Tencent/WeKnora · error

attachment exceeds the %d MiB limit

Error message

attachment exceeds the %d MiB limit

What it means

prepareIMAttachments in internal/im/service.go rejects incoming file/image messages whose declared msg.FileSize exceeds maxIMAttachmentBytes before any download happens. The limit is reported in MiB (maxIMAttachmentBytes>>20). This is an early, cheap guard so oversized uploads never hit network I/O.

Source

Thrown at internal/im/service.go:610

		Channel:     "im",
		Attachments: messageAttachments,
	}
}

type imDownloadedAttachment struct {
	fileName string
	content  []byte
}

// prepareIMAttachments downloads an IM attachment and exposes its parsed text
// (and, for images, a bounded data URI) to the QA pipeline. This is separate
// from the optional background knowledge-base save.
func (s *Service) prepareIMAttachments(ctx context.Context, msg *IncomingMessage, adapter Adapter) (types.MessageAttachments, []string, *imDownloadedAttachment, error) {
	if msg.MessageType != MessageTypeFile && msg.MessageType != MessageTypeImage {
		return nil, nil, nil, nil
	}
	if msg.FileSize > maxIMAttachmentBytes {
		return nil, nil, nil, fmt.Errorf("attachment exceeds the %d MiB limit", maxIMAttachmentBytes>>20)
	}
	downloader, ok := adapter.(FileDownloader)
	if !ok {
		return nil, nil, nil, fmt.Errorf("platform %s does not support attachment download", msg.Platform)
	}
	attachmentCtx, cancel := context.WithTimeout(ctx, imAttachmentReadTimeout)
	defer cancel()
	reader, fileName, err := downloader.DownloadFile(attachmentCtx, msg)
	if err != nil {
		return nil, nil, nil, err
	}
	defer reader.Close()
	content, err := io.ReadAll(io.LimitReader(reader, maxIMAttachmentBytes+1))
	if err != nil {
		return nil, nil, nil, err
	}
	if len(content) > maxIMAttachmentBytes {
		return nil, nil, nil, fmt.Errorf("attachment exceeds the %d MiB limit", maxIMAttachmentBytes>>20)

View on GitHub (pinned to 988cbb0330)

Solutions

1. Ask the user to send a smaller file (under the MiB limit shown in the error)
2. Compress or convert the attachment before sending
3. Raise maxIMAttachmentBytes if your storage/document-parser backend can handle larger files

if msg.FileSize > maxIMAttachmentBytes {
    reply(ctx, "please send a file smaller than %d MiB", maxIMAttachmentBytes>>20)
    return
}

if err := s.prepareIMAttachments(ctx, msg, adapter); err != nil {
    if strings.Contains(err.Error(), "MiB limit") {
        // notify user their file is too large
    }
}

When it happens

Trigger: An IM message of type file or image whose FileSize metadata exceeds maxIMAttachmentBytes is processed by the IM service.

Common situations: Users uploading large videos/archives to a bot channel; platforms reporting FileSize in bytes inconsistently; lowering/raising the limit constant without communicating it to channel users.

Understand the failure class

Background: "File too large" / "file size exceeds limit" errors: why libraries cap file sizes and how to fix them — this error's family across 46 libraries.

Related errors

• a message can use at most %d attachments
• attachment has no file extension
• invite code has expired
• join request not found
• failed to retrieve: %s

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/38276e9a07e7e3dd. Report an issue: GitHub.