docs: Ask AI chat grounded in the docs vector store

apps/docs/app/[lang]/layout.tsx

@@ -3,6 +3,7 @@ import { defineI18nUI } from 'fumadocs-ui/i18n'
 import { DocsLayout } from 'fumadocs-ui/layouts/docs'
 import { RootProvider } from 'fumadocs-ui/provider/next'
 import { Geist_Mono, Inter } from 'next/font/google'
+import { AskAI } from '@/components/ai/ask-ai'
 import {
   SidebarFolder,
   SidebarItem,
@@ -120,6 +121,7 @@ export default async function Layout({ children, params }: LayoutProps) {
           >
             {children}
           </DocsLayout>
+          <AskAI locale={lang} />
         </RootProvider>
       </body>
     </html>

apps/docs/app/api/chat/route.ts

@@ -0,0 +1,302 @@
+import { openai } from '@ai-sdk/openai'
+import { convertToModelMessages, stepCountIs, streamText, tool, type UIMessage } from 'ai'
+import { sql } from 'drizzle-orm'
+import { z } from 'zod'
+import { db, docsEmbeddings } from '@/lib/db'
+import { generateSearchEmbedding } from '@/lib/embeddings'
+
+export const runtime = 'nodejs'
+export const maxDuration = 30
+
+/** Model used for the Ask AI chat. Override with OPENAI_CHAT_MODEL in the environment. */
+const CHAT_MODEL = process.env.OPENAI_CHAT_MODEL || 'gpt-5.4-mini'
+
+/** Max documentation chunks returned per search to ground an answer. */
+const SEARCH_LIMIT = 6
+
+/** Candidates pulled before locale filtering, so a locale still yields SEARCH_LIMIT results. */
+const SEARCH_CANDIDATES = SEARCH_LIMIT * 4
+
+/** Minimum cosine similarity for an English vector match (mirrors the site search route). */
+const SIMILARITY_THRESHOLD = 0.6
+
+/** Locales the docs are published in (mirrors the site search route). */
+const KNOWN_LOCALES = ['en', 'es', 'fr', 'de', 'ja', 'zh']
+const DEFAULT_LOCALE = 'en'
+
+/** Postgres full-text config per locale (mirrors the site search route). */
+const TS_CONFIG: Record<string, string> = {
+  en: 'english',
+  es: 'spanish',
+  fr: 'french',
+  de: 'german',
+  ja: 'simple',
+  zh: 'simple',
+}
+
+/**
+ * Abuse guards. This endpoint proxies a paid LLM, so an unauthenticated public
+ * route is a target for scripted "free inference". These bounds cap the cost of
+ * any single request; an in-memory per-IP rate limit (below) caps volume on the
+ * hot path. A shared-store rate limit, a provider spend cap, and edge bot
+ * protection remain the durable controls (see the PR checklist).
+ *
+ * The size cap counts only user-authored text — NOT the conversation history,
+ * assistant turns, or retrieved doc chunks we add via the searchDocs tool, which
+ * legitimately grow large over a multi-turn chat.
+ */
+const MAX_MESSAGES = 200
+const MAX_USER_INPUT_CHARS = 400_000
+const MAX_OUTPUT_TOKENS = 4000
+const MAX_STEPS = 6
+/** Backstop on the whole serialized payload — blocks stuffing assistant/tool parts past the user-text cap. */
+const MAX_TOTAL_CHARS = 1_000_000
+
+/**
+ * Per-IP rate limit. Fixed window, in-memory: this bounds volume from a single
+ * source on a warm instance without external infra. It is best-effort on
+ * serverless (state is per-instance, not shared across regions/cold starts);
+ * a shared store (e.g. Vercel KV) and an edge WAF remain the durable controls,
+ * but this closes the "no volume limit at all" gap on the hot path.
+ */
+const RATE_LIMIT_MAX = 20
+const RATE_LIMIT_WINDOW_MS = 60_000
+const rateLimitHits = new Map<string, { count: number; resetAt: number }>()
+
+/** Resolve the client IP from forwarding headers, falling back to a shared bucket. */
+function getClientIp(req: Request): string {
+  const forwarded = req.headers.get('x-forwarded-for')
+  if (forwarded) return forwarded.split(',')[0].trim()
+  return req.headers.get('x-real-ip') ?? 'unknown'
+}
+
+/** Fixed-window check. Returns retry-after seconds when the caller is over the limit, else null. */
+function rateLimit(ip: string, now: number): number | null {
+  const entry = rateLimitHits.get(ip)
+  if (!entry || now >= entry.resetAt) {
+    rateLimitHits.set(ip, { count: 1, resetAt: now + RATE_LIMIT_WINDOW_MS })
+    return null
+  }
+  if (entry.count >= RATE_LIMIT_MAX) {
+    return Math.ceil((entry.resetAt - now) / 1000)
+  }
+  entry.count += 1
+  return null
+}
+
+/** Drop expired buckets so the Map doesn't grow unbounded on a long-lived instance. */
+function sweepRateLimit(now: number): void {
+  if (rateLimitHits.size < 10_000) return
+  for (const [ip, entry] of rateLimitHits) {
+    if (now >= entry.resetAt) rateLimitHits.delete(ip)
+  }
+}
+
+/** A structurally valid UI message: has a role and a parts array. */
+function isValidMessage(message: unknown): message is UIMessage {
+  return (
+    typeof message === 'object' &&
+    message !== null &&
+    typeof (message as { role?: unknown }).role === 'string' &&
+    Array.isArray((message as { parts?: unknown }).parts)
+  )
+}
+
+/** Total length of user-authored text across the conversation. */
+function userInputChars(messages: UIMessage[]): number {
+  let total = 0
+  for (const message of messages) {
+    if (message.role !== 'user') continue
+    for (const part of message.parts) {
+      if (part.type === 'text' && typeof part.text === 'string') total += part.text.length
+    }
+  }
+  return total
+}
+
+/**
+ * Strip everything the model shouldn't trust from client-supplied history:
+ * drop `system` messages (client-injected instructions) and every non-text part
+ * (e.g. crafted tool results faking searchDocs output). Only user/assistant text
+ * survives, so grounding comes from the server-run searchDocs tool — not the
+ * client's payload.
+ */
+function sanitizeMessages(messages: UIMessage[]): UIMessage[] {
+  return messages
+    .filter((message) => message.role === 'user' || message.role === 'assistant')
+    .map((message) => ({
+      ...message,
+      parts: message.parts.filter((part) => part.type === 'text' && typeof part.text === 'string'),
+    }))
+    .filter((message) => message.parts.length > 0)
+}
+
+/**
+ * Reject obvious cross-origin calls. Same-origin browser requests send an
+ * `Origin` header matching the host; we allow those, plus any host in
+ * DOCS_ALLOWED_ORIGINS (comma-separated). Requests with no Origin (e.g. curl)
+ * are allowed through to the cost caps rather than blocked, since Origin is
+ * trivially spoofable and is a filter, not a security boundary.
+ */
+function isAllowedOrigin(req: Request): boolean {
+  const origin = req.headers.get('origin')
+  if (!origin) return true
+
+  let originHost: string
+  try {
+    originHost = new URL(origin).host.toLowerCase()
+  } catch {
+    return false
+  }
+
+  const forwardedHost = req.headers.get('x-forwarded-host') ?? req.headers.get('host')
+  const requestHost = forwardedHost?.split(',')[0].trim().toLowerCase()
+  if (requestHost && originHost === requestHost) return true
+
+  const allowlist = (process.env.DOCS_ALLOWED_ORIGINS ?? '')
+    .split(',')
+    .map((value) => value.trim().toLowerCase())
+    .filter(Boolean)
+  return allowlist.includes(originHost)
+}
+
+const SYSTEM_PROMPT = `You are the documentation assistant for Sim — the open-source AI workspace where teams build, deploy, and manage AI agents.
+
+Answer questions about Sim using the documentation. Always call the searchDocs tool before answering anything specific about Sim's features, configuration, or usage — do not answer from memory. Base your answer only on the returned documentation; if the docs do not cover the question, say so plainly rather than guessing.
+
+Guidelines:
+- Be direct and concrete. Lead with the answer, then the detail.
+- Reference the relevant pages by their titles so the user knows where to read more.
+- When you show configuration or code, keep it minimal and correct.
+- The agent is called "Sim" and the chat surface is "Chat" — never say "Mothership" or "copilot".
+- If a question is unrelated to Sim, briefly say it's outside the docs' scope.`
+
+const SEARCH_COLUMNS = {
+  title: docsEmbeddings.headerText,
+  url: docsEmbeddings.sourceLink,
+  content: docsEmbeddings.chunkText,
+  sourceDocument: docsEmbeddings.sourceDocument,
+}
+
+/**
+ * Retrieve candidate chunks for grounding. English docs are embedded, so they
+ * use vector similarity; other locales rely on Postgres full-text keyword search
+ * (vector search over English-trained embeddings does not serve them) — the same
+ * split the site search route makes.
+ */
+/**
+ * SQL predicate selecting only the locale's documents, so the row limit applies
+ * to matching rows (mirrors `matchesLocale`): non-English docs are prefixed with
+ * their locale segment; English is everything not prefixed with another locale.
+ */
+function localeFilter(locale: string) {
+  const firstSegment = sql`split_part(${docsEmbeddings.sourceDocument}, '/', 1)`
+  if (locale === DEFAULT_LOCALE) {
+    const others = KNOWN_LOCALES.filter((l) => l !== DEFAULT_LOCALE)
+    return sql`${firstSegment} not in (${sql.join(
+      others.map((l) => sql`${l}`),
+      sql`, `
+    )})`
+  }
+  return sql`${firstSegment} = ${locale}`
+}
+
+async function searchDocs(query: string, locale: string) {
+  let rows: Array<{ title: string; url: string; content: string; sourceDocument: string }>
+
+  if (locale === DEFAULT_LOCALE) {
+    const embedding = await generateSearchEmbedding(query)
+    const vectorLiteral = JSON.stringify(embedding)
+    rows = await db
+      .select(SEARCH_COLUMNS)
+      .from(docsEmbeddings)
+      .where(
+        sql`1 - (${docsEmbeddings.embedding} <=> ${vectorLiteral}::vector) >= ${SIMILARITY_THRESHOLD} and ${localeFilter(locale)}`
+      )
+      .orderBy(sql`${docsEmbeddings.embedding} <=> ${vectorLiteral}::vector`)
+      .limit(SEARCH_CANDIDATES)
+  } else {
+    const tsConfig = TS_CONFIG[locale] ?? 'simple'
+    rows = await db
+      .select(SEARCH_COLUMNS)
+      .from(docsEmbeddings)
+      .where(
+        sql`${docsEmbeddings.chunkTextTsv} @@ plainto_tsquery(${tsConfig}, ${query}) and ${localeFilter(locale)}`
+      )
+      .orderBy(
+        sql`ts_rank(${docsEmbeddings.chunkTextTsv}, plainto_tsquery(${tsConfig}, ${query})) DESC`
+      )
+      .limit(SEARCH_CANDIDATES)
+  }
+
+  return rows.slice(0, SEARCH_LIMIT).map((row) => ({
+    title: row.title,
+    url: row.url,
+    content: row.content,
+  }))
+}
+
+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 })
+  }
+  if (JSON.stringify(messages).length > MAX_TOTAL_CHARS) {
+    return new Response('Request too large', { status: 413 })
+  }
+
+  const modelMessages = sanitizeMessages(messages)
+  if (modelMessages.length === 0) {
+    return new Response('Invalid request', { status: 400 })
+  }
+
+  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({
+          query: z.string().describe('A focused natural-language search query.'),
+        }),
+        execute: async ({ query }) => searchDocs(query, locale),
+      }),
+    },
+  })
+
+  return result.toUIMessageStreamResponse()
+}