dart实现单client连接的grpc server (以ip地址作判断)
资料补充：
1、grpc在dart中的插件：https://pub.dev/packages/grpc
2、grpc的示例程序：https://github.com/grpc/grpc-dart/tree/master/example
如标题，假设现在已有grpc client/server程序。我这里的逻辑比较简单，基于ip地址的简单限制访问，但是允许来自一个ip地址的多次访问。
具体的实现逻辑在于，当接收到一个来自 client 的 grpc 接口访问，则优先获取client的ip信息：
如果和之前连接的IP地址相同或者之前还未有已连接的client，则允许连接并访问server；
否则，新的连接请求会收到 “Server is already handling another client” 错误；
当已连接的客户端断开连接时，连接计数会正确减少，允许新的client连接。
step1、导入需要的插件 .dart。
synchronized: ^3.1.0import 'dart:async';
import 'dart:io';
import 'package:grpc/grpc.dart';
import 'package:synchronized/synchronized.dart';
step2、增加一个连接管理的类。
// 添加连接计数器和锁
int _activeConnections = 0;
String? _currentClientIP; // 记录当前连接的客户端IP
final _connectionLock = Lock();// 创建连接管理器
class ConnectionManager {static String _getClientIP(ServiceCall call) {try {// 尝试从客户端元数据中获取IPif (call.clientMetadata != null) {// 检查X-Forwarded-For头（用于代理场景）final forwardedFor = call.clientMetadata!['x-forwarded-for'];if (forwardedFor != null && forwardedFor.isNotEmpty) {return forwardedFor;}// 检查X-Real-IP头（某些代理服务器使用）final realIP = call.clientMetadata!['x-real-ip'];if (realIP != null && realIP.isNotEmpty) {return realIP;}}// 尝试从远程地址获取IP（直接连接场景）if (call.remoteAddress != null) {return call.remoteAddress.toString();}} catch (e) {print('Error getting client IP: $e');}return 'Unknown IP';}static Future<void> checkConnection(ServiceCall call) async {bool canConnect = false;String clientIP = _getClientIP(call);await _connectionLock.synchronized(() {if (_activeConnections == 0) {// 没有活动连接，允许新连接_activeConnections++;_currentClientIP = clientIP;canConnect = true;print('New client connected from IP: $clientIP. Active connections: $_activeConnections');} else if (clientIP == _currentClientIP) {// 相同IP的客户端，允许连接_activeConnections++;canConnect = true;print('Additional connection from same IP: $clientIP. Active connections: $_activeConnections');} else {// 不同IP的客户端，拒绝连接print('Connection rejected for client IP: $clientIP - server is handling client from IP: $_currentClientIP');}});if (!canConnect) {throw GrpcError.unavailable('Server is already handling another client from different IP');}}static Future<void> releaseConnection(ServiceCall call) async {String clientIP = _getClientIP(call);await _connectionLock.synchronized(() {if (_activeConnections > 0) {_activeConnections--;print('Client disconnected from IP: $clientIP. Active connections: $_activeConnections');// 如果没有活动连接了，清除当前客户端IPif (_activeConnections == 0) {_currentClientIP = null;print('All connections closed, ready for new clients');}}});}
}
step3、在client发送grpc请求后，server端在服务类的实际操作函类前后加上连接管理类的判断，以及不符后的连接清除处理。
// 给XXXService添加连接限制
class ConnectionLimitedXXXService extends XXXServiceBase {Future<StringReply> usrFunCallReq(ServiceCall call, StringRequest request) async {await ConnectionManager.checkConnection(call); // 增加连接判断处理try {// procedurereturn StringReply()..message = jsonEncode(xxx);} finally {await ConnectionManager.releaseConnection(call); // 增加连接清除处理}}...
}