SigNoz/signoz · error · model.ApiError

couldn't JSON decode existingFilter: %w

Error message

couldn't JSON decode existingFilter: %w

What it means

After successfully base64-decoding 'existingFilter', the bytes must be valid JSON matching v3.FilterSet. This error means decoding succeeded but json.Unmarshal failed.

Source

Thrown at pkg/query-service/app/parser.go:570

		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
}

func parseFilterAttributeKeyRequest(r *http.Request) (*v3.FilterAttributeKeyRequest, error) {
	var req v3.FilterAttributeKeyRequest

	dataSource := v3.DataSource(r.URL.Query().Get("dataSource"))

View on GitHub (pinned to 5069bf80b0)

Solutions

1. Validate the JSON locally against the FilterSet schema (operator string, items array of filter items) before encoding
2. Print the decoded bytes and run them through a JSON validator
3. Ensure you encoded the final JSON once, not twice

Example fix

// before
enc := base64.RawURLEncoding.EncodeToString([]byte(`{"items": "foo"}`))
// after
enc := base64.RawURLEncoding.EncodeToString([]byte(`{"operator":"AND","items":[]}`))

decoded, _ := base64.RawURLEncoding.DecodeString(b64)
var fs v3.FilterSet
if err := json.Unmarshal(decoded, &fs); err != nil { return fmt.Errorf("existingFilter is not valid FilterSet JSON") }

func isValidFilterSetJSON(b []byte) bool { var fs v3.FilterSet; return json.Unmarshal(b, &fs) == nil }

Catch the 400 response, decode the message, and surface which stage (base64 vs JSON) failed to the user for correction.

When it happens

Trigger: existingFilter decodes to non-JSON bytes, or JSON with wrong types (e.g. items as a string instead of array, operator misspelled structure).

Common situations: Encoding a partial/mocked object; schema drift between the client's FilterSet shape and the server's v3.FilterSet; double-encoding so the outer decode yields base64 text.

Related errors

• invalid request body: %v
• error decoding request: %v
• couldn't base64 decode existingFilter: %w
• cannot parse the request body: %v
• CodeLicenseUnavailable

AI-assisted analysis of SigNoz/signoz@5069bf80b0 (2026-08-28). Data as JSON: /api/errors/b8d8503529989f8e. Report an issue: GitHub.