fix(posthog): replace proxy rewrite with route handler for reliable body streaming

apps/sim/app/ingest/[[...path]]/route.ts

@@ -0,0 +1,73 @@
+import { createLogger } from '@sim/logger'
+import { type NextRequest, NextResponse } from 'next/server'
+
+const logger = createLogger('PostHogProxy')
+
+const API_HOST = 'us.i.posthog.com'
+const ASSET_HOST = 'us-assets.i.posthog.com'
+
+/**
+ * Builds the target PostHog URL from the incoming request path.
+ * Routes /ingest/static/* to the asset host, everything else to the API host.
+ */
+function buildTargetUrl(pathname: string, search: string): { url: string; hostname: string } {
+  const strippedPath = pathname.replace(/^\/ingest/, '')
+  const hostname = strippedPath.startsWith('/static/') ? ASSET_HOST : API_HOST
+  return {
+    url: `https://${hostname}${strippedPath}${search}`,
+    hostname,
+  }
+}
+
+/**
+ * Builds forwarding headers for the PostHog request.
+ * Sets the Host header and strips cookies/connection headers
+ * that shouldn't be forwarded.
+ */
+function buildHeaders(request: NextRequest, hostname: string): Headers {
+  const headers = new Headers(request.headers)
+  headers.set('host', hostname)
+  headers.delete('cookie')
+  headers.delete('connection')
+
+  return headers
+}
+
+async function handler(request: NextRequest) {
+  const { url, hostname } = buildTargetUrl(request.nextUrl.pathname, request.nextUrl.search)
+  const headers = buildHeaders(request, hostname)
+
+  const hasBody = !['GET', 'HEAD'].includes(request.method)
+
+  try {
+    const response = await fetch(url, {
+      method: request.method,
+      headers,
+      ...(hasBody ? { body: request.body, duplex: 'half' } : {}),
+    } as RequestInit)
+
+    const responseHeaders = new Headers(response.headers)
+    responseHeaders.delete('content-encoding')
+    responseHeaders.delete('content-length')
+    responseHeaders.delete('transfer-encoding')
+
+    return new NextResponse(response.body, {
+      status: response.status,
+      headers: responseHeaders,
+    })
+  } catch (error) {
+    logger.error('PostHog proxy error', {
+      url,
+      method: request.method,
+      error: error instanceof Error ? error.message : String(error),
+    })
+    return new NextResponse(null, { status: 502 })
+  }
+}
+
+export const GET = handler
+export const POST = handler
+export const PUT = handler
+export const PATCH = handler
+export const DELETE = handler
+export const OPTIONS = handler

apps/sim/proxy.ts

@@ -140,24 +140,6 @@ function handleSecurityFiltering(request: NextRequest): NextResponse | null {
 export async function proxy(request: NextRequest) {
   const url = request.nextUrl
 
-  if (url.pathname.startsWith('/ingest/')) {
-    const hostname = url.pathname.startsWith('/ingest/static/')
-      ? 'us-assets.i.posthog.com'
-      : 'us.i.posthog.com'
-
-    const targetPath = url.pathname.replace(/^\/ingest/, '')
-    const targetUrl = `https://${hostname}${targetPath}${url.search}`
-
-    return NextResponse.rewrite(new URL(targetUrl), {
-      request: {
-        headers: new Headers({
-          ...Object.fromEntries(request.headers),
-          host: hostname,
-        }),
-      },
-    })
-  }
-
   const sessionCookie = getSessionCookie(request)
   const hasActiveSession = isAuthDisabled || !!sessionCookie
 
@@ -219,7 +201,6 @@ export async function proxy(request: NextRequest) {
 
 export const config = {
   matcher: [
-    '/ingest/:path*', // PostHog proxy for session recording
     '/', // Root path for self-hosted redirect logic
     '/terms', // Whitelabel terms redirect
     '/privacy', // Whitelabel privacy redirect
@@ -230,6 +211,6 @@ export const config = {
     '/signup',
     '/invite/:path*', // Match invitation routes
     // Catch-all for other pages, excluding static assets and public directories
-    '/((?!_next/static|_next/image|favicon.ico|logo/|static/|footer/|social/|enterprise/|favicon/|twitter/|robots.txt|sitemap.xml).*)',
+    '/((?!_next/static|_next/image|ingest|favicon.ico|logo/|static/|footer/|social/|enterprise/|favicon/|twitter/|robots.txt|sitemap.xml).*)',
   ],
 }