freezmo/app/api/sync/route.ts

import { promises as fs } from "node:fs";
import path from "node:path";
import { z } from "zod";

import { authErrorKind, authErrorMessage, getServerConfig, resolveAuth } from "@/lib/config";
import { rejectCrossOrigin, rejectOversizedBody, requestLocale } from "@/lib/http-guard";
import { translate } from "@/lib/i18n-dict";
import { clientKey, rateLimit, rateLimitResponse } from "@/lib/rate-limit";

export const runtime = "nodejs";
export const dynamic = "force-dynamic";

/**
 * Opt-in encrypted sync storage. The server only ever sees:
 *  - a random sync ID (the capability)
 *  - an opaque AES-GCM envelope (salt, iv, ciphertext) and a server timestamp
 * It cannot read the data and never receives the passphrase or API key.
 */

const idSchema = z.string().regex(/^[A-Za-z0-9_-]{16,64}$/);

const envelopeSchema = z.object({
  v: z.literal(1),
  kdf: z.literal("PBKDF2-SHA256"),
  iterations: z.number().int().min(50_000).max(2_000_000),
  salt: z.string().min(8).max(128),
  iv: z.string().min(8).max(64),
  ciphertext: z.string().min(1).max(24_000_000),
});

const postSchema = z.object({ id: idSchema, envelope: envelopeSchema });

function fileFor(dir: string, id: string): string {
  return path.join(dir, `${id}.json`);
}

async function writeAtomic(file: string, data: string): Promise<void> {
  await fs.mkdir(path.dirname(file), { recursive: true });
  const temporary = `${file}.${crypto.randomUUID()}.tmp`;
  await fs.writeFile(temporary, data, "utf8");
  await fs.rename(temporary, file);
}

/** Size of all stored blobs except `exclude` (the one being replaced). */
async function directoryBytes(dir: string, exclude: string): Promise<number> {
  let total = 0;
  try {
    for (const entry of await fs.readdir(dir)) {
      if (!entry.endsWith(".json")) continue;
      const full = path.join(dir, entry);
      if (full === exclude) continue;
      try {
        total += (await fs.stat(full)).size;
      } catch {
        /* deleted meanwhile */
      }
    }
  } catch {
    /* directory doesn't exist yet */
  }
  return total;
}

export async function GET(request: Request) {
  const locale = requestLocale(request);
  const crossOrigin = rejectCrossOrigin(request);
  if (crossOrigin) return crossOrigin;

  const config = getServerConfig();
  const limit = rateLimit(`sync:${clientKey(request)}`, config.rateLimits.sync, config.rateLimits.windowMs);
  if (!limit.allowed) return rateLimitResponse(limit, locale);

  const auth = resolveAuth(config, request);
  if ("error" in auth) {
    return Response.json(
      { error: authErrorMessage(locale, auth.error), kind: authErrorKind(auth.error) },
      { status: 401 },
    );
  }

  const id = new URL(request.url).searchParams.get("id") ?? "";
  if (!idSchema.safeParse(id).success) {
    return Response.json(
      { error: translate(locale, "server.syncInvalidId") },
      { status: 400, headers: { "Cache-Control": "no-store" } },
    );
  }

  try {
    const raw = await fs.readFile(fileFor(config.sync.dir, id), "utf8");
    return new Response(raw, {
      status: 200,
      headers: { "Content-Type": "application/json", "Cache-Control": "no-store" },
    });
  } catch {
    return Response.json(
      { error: translate(locale, "server.syncNotFound") },
      { status: 404, headers: { "Cache-Control": "no-store" } },
    );
  }
}

export async function POST(request: Request) {
  const locale = requestLocale(request);
  const crossOrigin = rejectCrossOrigin(request);
  if (crossOrigin) return crossOrigin;

  const config = getServerConfig();
  const oversized = rejectOversizedBody(request, config.sync.maxBytes);
  if (oversized) return oversized;

  const limit = rateLimit(`sync:${clientKey(request)}`, config.rateLimits.sync, config.rateLimits.windowMs);
  if (!limit.allowed) return rateLimitResponse(limit, locale);

  // Auth before parsing the body, like every other route.
  const auth = resolveAuth(config, request);
  if ("error" in auth) {
    return Response.json(
      { error: authErrorMessage(locale, auth.error), kind: authErrorKind(auth.error) },
      { status: 401 },
    );
  }

  let payload: unknown;
  try {
    payload = await request.json();
  } catch {
    return Response.json({ error: translate(locale, "server.bodyNotJson") }, { status: 400 });
  }

  const parsed = postSchema.safeParse(payload);
  if (!parsed.success) {
    return Response.json(
      {
        error: translate(locale, "server.invalidRequest", {
          detail: parsed.error.issues
            .slice(0, 3)
            .map((issue) => `${issue.path.join(".") || "body"} ${issue.message}`)
            .join("; "),
        }),
      },
      { status: 400 },
    );
  }

  const file = fileFor(config.sync.dir, parsed.data.id);
  const serialised = JSON.stringify({ updatedAt: Date.now(), envelope: parsed.data.envelope });

  // Total storage cap, checked only when a new blob is created.
  const exists = await fs
    .stat(file)
    .then(() => true)
    .catch(() => false);
  if (!exists) {
    const used = await directoryBytes(config.sync.dir, file);
    if (used + serialised.length > config.sync.totalBytes) {
      return Response.json(
        { error: translate(locale, "server.syncStorageFull"), kind: "storage_full" },
        { status: 507 },
      );
    }
  }

  await writeAtomic(file, serialised);
  const updatedAt = (JSON.parse(serialised) as { updatedAt: number }).updatedAt;
  return Response.json({ updatedAt }, { headers: { "Cache-Control": "no-store" } });
}

export async function DELETE(request: Request) {
  const locale = requestLocale(request);
  const crossOrigin = rejectCrossOrigin(request);
  if (crossOrigin) return crossOrigin;

  const config = getServerConfig();
  const limit = rateLimit(`sync:${clientKey(request)}`, config.rateLimits.sync, config.rateLimits.windowMs);
  if (!limit.allowed) return rateLimitResponse(limit, locale);

  const auth = resolveAuth(config, request);
  if ("error" in auth) {
    return Response.json(
      { error: authErrorMessage(locale, auth.error), kind: authErrorKind(auth.error) },
      { status: 401 },
    );
  }

  const id = new URL(request.url).searchParams.get("id") ?? "";
  if (!idSchema.safeParse(id).success) {
    return Response.json(
      { error: translate(locale, "server.syncInvalidId") },
      { status: 400, headers: { "Cache-Control": "no-store" } },
    );
  }

  await fs.unlink(fileFor(config.sync.dir, id)).catch(() => {});
  return Response.json({ ok: true }, { headers: { "Cache-Control": "no-store" } });
}