gerbeur/api/routes/files.ts

import { Router } from "@oak/oak";
import { APIErrorCode } from "../../shared/api.ts";
import { APIException } from "../lib/api-exception.ts";
import { DUMPS_DIR } from "../lib/upload.ts";
import { authenticateMedia } from "../lib/auth.ts";
import { serveFile } from "../lib/serve-file.ts";
import { dumpFileVersion, getDump } from "../services/dump-service.ts";

const router = new Router({ prefix: "/api/files" });

/**
 * Builds an RFC 6266 `Content-Disposition` value that is always a valid
 * ByteString. `headers.set` throws a TypeError if the value contains any
 * character > U+00FF, so a filename with an emoji / accent / CJK character
 * (e.g. an uploaded file) would otherwise crash the response. We provide an
 * ASCII-only `filename="…"` fallback plus an RFC 5987 `filename*` with the
 * full UTF-8 name for modern browsers.
 */
function contentDisposition(
  type: "inline" | "attachment",
  name: string,
): string {
  const asciiFallback = name
    .replace(/["\\]/g, "_")
    .replace(/[^\x20-\x7e]/g, "_");
  return `${type}; filename="${asciiFallback}"; filename*=UTF-8''${
    encodeURIComponent(name)
  }`;
}

// The MIME type of an upload is whatever the uploader's browser claimed, and
// these responses come from the app's own origin — where the session token
// lives. Only types a browser renders without running the file's own code are
// served inline; anything else (text/html, image/svg+xml, XML, …) downloads.
// <img>, <audio> and fetch() ignore Content-Disposition, so previews that embed
// or read the file still work.
const INLINE_MIME_RE =
  /^(image\/(png|jpeg|gif|webp|avif|bmp)|audio\/[\w.+-]+|video\/[\w.+-]+|application\/pdf|text\/plain)$/;

function isInlineSafe(mime: string): boolean {
  return INLINE_MIME_RE.test(mime.split(";")[0].trim().toLowerCase());
}

router.get("/:dumpId", async (ctx) => {
  const { dumpId } = ctx.params;

  // Guard against path traversal (UUIDs are safe, but be explicit)
  if (!/^[0-9a-f-]{36}$/.test(dumpId)) {
    throw new APIException(APIErrorCode.BAD_REQUEST, 400, "Invalid dump ID");
  }

  // Media elements can't send an Authorization header, so the viewer's token
  // arrives as a query param (same as the WebSocket route). Needed to authorize
  // access to private dumps the requester owns.
  const token = ctx.request.url.searchParams.get("token");
  const viewerId = token ? await authenticateMedia(token) : null;
  const dump = getDump(dumpId, viewerId ?? undefined);

  if (dump.kind !== "file" || !dump.fileMime || !dump.fileName) {
    throw new APIException(
      APIErrorCode.NOT_FOUND,
      404,
      "No file for this dump",
    );
  }

  const path = `${DUMPS_DIR}/${dumpId}`;
  const inline = isInlineSafe(dump.fileMime);
  ctx.response.headers.set(
    "Content-Disposition",
    contentDisposition(inline ? "inline" : "attachment", dump.fileName),
  );
  ctx.response.headers.set("X-Content-Type-Options", "nosniff");
  // Belt and braces for a file opened directly: no scripts, no plugins, no
  // same-origin access. Chrome won't render a PDF in a sandboxed document, and
  // its viewer never runs a PDF's scripts anyway, so PDFs go without.
  if (dump.fileMime !== "application/pdf") {
    ctx.response.headers.set(
      "Content-Security-Policy",
      "sandbox; default-src 'none'; img-src 'self'; media-src 'self'; style-src 'unsafe-inline'",
    );
  }
  // The URL may carry a media token; don't pass it on to wherever the file
  // links.
  ctx.response.headers.set("Referrer-Policy", "no-referrer");

  // The app's URLs carry the file's version (see dumpFileVersion), so one
  // naming the current version never changes and is cached for good; any
  // other URL is revalidated against the ETag. A private dump's bytes must not
  // sit in a shared cache.
  const scope = dump.isPrivate ? "private" : "public";
  const current = ctx.request.url.searchParams.get("v") ===
    dumpFileVersion(dump);
  const served = await serveFile(ctx, path, {
    mime: dump.fileMime,
    cacheControl: current
      ? `${scope}, max-age=31536000, immutable`
      : `${scope}, no-cache`,
    ranges: true,
  });
  if (!served) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "File not found");
  }
});

export default router;