vercel/ai · error · UnsupportedFunctionalityError

AI_UnsupportedFunctionalityError

AI_UnsupportedFunctionalityError

Error message

'file part data type ${part.data.type}' functionality not supported.

What it means

formatImageUrl converts AI SDK file parts into data URLs for Alibaba messages. Only 'url' and 'data' (binary) part types are convertible; any other part.data.type (e.g. a new or provider-specific kind) reaches the final throw of UnsupportedFunctionalityError.

Source

Thrown at packages/alibaba/src/convert-to-alibaba-chat-messages.ts:23

} from '@ai-sdk/provider';
import {
  convertToBase64,
  getTopLevelMediaType,
  resolveFullMediaType,
} from '@ai-sdk/provider-utils';
import type { AlibabaChatPrompt } from './alibaba-chat-prompt';
import type { CacheControlValidator } from './get-cache-control';

function formatImageUrl({ part }: { part: LanguageModelV4FilePart }): string {
  if (part.data.type === 'url') {
    return part.data.url.toString();
  }

  if (part.data.type === 'data') {
    return `data:${resolveFullMediaType({ part })};base64,${convertToBase64(part.data.data)}`;
  }

  throw new UnsupportedFunctionalityError({
    functionality: `file part data type ${part.data.type}`,
  });
}

export function convertToAlibabaChatMessages({
  prompt,
  cacheControlValidator,
}: {
  prompt: LanguageModelV4Prompt;
  cacheControlValidator?: CacheControlValidator;
}): AlibabaChatPrompt {
  const messages: AlibabaChatPrompt = [];

  for (const { role, content, ...message } of prompt) {
    const messageCacheControl = cacheControlValidator?.getCacheControl(
      message.providerOptions,
    );

View on GitHub (pinned to 69428b1f8b)

Solutions

1. Send file parts with { type: 'url' } or raw binary { type: 'data' } (Uint8Array) instead
2. Strip or convert reference-type parts before the call
3. Update @ai-sdk/alibaba in case a newer core introduced the new part type

Example fix

// before
content: [{ type: 'file', data: { type: 'reference', reference: fileRef }, mediaType: 'image/png' }]
// after
content: [{ type: 'file', data: { type: 'url', url: 'https://.../img.png' }, mediaType: 'image/png' }]

prompt.forEach(m => m.content.forEach(p => {
  if (p.type === 'file' && p.data.type !== 'url' && p.data.type !== 'data') throw new Error('Unsupported file part data type');
}));

function isConvertibleFilePart(p: any): boolean {
  return p?.type === 'file' && (p.data?.type === 'url' || p.data?.type === 'data');
}

try {
  await streamText({ model: alibabaModel, messages });
} catch (e) {
  if (UnsupportedFunctionalityError.isInstance(e) && e.functionality.startsWith('file part data type')) {
    // rebuild messages with url/data file parts
  }
}

When it happens

Trigger: Passing a message file part whose data.type is neither 'url' nor 'data' — e.g. { type: 'reference' } routed through formatImageUrl or a future/unknown part kind — while converting the prompt for Alibaba chat.

Common situations: Forwarding provider-specific file references (e.g. from another provider's response) into an Alibaba request, or SDK version skew introducing new file part data types.

Related errors

• file parts with provider references
• File URL data
• media type: ${part.mediaType}
• file parts with provider references
• text file parts

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/3c3061697c041510. Report an issue: GitHub.