Node.js 错误[ERR_HTTP_HEADERS_SENT]：在使用Firebase将头发送到客户端节点后，无法设置头

说明
每次我包括

response.send（snapshot.val（））发生此错误，NodeJS服务器崩溃。我正在使用Postman测试带有标头的API端点，它工作正常。


输出

On terminal 401 Unauthorized 

[2020-11-05T13:23:24.421Z]  @firebase/database: FIREBASE WARNING: Exception was thrown by user callback. Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

const getsRoute = require('./routes/gets');
app.use('/api/v1', getsRoute);

//on other file
const auth = require('../middleware/auth');
router.get('/products', auth, (req, res) => {
    initialPage.getBusinesses(res);
});

const initialPage = {
    getBusinesses(response) {
        ref.orderByKey()
        .limitToLast(20)
        .on('value', function(snapshot){
            response.json(snapshot.val()); 
            return snapshot.val();
        })
    }
}

  searchApi = async() => {
        const response = await axios.get('http://33c75838823c90.ngrok.io/api/v1/products',{
                headers: {
                    "Content-Type": "application/json",
                    "Accept": "application/json",
                    "x-auth-token":"jgiiHDgfdeizI1NiIJ9.eyJfaWQiOiI1ZmEwMWMzZmM4YjIwYjBjZDQyMmJkNzUiLCJpYXQiOjE2MDQ0MTAwMDZ0KwFAgVtsJUQw"
                }
            }
        ).catch((error) => {
            console.log("ERROR FROM AXIOS:", error)
          });
        console.log("RESPONSE DATA: %%%%%%%", response.data)
        this.setState({results: [response.data]});
       
    }

NodeJS

On terminal 401 Unauthorized 

[2020-11-05T13:23:24.421Z]  @firebase/database: FIREBASE WARNING: Exception was thrown by user callback. Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

const getsRoute = require('./routes/gets');
app.use('/api/v1', getsRoute);

//on other file
const auth = require('../middleware/auth');
router.get('/products', auth, (req, res) => {
    initialPage.getBusinesses(res);
});

const initialPage = {
    getBusinesses(response) {
        ref.orderByKey()
        .limitToLast(20)
        .on('value', function(snapshot){
            response.json(snapshot.val()); 
            return snapshot.val();
        })
    }
}

  searchApi = async() => {
        const response = await axios.get('http://33c75838823c90.ngrok.io/api/v1/products',{
                headers: {
                    "Content-Type": "application/json",
                    "Accept": "application/json",
                    "x-auth-token":"jgiiHDgfdeizI1NiIJ9.eyJfaWQiOiI1ZmEwMWMzZmM4YjIwYjBjZDQyMmJkNzUiLCJpYXQiOjE2MDQ0MTAwMDZ0KwFAgVtsJUQw"
                }
            }
        ).catch((error) => {
            console.log("ERROR FROM AXIOS:", error)
          });
        console.log("RESPONSE DATA: %%%%%%%", response.data)
        this.setState({results: [response.data]});
       
    }

产生错误的代码

On terminal 401 Unauthorized 

[2020-11-05T13:23:24.421Z]  @firebase/database: FIREBASE WARNING: Exception was thrown by user callback. Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

const getsRoute = require('./routes/gets');
app.use('/api/v1', getsRoute);

//on other file
const auth = require('../middleware/auth');
router.get('/products', auth, (req, res) => {
    initialPage.getBusinesses(res);
});

const initialPage = {
    getBusinesses(response) {
        ref.orderByKey()
        .limitToLast(20)
        .on('value', function(snapshot){
            response.json(snapshot.val()); 
            return snapshot.val();
        })
    }
}

  searchApi = async() => {
        const response = await axios.get('http://33c75838823c90.ngrok.io/api/v1/products',{
                headers: {
                    "Content-Type": "application/json",
                    "Accept": "application/json",
                    "x-auth-token":"jgiiHDgfdeizI1NiIJ9.eyJfaWQiOiI1ZmEwMWMzZmM4YjIwYjBjZDQyMmJkNzUiLCJpYXQiOjE2MDQ0MTAwMDZ0KwFAgVtsJUQw"
                }
            }
        ).catch((error) => {
            console.log("ERROR FROM AXIOS:", error)
          });
        console.log("RESPONSE DATA: %%%%%%%", response.data)
        this.setState({results: [response.data]});
       
    }

客户端使用React Native

On terminal 401 Unauthorized 

[2020-11-05T13:23:24.421Z]  @firebase/database: FIREBASE WARNING: Exception was thrown by user callback. Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

const getsRoute = require('./routes/gets');
app.use('/api/v1', getsRoute);

//on other file
const auth = require('../middleware/auth');
router.get('/products', auth, (req, res) => {
    initialPage.getBusinesses(res);
});

const initialPage = {
    getBusinesses(response) {
        ref.orderByKey()
        .limitToLast(20)
        .on('value', function(snapshot){
            response.json(snapshot.val()); 
            return snapshot.val();
        })
    }
}

  searchApi = async() => {
        const response = await axios.get('http://33c75838823c90.ngrok.io/api/v1/products',{
                headers: {
                    "Content-Type": "application/json",
                    "Accept": "application/json",
                    "x-auth-token":"jgiiHDgfdeizI1NiIJ9.eyJfaWQiOiI1ZmEwMWMzZmM4YjIwYjBjZDQyMmJkNzUiLCJpYXQiOjE2MDQ0MTAwMDZ0KwFAgVtsJUQw"
                }
            }
        ).catch((error) => {
            console.log("ERROR FROM AXIOS:", error)
          });
        console.log("RESPONSE DATA: %%%%%%%", response.data)
        this.setState({results: [response.data]});
       
    }

我在论坛上查阅了这么多文档和问题，但没有人能找到适合一般问题的解决方案。
问题在这里：

getBusinesses(response) {
    ref.orderByKey()
    .limitToLast(20)
    .on('value', function(snapshot){
        response.json(snapshot.val()); 
        return snapshot.val();
    })
}

由于您正在（…）

上使用

，因此将调用您的回调：

数据一加载
在此之后，数据随时发生变化
第一个响应按预期工作，但是如果数据发生变化，这意味着您正在尝试发送另一个响应，这就是导致错误的原因

要解决此问题，请使用
一次，而不是
上的
：

getBusinesses(response) {
    ref.orderByKey()
    .limitToLast(20)
    .once('value', function(snapshot){
        response.json(snapshot.val()); 
        return snapshot.val();
    })
}

这是一个API问题，不需要包含客户端代码。我遇到过这个问题，但是每个人提到的答案我都不明白，也许我对这个概念还比较陌生，如果你能告诉我确切的解决方案，那会更有帮助。感谢@NarenCan向您提供有关处理此路由的代码、路由、中间件的更多详细信息使用此路由器。get（'/products'，auth，（req，res）=>{initialPage.getbusinesss（res）；}）；谢谢你，弗兰克先生，这些天你救了我很多。