !== undefined
) {
actionRequestPaths.push(new URL(request.url()).pathname)
actionRequestHeaders = headers
actionRequest = {
headers,
body: request.postData(),
}
}
})

Expand Down Expand Up @@ -958,13 +966,38 @@ describe('app-dir action handling', () => {
expect(await browser.hasElementByCssSelector('#other-page')).toBe(true)

expect(actionRequestPaths).toEqual([`/delayed-action/${runtime}`])
expect(actionRequestHeaders?.['next-action-only']).toBeUndefined()
expect(actionRequestHeaders?.['next-router-state-tree']).toBeUndefined()
expect(actionRequest?.headers['next-action-only']).toBeUndefined()
expect(actionRequest?.headers['next-router-state-tree']).toBeUndefined()

// make sure we didn't get any errors in the console
expect(next.cliOutput.slice(cliOutputIndex)).not.toContain(
'Failed to find Server Action'
)

if (actionRequest === undefined) {
throw new Error('Failed to capture Server Action request')
}

// A valid action sent to the wrong route must fail instead of being
// forwarded to a route that bundles it.
const wronglyRoutedResponse = await next.fetch(
`/delayed-action/${runtime}/other`,
{
method: 'POST',
headers: {
accept: actionRequest.headers.accept,
'content-type': actionRequest.headers['content-type'],
'next-action': actionRequest.headers['next-action'],
origin: next.url,
},
body: actionRequest.body,
}
)

expect(wronglyRoutedResponse.status).toBe(404)
expect(
wronglyRoutedResponse.headers.get('x-nextjs-action-not-found')
).toBe('1')
}
)

Expand Down
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