Golang uses regularity to match substring functions

const SERVICE_IMPL_RULE = ".*?\\.NewServer\\(new\\((.*?)\\)\\)"

// getServiceImpl  return : CompassInsightServiceImpl
//{
    { .ServiceImpl }} = CompassInsightServiceImpl
// svr := insight_service.NewServer(new(CompassInsightServiceImpl))
func getServiceImpl(filePath string) string {
    f, err := os.Open(filePath)
    if err != nil {
        return ""
    }
    buf := bufio.NewReader(f)
    for {
        line, err := buf.ReadString('\n')

        line = strings.TrimSpace(line)
        if strings.Contains(line, ".NewServer(new(") {
            byRegex, err := GetOneStringByRegex(line, SERVICE_IMPL_RULE)
            if err != nil {
                log.Error(err)
                return ""
            }
            return byRegex
        }

        if err != nil {
            if err == io.EOF {
                return ""
            }
            return ""
        }
    }

}

const SVR_RULE = "svr := (.*?)\\.NewServer\\(new\\(.*?\\)\\)"

// getNewServerCodeLine  return : insight_service
// originLine =   svr := insight_service.NewServer(new(CompassInsightServiceImpl))
//{
    { .NewServerCodeLine }} = insight_service
//svr := {
    { .NewServerCodeLine }}.NewServer({
    { .ServiceImpl }}, server.WithMiddleware(transform.ServerTransform), server.WithMiddleware(logmv.ServerLog))
//svr := insight_service.NewServer( CompassInsightServiceImpl, server.WithMiddleware(transform.ServerTransform), server.WithMiddleware(logmv.ServerLog))
func getNewServerCodeLine(filePath string) string {
    f, err := os.Open(filePath)
    if err != nil {
        return ""
    }
    buf := bufio.NewReader(f)
    for {
        line, err := buf.ReadString('\n')

        line = strings.TrimSpace(line)
        if strings.Contains(line, ".NewServer(new(") {
            byRegex, err := GetOneStringByRegex(line, SVR_RULE)
            if err != nil {
                log.Error(err)
                return ""
            }
            return byRegex
        }

        if err != nil {
            if err == io.EOF {
                return ""
            }
            return ""
        }
    }
}

// GetOneStringByRegex  Use regular to match substring functions ：
// Use cases ：
// from  img[/static/upload/xxxx/xxx.jpg]  In order to get  xxxx/xxx.jpg
//url, _ = GetOneStringByRegex(str, "img\\[.*?/static/upload/(.*?)\\]")
func GetOneStringByRegex(str, rule string) (string, error) {
    reg, err := regexp.Compile(rule)
    if reg == nil || err != nil {
        return "", errors.New(" Regular Compile error :" + err.Error())
    }
    // Extract key information 
    result := reg.FindStringSubmatch(str)
    if len(result) < 1 {
        return "", errors.New(" No substring was obtained ")
    }
    return result[1], nil
}