# 如何解决LocalSocket创建报错

#### 问题现象

LocalSocket无法正常使用，常见问题：

1.  创建LocalSocket报错：2301111 Connection refused。
2.  创建LocalSocket/LocalSocketServer报错：2301002 No such file or directory。
3.  客户端发送数据，服务端没有监听到消息。

#### 背景知识

*   LocalSocket：基于本地套接字文件建立数据流读写，相比TCP Scoket更加安全，不能通过抓包监听传输的数据，适用于同应用内不同进程间大量数据通信。跨应用间进程通信可参考IPC与RPC通信开发指导实现。
*   SOCKET 错误码：错误码映射关系为2301000+内核错误码，Server映射关系为2303100+内核错误码。比如2301111就是2301000+内核错误码111，在LocalSocket发起连接时出现。

#### 问题定位

1.  报错2301111 Connection refused通常需要排查服务端是否可连接，在LocalSocket连接前需要创建并启动LocalSocketServer，并检查LocalAddress是否一致。
2.  报错2301002 No such file or directory。对于LocalSocketServer，通常是没有本地套接字文件路径的权限，无法自动创建此文件。对于LocalSocket，除检查路径外，需要保证已提前创建LocalSocketServer并调用其listen函数自动创建套接字文件。
3.  对于服务端无法监听到发送的消息，需要确保LocalSocket客户端在发送数据前，服务端已开启了on('connect')以及回调中连接的on('message')监听。否则服务端没有监听到客户端连接事件，就无法再监听到对应连接的其他事件。

#### 分析结论

1.  2301002 No such file or directory问题：应用没有权限访问LocalAddress的address，或客户端没有使用同一个套接字文件。
2.  2301111 Connection refused和服务端没有接收到客户端发送的消息问题：使用LocalSocket时没有先启动LocalSocketServer，再启动客户端。

#### 修改建议

1.  LocalAddress的address配置应用沙箱路径，并且客户端和服务端使用同一个套接字文件：
    
    ```
    genLocalAddress(socketFileName: string) {
      let context: common.UIAbilityContext = this.getUIContext().getHostContext() as common.UIAbilityContext;
      let sandboxPath: string = context.filesDir + '/' + socketFileName;
      let localAddress: socket.LocalAddress = {
        address: sandboxPath
      };
      return localAddress;
    }
    ```
    
2.  LocalSocket使用需要先启动LocalSocketServer：
    
    ```
    // 创建并绑定本地套接字文件，进行监听。
    this.server.listen(this.localAddress).then(() => {
      console.info('LocalSocket Server listen success');
    }).catch((err: BusinessError) => {
      console.error('LocalSocket Server listen fail: ' + JSON.stringify(err));
    });
    
    // 订阅LocalSocketServer的connect事件。
    this.server.on('connect', (connection: socket.LocalSocketConnection) => {
      console.info('LocalSocket Server 监听到客户端连接: ' + JSON.stringify(connection.clientId));
      // 订阅LocalSocketConnection相关的事件。
      connection.on('message', (value: socket.LocalSocketMessageInfo) => {
        console.info('LocalSocket Server total: ' + JSON.stringify(value));
        console.info('LocalSocket Server message information: ' + this.decodeMessage(value));
        // ...
      });
    
      connection.on('error', (err: BusinessError) => {
        console.error('LocalSocket Server err:' + JSON.stringify(err));
      });
    
      // 向客户端发送数据。
      this.sendMessage(connection, 'Hello Client!');
      // ...
    });
    ```
    
3.  再启动LocalSocket客户端发送消息：
    
    ```
    // 启动客户端端前，需要先启动LocalSocketServer，否则报错：2301111 Connection refused
    let connectOpt: socket.LocalConnectOptions = {
      address: this.localAddress,
      timeout: 6000
    };
    
    this.client.connect(connectOpt).then(() => {
      console.info('LocalSocket Client connect success');
    }).catch((err: BusinessError) => {
      console.error('LocalSocket Client connect fail: ' + JSON.stringify(err));
    });
    
    this.client.on('message', (value: socket.LocalSocketMessageInfo) => {
      console.info('LocalSocket Server total: ' + JSON.stringify(value));
      console.info('LocalSocket Server message information: ' + this.decodeMessage(value));
    });
    this.client.on('connect', () => {
      console.info('LocalSocket Client on connect');
    });
    this.client.on('close', () => {
      console.info('LocalSocket Client on close');
    });
    ```
    

完整示例如下：

```
import { socket } from '@kit.NetworkKit';
import { common } from '@kit.AbilityKit';
import { util } from '@kit.ArkTS';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct LocalSocketPage {
  private server: socket.LocalSocketServer = socket.constructLocalSocketServerInstance();
  private client: socket.LocalSocket = socket.constructLocalSocketInstance();
  private localAddress: socket.LocalAddress = this.genLocalAddress('socket_1'); // 创建本地文件，server和client均需对此路径具备访问权限

  genLocalAddress(socketFileName: string) {
    let context: common.UIAbilityContext = this.getUIContext().getHostContext() as common.UIAbilityContext;
    let sandboxPath: string = context.filesDir + '/' + socketFileName;
    let localAddress: socket.LocalAddress = {
      address: sandboxPath
    };
    return localAddress;
  }

  decodeMessage(data: socket.LocalSocketMessageInfo): string {
    if (data?.message) {
      let decoder = util.TextDecoder.create('utf-8');
      let message = decoder.decodeToString(new Uint8Array(data.message));
      return message;
    }
    return '';
  }

  sendMessage(socket: socket.LocalSocket | socket.LocalSocketConnection, message: string): void {
    let sendOpt: socket.LocalSendOptions = {
      data: message
    };
    socket.send(sendOpt).then(() => {
      console.info('LocalSocket send message success');
    }).catch((err: BusinessError) => {
      console.info('LocalSocket send message failed: ' + JSON.stringify(err));
    });
  }

  build() {
    Column({ space: 24 }) {
      Button('启动LocalSocket服务端')
        .onClick(() => {
          // 创建并绑定本地套接字文件，进行监听。
          this.server.listen(this.localAddress).then(() => {
            console.info('LocalSocket Server listen success');
          }).catch((err: BusinessError) => {
            console.error('LocalSocket Server listen fail: ' + JSON.stringify(err));
          });

          // 订阅LocalSocketServer的connect事件。
          this.server.on('connect', (connection: socket.LocalSocketConnection) => {
            console.info('LocalSocket Server 监听到客户端连接: ' + JSON.stringify(connection.clientId));
            // 订阅LocalSocketConnection相关的事件。
            connection.on('message', (value: socket.LocalSocketMessageInfo) => {
              console.info('LocalSocket Server total: ' + JSON.stringify(value));
              console.info('LocalSocket Server message information: ' + this.decodeMessage(value));
              // ...
            });

            connection.on('error', (err: BusinessError) => {
              console.error('LocalSocket Server err:' + JSON.stringify(err));
            });

            // 向客户端发送数据。
            this.sendMessage(connection, 'Hello Client!');
            // ...
          });
        });
      Button('启动LocalSocket客户端').onClick(() => {
        // 启动客户端端前，需要先启动LocalSocketServer，否则报错：2301111 Connection refused
        let connectOpt: socket.LocalConnectOptions = {
          address: this.localAddress,
          timeout: 6000
        };

        this.client.connect(connectOpt).then(() => {
          console.info('LocalSocket Client connect success');
        }).catch((err: BusinessError) => {
          console.error('LocalSocket Client connect fail: ' + JSON.stringify(err));
        });

        this.client.on('message', (value: socket.LocalSocketMessageInfo) => {
          console.info('LocalSocket Server total: ' + JSON.stringify(value));
          console.info('LocalSocket Server message information: ' + this.decodeMessage(value));
        });
        this.client.on('connect', () => {
          console.info('LocalSocket Client on connect');
        });
        this.client.on('close', () => {
          console.info('LocalSocket Client on close');
        });
      });
      Button('客户端发送数据').onClick(() => {
        // 需要服务端先使用on('connect')、on('message')监听到客户端连接，否则无法监听到消息
        this.sendMessage(this.client, 'Hello Server!');
      });
    }
    .height('100%')
    .width('100%');
  }
}
```