SQL连接器配置错误引发MySQL连接失败，寻求故障原因

我运行以下Ballerina代码：

import ballerina/http;
import ballerina/sql;
import ballerinax/mysql;
import ballerinax/mysql.driver as _;

type isValid record {
    boolean valid;
    string nic;
};

type Person record {
    string mic;
    @sql:Column {name: "firstname"}
    string firstName;
    @sql:Column {
        name: "lastname"
    }
    string lastName;
};

configurable string database = ?;
configurable string username = ?;
configurable string host = ?;

mysql:Client mysqlEp = check new (host = host, user = username, database = database);

service / on new http:Listener(9090) {
    resource function get checkNic/[string nic]() returns isValid|error? {

        Person|error person = check mysqlEp->queryRow(`select * from nic_details where nic=${nic.trim()}`);

        if (person is error) {
            isValid result = {
                valid: false,
                nic: nic
            };
            return result;
        } else {
            isValid result = {
                valid: true,
                nic: nic
            };
            return result;
        }
    }

    resource function get path() {

    }
}

出现如下错误：

error: Error in SQL connector configuration: Failed to initialize pool: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. Caused by :Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. Caused by :Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. Caused by :Connection refused

已确认使用默认端口3306，XAMPP显示MySQL服务器正运行于该端口，主机设置为localhost，以下是错误的可能原因及排查方向：

可能原因 #

• IPv6解析冲突：部分系统中localhost会优先解析为IPv6地址::1，但XAMPP的MySQL可能仅绑定了IPv4的127.0.0.1，导致连接被拒。尝试将host配置改为127.0.0.1强制使用IPv4连接。
• 防火墙/安全软件拦截：本地防火墙、杀毒软件可能阻断了Ballerina进程访问3306端口。临时关闭防火墙或添加Ballerina进程的访问权限，测试是否能正常连接。
• MySQL用户权限不足：当前配置的数据库用户可能没有从localhost或127.0.0.1连接的权限。登录MySQL执行SELECT user, host FROM mysql.user;，查看对应用户的host字段是否为localhost或%；若不是，执行GRANT ALL PRIVILEGES ON 你的数据库名.* TO '你的用户名'@'localhost';并执行FLUSH PRIVILEGES;刷新权限。
• 连接器与MySQL版本不兼容：使用的ballerinax/mysql连接器版本可能与XAMPP中的MySQL版本不匹配。检查连接器版本，尝试升级或降级到兼容的版本。
• 端口实际被占用或配置不符：虽然XAMPP显示运行在3306，但可能存在其他进程占用该端口，或MySQL配置文件（my.cnf/my.ini）中修改了端口。执行netstat -ano | findstr :3306（Windows）或lsof -i :3306（Linux/macOS），确认端口占用情况及实际监听端口。
• 连接参数缺失：代码中创建mysql:Client时未显式指定端口，虽然默认是3306，但可以尝试添加port = 3306参数，确保连接配置完全匹配。

内容的提问来源于stack exchange，提问作者Gabil