Exception Filters

Exception filters catch errors thrown during request processing and produce HTTP responses. GoNest has a built-in DefaultExceptionFilter that handles *HTTPException errors.

Default Error Response

When a handler returns an *HTTPException, the default filter produces:

{
  "statusCode": 404,
  "message": "cat not found",
  "timestamp": "2024-01-15T10:30:00Z",
  "path": "/cats/999"
}

Throwing Errors

func (c *CatsController) findOne(ctx gonest.Context) error {
    cat := c.service.FindByID(id)
    if cat == nil {
        return gonest.NewNotFoundException("cat not found")
    }
    return ctx.JSON(200, cat)
}

All built-in exceptions:

Function	Status
`NewBadRequestException(msg)`	400
`NewUnauthorizedException(msg)`	401
`NewForbiddenException(msg)`	403
`NewNotFoundException(msg)`	404
`NewConflictException(msg)`	409
`NewUnprocessableEntityException(msg)`	422
`NewTooManyRequestsException(msg)`	429
`NewInternalServerError(msg)`	500

Custom Exception Filter

type CustomFilter struct{}

func (f *CustomFilter) Catch(err error, host gonest.ArgumentsHost) error {
    httpCtx := host.SwitchToHTTP()
    resp := httpCtx.Response()

    code := 500
    msg := err.Error()
    if httpErr, ok := err.(*gonest.HTTPException); ok {
        code = httpErr.StatusCode()
    }

    return resp.Status(code).JSON(map[string]any{
        "error":   true,
        "code":    code,
        "message": msg,
    })
}

// Register globally
app.UseGlobalFilters(&CustomFilter{})

Filter Priority

Route-level filters run first, then controller-level, then global, then the built-in default.