Function POST

apps/docs/app/api/chat/route.ts:278–344

(req: Request)

}

export async function POST(req: Request) {
  if (!isAllowedOrigin(req)) {
    return new Response('Forbidden', { status: 403 })
  }

  const now = Date.now()
  sweepRateLimit(now)
  const retryAfter = rateLimit(getClientIp(req), now)
  if (retryAfter !== null) {
    return new Response('Too many requests', {
      status: 429,
      headers: { 'Retry-After': String(retryAfter) },
    })
  }

  let body: { messages: UIMessage[]; locale?: string }
  try {
    body = await req.json()
  } catch {
    return new Response('Invalid JSON', { status: 400 })
  }
  const { messages } = body
  const locale = KNOWN_LOCALES.includes(body.locale ?? '')
    ? (body.locale as string)
    : DEFAULT_LOCALE

  if (!Array.isArray(messages) || messages.length === 0 || messages.length > MAX_MESSAGES) {
    return new Response('Invalid request', { status: 400 })
  }
  if (!messages.every(isValidMessage)) {
    return new Response('Invalid request', { status: 400 })
  }
  if (userInputChars(messages) > MAX_USER_INPUT_CHARS) {
    return new Response('Request too large', { status: 413 })
  }

  const modelMessages = sanitizeMessages(messages)
  if (modelMessages.length === 0) {
    return new Response('Invalid request', { status: 400 })
  }
  // Bound what actually reaches the model. Measured AFTER sanitization, so the
  // prior searchDocs tool outputs that accumulate in client history (and are
  // stripped here) don't count — only user/assistant text the model will see.
  if (JSON.stringify(modelMessages).length > MAX_TOTAL_CHARS) {
    return new Response('Request too large', { status: 413 })
  }

  const result = streamText({
    model: openai(CHAT_MODEL),
    system: SYSTEM_PROMPT,
    messages: convertToModelMessages(modelMessages),
    stopWhen: stepCountIs(MAX_STEPS),
    maxOutputTokens: MAX_OUTPUT_TOKENS,
    tools: {
      searchDocs: tool({
        description:
          'Search the Sim documentation for relevant content. Use this before answering any question about Sim.',
        inputSchema: z.object({