gofr-dev/gofr · error

%w: settings: %w

Error message

%w: settings: %w

What it means

This is errMarshaling wrapped around a json.Marshal failure of the settings map in CreateIndex. Go's encoding/json cannot serialize every Go value; when settings contains channels, funcs, complex numbers, or a MarshalJSON implementation that errors, CreateIndex fails before any request is sent to the cluster.

Source

Thrown at pkg/gofr/datasource/elasticsearch/elasticsearch.go:126

		return
	}

	c.logger.Logf("connected to Elasticsearch successfully at : %v", c.config.Addresses)
}

// CreateIndex creates an index in Elasticsearch with the specified settings.
func (c *Client) CreateIndex(ctx context.Context, index string, settings map[string]any) error {
	if strings.TrimSpace(index) == "" {
		return errEmptyIndex
	}

	start := time.Now()

	tracedCtx, span := c.addTrace(ctx, "create-index", []string{index}, "")

	body, err := json.Marshal(settings)
	if err != nil {
		return fmt.Errorf("%w: settings: %w", errMarshaling, err)
	}

	req := esapi.IndicesCreateRequest{
		Index: index,
		Body:  bytes.NewReader(body),
	}

	res, err := req.Do(tracedCtx, c.client)
	if err != nil {
		return fmt.Errorf("%w: creating index: %w", errOperation, err)
	}
	defer res.Body.Close()

	if res.IsError() {
		return fmt.Errorf("%w: %s", errResponse, res.String())
	}

	c.sendOperationStats(start, fmt.Sprintf("CREATE INDEX %s", index),

View on GitHub (pinned to 187eb24962)

Solutions

1. Validate the settings map contains only JSON-safe values before calling CreateIndex.
2. Test json.Marshal(settings) locally to reproduce the exact encoder error message.
3. Replace non-serializable values with JSON primitives (string, number, bool, nil, slice, map).
4. Fix any custom MarshalJSON implementations on values nested inside settings.

Example fix

// before
settings := map[string]any{"number_of_shards": 1, "callback": onUpdate}
err := client.CreateIndex(ctx, "orders", settings) // error marshaling data: settings: ...
// after
settings := map[string]any{"number_of_shards": 1}
err := client.CreateIndex(ctx, "orders", settings)

if _, err := json.Marshal(settings); err != nil {
    return fmt.Errorf("invalid index settings: %w", err)
}
err := client.CreateIndex(ctx, index, settings)

if err := client.CreateIndex(ctx, index, settings); err != nil {
    var msg string
    if errors.As(err, &target) || strings.Contains(err.Error(), "error marshaling data") {
        msg = "settings map is not JSON-serializable"
    }
    return fmt.Errorf("create index failed: %v: %w", msg, err)
}

When it happens

Trigger: Calling CreateIndex(ctx, index, settings) where the settings map contains a non-JSON-encodable value (func, chan, complex) or a custom json.Marshaler that returns an error.

Common situations: Developers hit this when building index settings programmatically (analyzers, mappings) and accidentally including non-serializable values, or when reusing structs with custom marshaling logic that has bugs.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• %w: %s
• %w: query: %w
• invalid elasticsearch response
• error encoding operation
• %w: creating index: %w

AI-assisted analysis of gofr-dev/gofr@187eb24962 (2026-09-01). Data as JSON: /api/errors/7c0a793139154977. Report an issue: GitHub.