microsoft/typescript-go · error · ErrorCode

-32602

-32602

Error message

%w: expected no params, got %s

What it means

Returned by lsproto.UnmarshalParams when a method whose params type is the marker NoParams (declared to take no parameters, e.g. shutdown or the workspace/*/refresh requests) arrives with a non-empty params payload. The base protocol lets params be optional, so this library enforces the declaration at dispatch time and wraps the error with ErrorCodeInvalidParams (-32602) so it maps to a standard JSON-RPC error response.

Source

Thrown at internal/lsp/lsproto/lsp.go:250

//
// A [NoParams] method must be given no params; every other method must be given
// params as an object or array. A violation returns [ErrorCodeInvalidParams].
func UnmarshalParams[T any](req *RequestMessage) (T, error) {
	var params T
	var raw json.Value
	if req.Params != nil {
		v, ok := req.Params.(json.Value)
		if !ok {
			return params, fmt.Errorf("%w: unexpected params type %T", ErrorCodeInvalidParams, req.Params)
		}
		raw = v
	}

	// params is the zero value of T; this asserts on its type, i.e. whether the
	// method was declared with NoParams.
	if _, declaresNoParams := any(params).(NoParams); declaresNoParams {
		if len(raw) != 0 {
			return params, fmt.Errorf("%w: expected no params, got %s", ErrorCodeInvalidParams, raw)
		}
		return params, nil
	}

	// The base protocol defines params as `array | object`; reject anything else
	// (absent, null, or a scalar).
	if k := raw.Kind(); k != '{' && k != '[' {
		return params, fmt.Errorf("%w: params must be an object or array", ErrorCodeInvalidParams)
	}
	if err := json.Unmarshal(raw, &params); err != nil {
		return params, fmt.Errorf("%w: %w", ErrorCodeInvalidParams, err)
	}
	return params, nil
}

type Null struct{}

func (Null) UnmarshalJSONFrom(dec *json.Decoder) error {

View on GitHub (pinned to 1bcfa18d79)

Solutions

  1. Omit the params member entirely from the JSON-RPC message for methods declared NoParams.
  2. If your client framework cannot omit params, special-case empty objects to drop the key before sending.
  3. When writing server handlers, only dispatch methods via UnmarshalParams[lsproto.NoParams] when the spec truly has no params; otherwise accept the empty object shape your client emits.

Example fix

// before
{"jsonrpc":"2.0","id":1,"method":"shutdown","params":{}}
// after
{"jsonrpc":"2.0","id":1,"method":"shutdown"}
Defensive patterns

Strategy: validation

Validate before calling

// drop params entirely for parameterless methods before writing the frame
var noParamsMethods = map[string]bool{
    "shutdown": true,
    "workspace/semanticTokens/refresh": true,
    "workspace/inlayHint/refresh": true,
    "workspace/codeLens/refresh": true,
    "workspace/diagnostic/refresh": true,
    "exit": true,
}

func frame(method string, params any) map[string]any {
    m := map[string]any{"jsonrpc": "2.0", "method": method}
    if !noParamsMethods[method] {
        m["params"] = params
    }
    return m
}

Type guard

func isNoParamsMethod(method string) bool {
    switch method {
    case "shutdown", "exit", "workspace/semanticTokens/refresh", "workspace/inlayHint/refresh", "workspace/codeLens/refresh", "workspace/diagnostic/refresh":
        return true
    }
    return false
}

Try / catch

// server-side dispatcher: map -32602 'expected no params' to a clean response
if errors.Is(err, lsproto.ErrorCodeInvalidParams) && strings.Contains(err.Error(), "expected no params") {
    return sendError(id, fmt.Errorf("%w: method takes no parameters", lsproto.ErrorCodeInvalidParams))
}

Prevention

When it happens

Trigger: A client sends "params": {} or any params value with the shutdown request, or attaches params to a notification whose Go handler dispatches via UnmarshalParams[lsproto.NoParams]. Line 248-251 checks the type assertion any(params).(NoParams) and rejects any raw bytes with len != 0.

Common situations: Client frameworks that always inject an empty params object into every request; test harnesses templating requests with a fixed params key; middleware that rewrites absent params to {} or null; protocol libraries that cannot express parameterless methods.

Related errors

AI-assisted analysis of microsoft/typescript-go@1bcfa18d79 (2026-08-16). Data as JSON: /api/errors/395b8249d77fb60e. Report an issue: GitHub.