Express+MySQL POST请求添加产品成功但报ERR_HTTP_HEADERS_SENT错误

问题现象 #

• 向MySQL发送POST请求添加产品，数据成功入库，但触发错误：Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

错误栈信息 #

at new NodeError (node:internal/errors:387:5)
at ServerResponse.setHeader (node:_http_outgoing:603:11)
at ServerResponse.header (C:\Users\DELL\Desktop\Small project\node_modules\express\lib\response.js:794:10)
at ServerResponse.send (C:\Users\DELL\Desktop\Small project\node_modules\express\lib\response.js:174:12)
at Query. (C:\Users\DELL\Desktop\Small project\server.js:47:16)
at Query. (C:\Users\DELL\Desktop\Small project\node_modules\mysql\lib\Connection.js:526:10)
at Query._callback (C:\Users\DELL\Desktop\Small project\node_modules\mysql\lib\Connection.js:488:16)
at Query.Sequence.end (C:\Users\DELL\Desktop\Small project\node_modules\mysql\lib\protocol\sequences\Sequence.js:83:24)
at Query._handleFinalResultPacket (C:\Users\DELL\Desktop\Small project\node_modules\mysql\lib\protocol\sequences\Query.js:149:8)
at Query.OkPacket (C:\Users\DELL\Desktop\Small project\node_modules\mysql\lib\protocol\sequences\Query.js:74:10) {
code: 'ERR_HTTP_HEADERS_SENT'}

相关代码 #

app.post("/product", (req, res, next) => {
  let product = {
    product_title: "lool",
    product_price: 4444.12,
    product_type: "sneakers",
    product_brand: "lol",
  };
  let sql = `INSERT INTO products SET ?`;

  db.query(sql, product, (err, result) => {
    if (err) {
      throw err;
    }
    console.log(result);
    return res.send("Completed");
  });

  res.send("Added");
});

错误原因 #

Express规定每个HTTP请求只能发送一次响应头和响应体。你的代码里，db.query是异步操作，不会阻塞后续代码执行，所以res.send("Added")会先被调用，发送第一次响应；当数据库查询完成后，回调函数里又执行return res.send("Completed")，尝试第二次发送响应，这就触发了ERR_HTTP_HEADERS_SENT错误。

解决方案 #

移除db.query外部的res.send("Added")，确保只在数据库操作完成后发送一次响应。同时优化错误处理方式，避免直接抛出错误导致服务器崩溃：

app.post("/product", (req, res, next) => {
  let product = {
    product_title: "lool",
    product_price: 4444.12,
    product_type: "sneakers",
    product_brand: "lol",
  };
  let sql = `INSERT INTO products SET ?`;

  db.query(sql, product, (err, result) => {
    if (err) {
      return res.status(500).send(err.message);
    }
    console.log(result);
    res.send("Completed");
  });
});

内容的提问来源于stack exchange，提问作者user19347248