dropping file with unsupported media type '%s' (must be uplo

Error message

dropping file with unsupported media type '%s' (must be uploaded to Files API and sent as file_id)

What it means

The Anthropic converter only supports image/*, application/pdf, and text/plain media types for inline conversion. Any other media type (audio, video, zip, office docs, etc.) cannot be sent inline and must be uploaded to Anthropic's Files API and referenced by file_id, so the library rejects the part with this error rather than silently producing a bad block.

Source

Thrown at pkg/aiusechat/anthropic/anthropic-convertmessage.go:454

			if err != nil {
				return nil, fmt.Errorf("failed to decode base64 data: %w", err)
			}
			return &anthropicMessageContentBlock{
				Type: "document",
				Source: &anthropicSource{
					Type:      "text",
					Data:      string(textData),
					MediaType: "text/plain",
				},
			}, nil
		} else {
			// HTTP/HTTPS URL → not supported inline, would need to fetch
			return nil, fmt.Errorf("dropping text/plain file with URL (must be fetched and converted to base64 or uploaded to Files API)")
		}

	default:
		// Other media types → not supported inline, must upload and use file_id
		return nil, fmt.Errorf("dropping file with unsupported media type '%s' (must be uploaded to Files API and sent as file_id)", p.MediaType)
	}

}

// convertAIMessageToAnthropicChatMessage converts an AIMessage to anthropicChatMessage
// These messages are ALWAYS role "user"
func ConvertAIMessageToAnthropicChatMessage(aiMsg uctypes.AIMessage) (*anthropicChatMessage, error) {
	if err := aiMsg.Validate(); err != nil {
		return nil, fmt.Errorf("invalid AIMessage: %w", err)
	}

	var contentBlocks []anthropicMessageContentBlock

	for i, part := range aiMsg.Parts {
		switch part.Type {
		case uctypes.AIMessagePartTypeText:
			if part.Text == "" {
				return nil, fmt.Errorf("part %d: text type requires non-empty text field", i)

View on GitHub (pinned to a4447c1563)

Solutions

Upload the file to the Anthropic Files API and reference it via file_id in your request
Restrict accepted attachments to images, PDFs, and text before they reach the converter
Transcode non-image media into a supported representation (e.g. transcribe audio to text, convert docs to PDF/text)

Example fix

// before
part := uctypes.UIMessagePart{Type: "file", MediaType: "audio/mpeg", URL: dataURL}
// after
// transcribe or convert first
part := uctypes.UIMessagePart{Type: "file", MediaType: "text/plain", URL: "data:text/plain;base64," + base64.StdEncoding.EncodeToString(transcript)}

Defensive patterns

Strategy: validation

Validate before calling

func inlineSupported(mime string) bool {
    return strings.HasPrefix(mime, "image/") || mime == "application/pdf" || mime == "text/plain"
}
if !inlineSupported(p.MediaType) { /* upload to Files API or reject */ }

Type guard

func isInlineableMedia(mime string) bool {
    return strings.HasPrefix(mime, "image/") || mime == "application/pdf" || mime == "text/plain"
}

Try / catch

if err := convert(msg); err != nil {
    if strings.Contains(err.Error(), "unsupported media type") {
        fileID, uerr := uploadToAnthropicFiles(part)
        if uerr == nil { return convert(withFileID(msg, fileID)) }
    }
    return err
}

Prevention

Whitelist accepted attachment mime types at ingestion (image/*, application/pdf, text/plain)
Implement a Files API upload path for everything else
Convert/transcode audio, video, and office docs into supported formats before sending

When it happens

Trigger: Sending a UIMessagePart or AIMessagePart with Type "file" whose MediaType is e.g. audio/mpeg, video/mp4, application/zip, application/vnd.openxmlformats-officedocument.wordprocessingml.document — anything not image/*, application/pdf, or text/plain.

Common situations: Attaching audio/video recordings from a chat UI; sending Excel/Word/CSV(odd mime) attachments; forwarding arbitrary user uploads straight to the model without filtering.

Related errors

AI-assisted analysis of wavetermdev/waveterm@a4447c1563 (2026-09-01). Data as JSON: /api/errors/d4bf2b2a295ce234. Report an issue: GitHub.