benbjohnson/litestream · error

failed to format response: %w

Error message

failed to format response: %w

What it means

When --json output is requested, Run re-marshals the successfully parsed InfoResponse with json.MarshalIndent for pretty printing. Failing here is effectively an internal invariant violation — a struct that json.Unmarshal just produced should serialize — but the error is wrapped and returned rather than ignored.

Source

Thrown at cmd/litestream/info.go:75

	}

	if resp.StatusCode != http.StatusOK {
		var errResp litestream.ErrorResponse
		if err := json.Unmarshal(body, &errResp); err == nil && errResp.Error != "" {
			return fmt.Errorf("info failed: %s", errResp.Error)
		}
		return fmt.Errorf("info failed: %s", string(body))
	}

	var result litestream.InfoResponse
	if err := json.Unmarshal(body, &result); err != nil {
		return fmt.Errorf("failed to parse response: %w", err)
	}

	if *jsonOutput {
		output, err := json.MarshalIndent(result, "", "  ")
		if err != nil {
			return fmt.Errorf("failed to format response: %w", err)
		}
		fmt.Println(string(output))
	} else {
		uptime := time.Duration(result.UptimeSeconds) * time.Second
		fmt.Printf("Litestream %s\n", result.Version)
		fmt.Printf("  PID:        %d\n", result.PID)
		fmt.Printf("  Uptime:     %s\n", uptime)
		fmt.Printf("  Started at: %s\n", result.StartedAt.Format(time.RFC3339))
		fmt.Printf("  Databases:  %d\n", result.DatabaseCount)
	}

	return nil
}

// Usage prints the help text for the info command.
func (c *InfoCommand) Usage() {
	fmt.Println(`
usage: litestream info [OPTIONS]

View on GitHub (pinned to 4ed7a308f6)

Solutions

1. Retry the command; if it persists, it indicates a build defect.
2. Verify you are running an official litestream release binary (rebuild from a clean checkout if custom).
3. Report the issue with your version string if it reproduces on an official release.
4. As a workaround use non-JSON output (omit --json) which prints via fmt.Printf and avoids the marshal path.

Example fix

// before
$ litestream info --json   # custom build with broken marshaler
// after
$ go install github.com/benbjohnson/litestream/cmd/litestream@latest
$ litestream info --json

if err := runInfoJSON(ctx); err != nil && strings.Contains(err.Error(), "failed to format response") {
    // marshal of a freshly-decoded struct should never fail; fall back to text output
    return runInfoText(ctx)
}

When it happens

Trigger: Theoretically triggered by a field in InfoResponse that cannot be marshaled (e.g. an unsupported value injected during decode such as a channel/func via custom UnmarshalJSON, or NaN-like values in custom types).

Common situations: Practically never hit by end users; encountered only with patched/modified builds of litestream where InfoResponse gained a non-JSON-serializable field or a custom marshaler with a bug.

Understand the failure class

Background: "JSON serialization failed", "not JSON serializable", "Failed to serialize": why JSON marshaling errors happen and how to fix them — this error's family across 46 libraries.

Related errors

• failed to format response: %w
• failed to marshal request: %w
• failed to format response: %w
• failed to format response: %w
• failed to marshal request: %w

AI-assisted analysis of benbjohnson/litestream@4ed7a308f6 (2026-09-06). Data as JSON: /api/errors/30d2e02e82d74405. Report an issue: GitHub.