What causes "expected JSON object: %w" in alibaba/open-code-review?

Pass a flat JSON object of strings: '{"Authorization":"Bearer t"}'

expected JSON object: %w

Error message

expected JSON object: %w

What it means

parseMCPHeaders wraps the json.Unmarshal failure with "expected JSON object: <cause>" when the headers value cannot be decoded into map[string]string. The headers field must be a flat JSON object whose keys and values are strings; arrays, bare strings, or nested objects fail here, and the error is then surfaced by setMCPServerValue as "invalid headers for ...".

Source

Thrown at cmd/opencodereview/config_cmd.go:939

			filtered = append(filtered, t)
		}
		entry.Tools = filtered
	case "setup":
		entry.Setup = value
	default:
		return fmt.Errorf("unknown MCP server field %q: supported fields are type, command, args, env, url, headers, tools, setup", field)
	}

	cfg.MCPServers[name] = entry
	return nil
}

// parseMCPHeaders parses a JSON object of header key-value pairs.
// Example: {"Authorization": "Bearer $TOKEN", "X-Custom": "value"}
func parseMCPHeaders(value string) (map[string]string, error) {
	var m map[string]string
	if err := json.Unmarshal([]byte(value), &m); err != nil {
		return nil, fmt.Errorf("expected JSON object: %w", err)
	}
	for k, v := range m {
		if k == "" {
			return nil, fmt.Errorf("header name must not be empty")
		}
		if v == "" {
			return nil, fmt.Errorf("header value for %q must not be empty", k)
		}
	}
	return m, nil
}

func (c *Config) ensureTelemetry() {
	if c.Telemetry == nil {
		c.Telemetry = &TelemetryConfig{}
	}
}

View on GitHub (pinned to 5cf97d0d15)

Solutions

Pass a flat JSON object of strings: '{"Authorization":"Bearer t"}'
Quote all JSON keys and ensure values are strings (use "123" not 123)
Read the wrapped json error after `expected JSON object:` for the exact offset

Example fix

// before
ocr config set mcp-servers.myserver.headers '{"X-Retries": 3}'
// after
ocr config set mcp-servers.myserver.headers '{"X-Retries": "3"}'

Defensive patterns

Strategy: validation

Validate before calling

func validHeaderObject(s string) bool {
    var m map[string]string
    return json.Unmarshal([]byte(s), &m) == nil
}

Type guard

func asHeaderMap(v any) (map[string]string, bool) { m, ok := v.(map[string]string); return m, ok }

Try / catch

_, err := parseMCPHeaders(raw)
if err != nil {
    var se *json.SyntaxError
    if errors.As(err, &se) { fmt.Fprintf(os.Stderr, "bad JSON at offset %d", se.Offset) }
    return err
}

Prevention

Ensure all JSON keys are quoted and values are strings
Pipe the candidate value through `jq type` to confirm it is an object
Avoid nested header values — flatten to strings first

When it happens

Trigger: `ocr config set mcp-servers.myserver.headers '["a"]'` (array), `'{"a": 123}'` (non-string value), or a bare unquoted word; also malformed JSON like a missing brace or unquoted key.

Common situations: Non-string header values (numbers/booleans) in the JSON; single quotes inside the JSON unquoted by the shell; forgetting the braces around key-value pairs.

Related errors

AI-assisted analysis of alibaba/open-code-review@5cf97d0d15 (2026-09-02). Data as JSON: /api/errors/f31e62828f83c362. Report an issue: GitHub.