Node.js SOAP服务器：如何从Promise异步操作返回正确数据？

问题场景 #

基于Node.js搭建的SOAP服务器，调用异步Promise函数操作Oracle数据库，尝试用XMLWriter构建包含查询结果的XML响应，但客户端仅收到空的<result/>元素，无法获取数据库查询添加的子元素。核心代码如下：

const soap = require('soap');
const http = require('http');
const XMLWriter = require('xml-writer');

const service = {
   ImpDispatcherService: {
      ImpDispatcher: {
         performTest: function (args) {
            const xw = new XMLWriter(true);
            xw.startDocument();
            xw.startElement('result');
            queryDatabase(args.parameter1, xw).then(success => {
               console.log(success);
               xw.endDocument();
               console.log(xw.toString()); // -> prints the full XML-File
            });             
            return { testResult: xw.toString() };
         }
      }
   }
};

var server = http.createServer((request, response) => {
   response.end('404: Not Found: ' + request.url);
});

// Create the SOAP server
const xml = require('fs').readFileSync(`${__dirname}/ImpDispatcherService.wsdl`, 'utf8');
var server = http.createServer((request, response) => {
   response.end('404: Not Found: ' + request.url);
});

server.listen(8000, 'localhost');
soap.listen(server, '/imp', service, xml, () => {
   logger.info('Server initialized');
});

async function queryDatabase(pars) {
   const oracledb = require('oracledb');
   const connection = await oracledb.getConnection(db);
   const result = await connection.execute(`BEGIN :ret := getResult(${pars}); END;`, {ret: { dir: oracledb.BIND_OUT, type: oracledb.CURSOR } });
   let row;
   while (row = await result.outBinds.ret.getRow()) {
      xw.writeElement('tag', row.blabla);
   }

   return true;
}

问题原因 #

performTest方法调用queryDatabase后直接返回xw.toString()，此时异步数据库查询尚未完成，XMLWriter还未添加任何子元素，因此返回的是仅包含空<result/>标签的XML字符串。

解决方案 #

将performTest改为异步函数，等待queryDatabase执行完成后再构建并返回响应数据，同时修正queryDatabase的参数传递问题：

修改后的核心代码 #

const service = {
   ImpDispatcherService: {
      ImpDispatcher: {
         // 改为async函数，支持await异步操作
         performTest: async function (args) {
            const xw = new XMLWriter(true);
            xw.startDocument();
            xw.startElement('result');
            // 等待数据库查询完成再继续
            await queryDatabase(args.parameter1, xw);
            xw.endDocument();
            return { testResult: xw.toString() };
         }
      }
   }
};

// 修正queryDatabase，接收xw参数并完成数据库操作
async function queryDatabase(pars, xw) {
   let connection;
   try {
      const oracledb = require('oracledb');
      connection = await oracledb.getConnection(db);
      const result = await connection.execute(`BEGIN :ret := getResult(${pars}); END;`, {ret: { dir: oracledb.BIND_OUT, type: oracledb.CURSOR } });
      let row;
      while (row = await result.outBinds.ret.getRow()) {
         xw.writeElement('tag', row.blabla);
      }
      // 关闭数据库游标
      await result.outBinds.ret.close();
   } finally {
      // 确保数据库连接关闭，避免资源泄漏
      if (connection) {
         await connection.close();
      }
   }
   return true;
}

关键修改点 #

• 将performTest声明为async函数，使用await等待queryDatabase执行完毕，保证XMLWriter完成所有子元素写入后再返回结果。
• 为queryDatabase补充xw参数，确保能正确向XMLWriter添加数据库查询到的子元素。
• 添加try/finally块，确保数据库连接和游标在操作完成后关闭，避免资源泄漏。
• 移除原代码中重复定义的http.createServer实例。

完整修改后代码 #

const soap = require('soap');
const http = require('http');
const XMLWriter = require('xml-writer');
const oracledb = require('oracledb');

// 数据库配置，需根据实际情况填写
const db = {
  user: 'your_db_user',
  password: 'your_db_password',
  connectString: 'your_db_connect_string'
};

const service = {
   ImpDispatcherService: {
      ImpDispatcher: {
         performTest: async function (args) {
            const xw = new XMLWriter(true);
            xw.startDocument();
            xw.startElement('result');
            await queryDatabase(args.parameter1, xw);
            xw.endDocument();
            return { testResult: xw.toString() };
         }
      }
   }
};

// 创建HTTP服务器
const server = http.createServer((request, response) => {
   response.end('404: Not Found: ' + request.url);
});

// 读取WSDL文件
const xml = require('fs').readFileSync(`${__dirname}/ImpDispatcherService.wsdl`, 'utf8');

// 启动服务器并监听SOAP请求
server.listen(8000, 'localhost');
soap.listen(server, '/imp', service, xml, () => {
   console.info('Server initialized');
});

async function queryDatabase(pars, xw) {
   let connection;
   try {
      connection = await oracledb.getConnection(db);
      const result = await connection.execute(`BEGIN :ret := getResult(${pars}); END;`, {ret: { dir: oracledb.BIND_OUT, type: oracledb.CURSOR } });
      let row;
      while (row = await result.outBinds.ret.getRow()) {
         xw.writeElement('tag', row.blabla);
      }
      await result.outBinds.ret.close();
   } catch (err) {
      console.error('Database query error:', err);
      throw err; // 抛出错误让SOAP框架处理异常响应
   } finally {
      if (connection) {
         await connection.close();
      }
   }
   return true;
}

内容的提问来源于stack exchange，提问作者Wernfried Domscheit