Function buildFileContentParts

packages/bot-telegram/src/download-files.ts:110–215

(
  files: TelegramFileRef[],
  token: string,
  getFilePath: (fileId: string) => Promise<string>,
  config: FileDeliveryConfig = {},
)

 * @param config     Optional delivery configuration.
 */
export async function buildFileContentParts(
  files: TelegramFileRef[],
  token: string,
  getFilePath: (fileId: string) => Promise<string>,
  config: FileDeliveryConfig = {},
): Promise<{ parts: AgentContentPart[]; notes: string[] }> {
  const maxBytes = config.maxBytesPerFile ?? DEFAULTS.maxBytesPerFile;
  const maxFiles = config.maxFiles ?? DEFAULTS.maxFiles;

  const parts: AgentContentPart[] = [];
  const notes: string[] = [];
  const considered = files.slice(0, maxFiles);
  if (files.length > maxFiles) {
    notes.push(
      `(only the first ${maxFiles} of ${files.length} files processed)`,
    );
  }

  for (const f of considered) {
    const label = f.fileName ?? f.fileId;
    const mime = (f.mimeType ?? "application/octet-stream").toLowerCase();

    if (typeof f.size === "number" && f.size > maxBytes) {
      notes.push(
        `skipped "${label}": ${f.size} bytes too large (cap is ${maxBytes} bytes)`,
      );
      continue;
    }

    let filePath: string;
    try {
      filePath = await getFilePath(f.fileId);
    } catch (err) {
      const msg = err instanceof Error ? err.message : String(err);
      notes.push(
        `skipped "${label}": could not resolve file path — ${redactToken(msg, token)}`,
      );
      continue;
    }

    const url = `https://api.telegram.org/file/bot${token}/${filePath}`;
    let bytes: Buffer;
    try {
      const res = await fetch(url);
      if (!res.ok) {
        notes.push(`skipped "${label}": download failed (HTTP ${res.status})`);
        continue;
      }

      // Pre-check Content-Length to avoid buffering oversized responses entirely
      // into memory (memory-DoS guard for cases where f.size is absent, e.g. photos).
      const contentLength = res.headers.get("content-length");
      if (contentLength !== null) {
        const declared = parseInt(contentLength, 10);
        if (!isNaN(declared) && declared > maxBytes) {
          notes.push(
            `skipped "${label}": Content-Length ${declared} bytes too large (cap is ${maxBytes} bytes)`,
          );