vercel/ai · error · InvalidArgumentError

DeepSeek filenames must not exceed ${MAX_FILENAME_LENGTH} ch

Error message

DeepSeek filenames must not exceed ${MAX_FILENAME_LENGTH} characters. Received ${filenameLength} characters.

What it means

DeepSeek enforces a maximum filename length (MAX_FILENAME_LENGTH). The length is counted in Unicode code points (Array.from(filename).length, not UTF-8 bytes) and an over-long filename throws InvalidArgumentError for argument 'filename' before any network call.

Source

Thrown at packages/deepseek/src/files/deepseek-files.ts:167

  fileBytes: Uint8Array;
  mediaType: string;
  filename: string | undefined;
}) {
  if (fileBytes.length > MAX_FILE_SIZE_BYTES) {
    throw new InvalidArgumentError({
      argument: 'data',
      message:
        `DeepSeek file uploads must not exceed 64 MiB ` +
        `(${MAX_FILE_SIZE_BYTES.toLocaleString('en-US')} bytes). ` +
        `Received ${fileBytes.length.toLocaleString('en-US')} bytes.`,
    });
  }

  if (filename != null) {
    const filenameLength = Array.from(filename).length;

    if (filenameLength > MAX_FILENAME_LENGTH) {
      throw new InvalidArgumentError({
        argument: 'filename',
        message:
          `DeepSeek filenames must not exceed ${MAX_FILENAME_LENGTH} characters. ` +
          `Received ${filenameLength} characters.`,
      });
    }
  }

  const normalizedMediaType = normalizeMediaType(mediaType);
  const detectedMediaType = detectMediaType({ data: fileBytes });

  if (
    detectedMediaType != null &&
    !supportedMediaTypes.has(detectedMediaType)
  ) {
    throw new InvalidArgumentError({
      argument: 'data',
      message:

View on GitHub (pinned to 69428b1f8b)

Solutions

Truncate the filename (keeping the extension) before uploading.
Generate a short synthetic filename (e.g. 'upload-<hash8>.png') when the original name is very long.
Sanitize inputs: strip directory paths and limit the name length to the documented max.

Example fix

// before
await files.upload({ data, mediaType: 'image/png', filename: veryLongName });

// after
const base = veryLongName.split('/').pop() ?? 'file.png';
const filename = base.length > 128 ? base.slice(0, 100) + base.slice(base.lastIndexOf('.')) : base;
await files.upload({ data, mediaType: 'image/png', filename });

Defensive patterns

Strategy: validation

Validate before calling

if (filename && Array.from(filename).length > 128) {
  filename = filename.slice(0, 100) + (filename.match(/\.[a-z0-9]+$/i)?.[0] ?? '');
}

Try / catch

import { InvalidArgumentError } from '@ai-sdk/provider';
try {
  await files.upload({ data, mediaType, filename });
} catch (e) {
  if (InvalidArgumentError.isInstance(e) && e.argument === 'filename') {
    await files.upload({ data, mediaType, filename: truncateName(filename) });
  } else throw e;
}

Prevention

Strip paths and generate short names server-side instead of trusting client filenames.
Count length in code points (Array.from), matching the library's check.
Sanitize filenames in a shared upload utility used by all call sites.

When it happens

Trigger: Uploading a file whose filename string exceeds MAX_FILENAME_LENGTH code points via deepseek.files.upload with a filename provided.

Common situations: Passing long auto-generated names (timestamps + hashes + descriptions), or forwarding the full path or data-URI as the filename instead of the basename.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/ce8295bab33e0412. Report an issue: GitHub.