SigNoz/signoz · error · model.ApiError

couldn't base64 decode existingFilter: %w

Error message

couldn't base64 decode existingFilter: %w

What it means

parseQBFilterSuggestionsRequest accepts an optional 'existingFilter' query param that must be base64 (RawURL encoding) of a JSON FilterSet. This error means the base64 decode step itself failed.

Source

Thrown at pkg/query-service/app/parser.go:564

	if err != nil {
		return nil, err
	}

	examplesLimit, err := parsePositiveIntQP(
		"examplesLimit",
		baseconstants.DefaultFilterSuggestionsExamplesLimit,
		baseconstants.MaxFilterSuggestionsExamplesLimit,
	)
	if err != nil {
		return nil, err
	}

	var existingFilter *v3.FilterSet
	existingFilterB64 := r.URL.Query().Get("existingFilter")
	if len(existingFilterB64) > 0 {
		decodedFilterJson, err := base64.RawURLEncoding.DecodeString(existingFilterB64)
		if err != nil {
			return nil, model.BadRequest(fmt.Errorf("couldn't base64 decode existingFilter: %w", err))
		}

		existingFilter = &v3.FilterSet{}
		err = json.Unmarshal(decodedFilterJson, existingFilter)
		if err != nil {
			return nil, model.BadRequest(fmt.Errorf("couldn't JSON decode existingFilter: %w", err))
		}
	}

	searchText := r.URL.Query().Get("searchText")

	return &v3.QBFilterSuggestionsRequest{
		DataSource:      dataSource,
		SearchText:      searchText,
		ExistingFilter:  existingFilter,
		AttributesLimit: attributesLimit,
		ExamplesLimit:   examplesLimit,
	}, nil

View on GitHub (pinned to 5069bf80b0)

Solutions

1. Encode with base64.RawURLEncoding (URL-safe, no padding) in Go, or base64url without padding elsewhere
2. Verify the value wasn't truncated or re-encoded by a proxy
3. If passing literal JSON, remove the param and send via body if the API version supports it

Example fix

// before
?existingFilter={"operator":"AND","items":[]}
// after (Go)
enc := base64.RawURLEncoding.EncodeToString([]byte(filterJSON))
// use ?existingFilter=<enc>

if _, err := base64.RawURLEncoding.DecodeString(existingFilterB64); err != nil { return fmt.Errorf("existingFilter must be base64url without padding") }

func isRawURLBase64(s string) bool { _, err := base64.RawURLEncoding.DecodeString(s); return err == nil }

When it happens

Trigger: Calling the query-builder suggestions endpoint with existingFilter set to a raw JSON string, standard base64 with padding, or corrupted/truncated base64.

Common situations: Sending JSON directly without encoding; using base64.StdEncoding with +/= characters instead of URL-safe no-padding encoding; string truncation from URL length limits.

Related errors

• couldn't JSON decode existingFilter: %w
• CodeLicenseUnavailable
• CodeInvalidInput
• CodeForbidden
• CodeNotFound

AI-assisted analysis of SigNoz/signoz@5069bf80b0 (2026-08-28). Data as JSON: /api/errors/8eef0d9fe1c59048. Report an issue: GitHub.