我们正在开发一个应用程序，我们将Firebase用作数据库，并表示作为中间件/后端，用于路由我们在Reactjs中开发的前端使用的RESTful API。
以下是我们的server.js文件：
var express = require('express');
var app = express();
//Used for getting POST variables from forms as well as query parameters
var bodyParser = require('body-parser');
var validator = require('express-validator');
//Contains all the routes
var routes = require('./routes/routes');
var path = require('path');
//Used for serving jade files
app.set('view engine', 'jade');
//For serving static resources like scripts, styleSheets, html
app.use(express.static(__dirname + '/views'));
app.all('/*', function(req, res, next) {
res.header("Access-Control-Allow-Origin", "*");
res.header("Access-Control-Allow-Headers", "X-Requested-With, Content-Type, Accept");
res.header("Access-Control-Allow-Methods", "POST, GET");
next();
});
// configure app to use bodyParser()
// this will let us get the data from a POST
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use(validator({
customValidators: {
onlyAlphabets: function(value) {
if (value.match('^[a-zA-Z ]*$')) {
return true;
} else {
return false;
}
},
password: function(value) {
if (value.length >= 6 && value.length <=25 && value.match('^[\x20-\x7F]*$')) {
return true;
} else {
return false;
}
}
}
}));
app.use(routes);
var port = process.env.PORT || 8080; //Set our port
app.listen(port);
console.log('Magic happens on port ' + port);
以下是route.js中的路由代码：
var express = require('express');
var views = __dirname;
// Node.js path library - https://nodejs.org/api/path.html
var path = require('path');
var Firebase = require("firebase");
var myFirebaseRef = new Firebase("https://crackling-inferno-8454.firebaseio.com/vendor_details");
var router = express.Router();
//Password Encryption and decryption helpers
var hashFunction = require('../helpers/encrypt');
// middleware to use for all requests
router.use(function(req, res, next) {
// do logging
console.log('Something is happening.');
next(); // make sure we go to the next routes and don't stop here
});
router.get('/', function(req, res) {
res.render('vendor_form');
});
router.route('/get_vendors').get(function(request, response) {
myFirebaseRef.on("value", function(snapshot) {
var store = snapshot.val();
// Looping to get the firebaseId generated while push
for(var key in store){
store[key].id = key; // Store firebaseID generated during push to store in JSON object
}
response.send(Object.keys(store).map(function(k) { return store[k]; }));
}, function (errorObject) {
response.send("The read failed: " + errorObject.code);
});
});
router.route('/post_vendor').post(function(request, response) {
request.checkBody({
'vendor_name': {
notEmpty : {
errorMessage: 'Please enter a vendor\'s name'
},
onlyAlphabets : {
errorMessage: 'Please enter only alphabets'
}
},
'enterprise_name': {
notEmpty : {
errorMessage: 'Please enter an enterprise\'s name'
},
onlyAlphabets : {
errorMessage: 'Please enter only alphabets'
}
},
'vendor_email': {
notEmpty : {
errorMessage: 'Please enter your email address'
},
isEmail : {
errorMessage: 'please enter an appropriate email format'
}
},
'vendor_password': {
notEmpty : {
errorMessage: 'Please enter a password'
},
password: {
errorMessage: 'Password length should be between 6-25 characters'
}
},
'food_preference': {
notEmpty: {
errorMessage: 'You must select atleast one food preference'
}
}
});
var errors = request.validationErrors();
// var onComplete = function(error) {
// if (error) {
// response.send('Failed to add stats to the database');
// return false;
// } else {
// // response.render('vendor_form', { success: true });
// response.send('Success');
// return true;
// }
// };
if (errors) {
response.send(errors);
// response.render('vendor_form', { error: errors });
return false;
} else {
myFirebaseRef.push().set({
'id': Firebase.ServerValue.TIMESTAMP,
'vendor_name': request.body.vendor_name,
'enterprise_name': request.body.enterprise_name,
'vendor_email': request.body.vendor_email,
'vendor_password': hashFunction.encrypt(request.body.vendor_password),
'food_preference': request.body.food_preference
}, function(err) {
if (err) {
response.send('Failed to add stats to the database');
} else {
response.send('Success');
}
});
return true;
}
});
module.exports = router;
以下是我们在前端添加的用于发布数据的代码。我们也在使用whatwg-fetch包：
httpservice.js：
var Fetch = require('whatwg-fetch');
var baseUrl = 'http://192.168.1.134:8080';
var Service = {
get: function(url) {
console.log('MAKING A GET REQUEST');
return fetch(baseUrl + url)
.then(function(response) {
return response.json();
});
},
post: function(url, postData) {
console.log('MAKING A POST REQUEST');
return fetch(baseUrl + url, {
headers: {
'Content-Type': 'application/json'
},
method: 'POST',
body: JSON.stringify(postData)
}).then(function(response) {
return response;
});
}
}
module.exports = Service;
VendorForm.js（React组件文件）
HTTP.post('/post_vendor', httpRequestBody)
.then(function(response) {
console.log(response);
}.bind(this));
我们启动服务器，它通过 nodemon 提供在FIREBASE + EXPRESS中开发的RESTful API。这是我们发布时的错误：
FIREBASE WARNING: Exception was thrown by user callback. Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:344:11)
at ServerResponse.header (/var/www/tutorials/express_firebase/node_modules/express/lib/response.js:718:10)
at ServerResponse.send (/var/www/tutorials/express_firebase/node_modules/express/lib/response.js:163:12)
at ServerResponse.json (/var/www/tutorials/express_firebase/node_modules/express/lib/response.js:249:15)
at ServerResponse.send (/var/www/tutorials/express_firebase/node_modules/express/lib/response.js:151:21)
at /var/www/tutorials/express_firebase/routes/routes.js:30:12
at /var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:200:710
at ec (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:52:165)
at ac (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:31:216)
at bc (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:30:1259)
at Ji.h.Mb (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:220:440)
at X.set (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:256:335)
at /var/www/tutorials/express_firebase/routes/routes.js:96:24
at Layer.handle [as handle_request] (/var/www/tutorials/express_firebase/node_modules/express/lib/router/layer.js:95:5)
at next (/var/www/tutorials/express_firebase/node_modules/express/lib/router/route.js:131:13)
at Route.dispatch (/var/www/tutorials/express_firebase/node_modules/express/lib/router/route.js:112:3)
/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:52
(d="0"+d),c+=d;return c.toLowerCase()}var zd=/^-?\d{1,10}$/;function td(a){return zd.test(a)&&(a=Number(a),-2147483648<=a&&2147483647>=a)?a:null}function ec(a){try{a()}catch(b){setTimeout(function(){R("Exception was thrown by user callback.",b.stack||"");throw b;},Math.floor(0))}}function S(a,b){if(t(a)){var c=Array.prototype.slice.call(arguments,1).slice();ec(function(){a.apply(null,c)})}};function Ad(a){var b={},c={},d={},e="";try{var f=a.split("."),b=Pb(id(f[0])||""),c=Pb(id(f[1])||""),e=f[2],d=c.d||{};delete c.d}catch(g){}return{oh:b,Dc:c,data:d,ah:e}}function Bd(a){a=Ad(a).Dc;return"object"===typeof a&&a.hasOwnProperty("iat")?z(a,"iat"):null}function Cd(a){a=Ad(a);var b=a.Dc;return!!a.ah&&!!b&&"object"===typeof b&&b.hasOwnProperty("iat")};function Dd(a){this.Y=a;this.g=a.n.g}function Ed(a,b,c,d){var e=[],f=[];Na(b,function(b){"child_changed"===b.type&&a.g.Ad(b.Le,b.Ma)&&f.push(new H("child_moved",b.Ma,b.Ya))});Fd(a,e,"chi
Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:344:11)
at ServerResponse.header (/var/www/tutorials/express_firebase/node_modules/express/lib/response.js:718:10)
at ServerResponse.send (/var/www/tutorials/express_firebase/node_modules/express/lib/response.js:163:12)
at ServerResponse.json (/var/www/tutorials/express_firebase/node_modules/express/lib/response.js:249:15)
at ServerResponse.send (/var/www/tutorials/express_firebase/node_modules/express/lib/response.js:151:21)
at /var/www/tutorials/express_firebase/routes/routes.js:30:12
at /var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:200:710
at ec (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:52:165)
at ac (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:31:216)
at bc (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:30:1259)
at Ji.h.Mb (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:220:440)
at X.set (/var/www/tutorials/express_firebase/node_modules/firebase/lib/firebase-node.js:256:335)
at /var/www/tutorials/express_firebase/routes/routes.js:96:24
at Layer.handle [as handle_request] (/var/www/tutorials/express_firebase/node_modules/express/lib/router/layer.js:95:5)
at next (/var/www/tutorials/express_firebase/node_modules/express/lib/router/route.js:131:13)
at Route.dispatch (/var/www/tutorials/express_firebase/node_modules/express/lib/router/route.js:112:3)
[nodemon] app crashed - waiting for file changes before starting...
根据错误，我们知道某些回调是设置标题两次但不确定它是如何发生的。经过几次堆栈溢出问题，但仍未找到解决方案。任何帮助，将不胜感激。感谢您的期待。
答案 0 :(得分：8)
如果您看到堆栈跟踪
at /var/www/tutorials/express_firebase/routes/routes.js:30:12
这是文件route.js中的第30行
response.send(Object.keys(store).map(function(k) { return store[k]; }));
您需要为on更改方法once，否则每次更新数据时都会触发回调函数，
router.route('/get_vendors').get(function(request, response) {
myFirebaseRef.on("value", function(snapshot) {
在您调用post方法时中断响应，因为标题已在第30行发送。
参见参考https://firebase.google.com/docs/database/server/retrieve-data#section-reading-once
基本上你使用once方法正在做的是在读取值后立即删除回调。