Express/Node - 在响应已发送给客户端之后无法设置响应头
Express/Node - 在响应已发送给客户端之后无法设置响应头
我对Node.js相当新，我遇到了一些问题。
我使用的是Node.js 4.10和Express 2.4.3。
当我尝试访问http://127.0.0.1:8888/auth/facebook时，我会被重定向到http://127.0.0.1:8888/auth/facebook_callback。
然后我收到了以下错误：
Error: Can't render headers after they are sent to the client.
at ServerResponse. (http.js:573:11)
at ServerResponse._renderHeaders (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:64:25)
at ServerResponse.writeHead (http.js:813:20)
at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/auth.strategies/facebook.js:28:15
at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/index.js:113:13
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/strategyExecutor.js:45:39)
at [object Object].pass (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/authExecutionScope.js:32:3)
at [object Object].halt (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/authExecutionScope.js:29:8)
at [object Object].redirect (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/authExecutionScope.js:16:8)
at [object Object]. (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/auth.strategies/facebook.js:77:15)
Error: Can't set headers after they are sent.
at ServerResponse. (http.js:527:11)
at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:195:11)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:150:23)
at param (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:189:13)
at pass (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:191:10)
at Object.router [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:197:6)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
at Object.auth [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/index.js:153:7)
Error: Can't set headers after they are sent.
at ServerResponse. (http.js:527:11)
at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:207:9)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:150:23)
at param (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:189:13)
at pass (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:191:10)
at Object.router [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:197:6)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
at Object.auth [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/index.js:153:7)
Error: Can't set headers after they are sent.
at ServerResponse. (http.js:527:11)
at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:150:23)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:207:9)
at Object.auth [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/index.js:153:7)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
at HTTPServer.handle (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:211:3)
at Object.handle (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:105:14)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
Error: Can't set headers after they are sent.
at ServerResponse. (http.js:527:11)
at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:150:23)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:207:9)
at HTTPServer.handle (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:211:3)
at Object.handle (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:105:14)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session.js:323:9
at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session.js:338:9
node.js:134
throw e; // process.nextTick error, or 'error' event on first tick
^
Error: Can't set headers after they are sent.
at ServerResponse. (http.js:527:11)
at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:207:9)
at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session.js:323:9
at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session.js:338:9
at Array. (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session/memory.js:57:7)
at EventEmitter._tickCallback (node.js:126:26)
以下是我的代码：
var fbId= "XXX";
var fbSecret= "XXXXXX";
var fbCallbackAddress= "http://127.0.0.1:8888/auth/facebook_callback"
var cookieSecret = "node"; // enter a random hash for security
var express= require('express');
var auth = require('connect-auth')
var app = express.createServer();
app.configure(function(){
app.use(express.bodyParser());
app.use(express.methodOverride());
app.use(express.cookieParser());
app.use(express.session({secret: cookieSecret}));
app.use(auth([
auth.Facebook({
appId : fbId,
appSecret: fbSecret,
callback: fbCallbackAddress,
scope: 'offline_access,email,user_about_me,user_activities,manage_pages,publish_stream',
failedUri: '/noauth'
})
]));
app.use(app.router);
});
app.get('/auth/facebook', function(req, res) {
req.authenticate("facebook", function(error, authenticated) {
if (authenticated) {
res.redirect("/great");
console.log("ok cool.");
console.log(res['req']['session']);
}
});
});
app.get('/noauth', function(req, res) {
console.log('Authentication Failed');
res.send('Authentication Failed');
});
app.get('/great', function( req, res) {
res.send('Supercoolstuff');
});
app.listen(8888);
请问我的代码有什么问题吗？
admin 更改状态以发布 2023年5月24日
Q&A中的一些答案是错误的。已接受的答案也不太“实用”，因此我想发表一个解释事情更简单的答案。我的答案将涵盖99％反复发布的错误。有关错误背后的实际原因，请查看已接受的答案。
HTTP使用一个循环，需要每次请求一个响应。当客户端发送请求（例如POST或GET）时，服务器只应向其发送一个响应。
通常情况下，当您为一个请求发送多个响应时，会出现以下错误消息：
Error: Can't set headers after they are sent.
确保每个请求仅调用以下功能一次：
res.json()res.send()res.redirect()res.render()
（还有一些很少使用的功能，请查看已接受的答案）
当调用这些res函数时，路由回调不会返回。它将继续运行，直到达到函数的末尾或返回语句。如果要在发送响应时返回，可以这样做：return res.send()。
以这段代码为例：
app.post('/api/route1', function(req, res) {
console.log('this ran');
res.status(200).json({ message: 'ok' });
console.log('this ran too');
res.status(200).json({ message: 'ok' });
}
当向/api/route1发送POST请求时，它将运行回调中的每一行。因为调用res.json()两次，即已发送两个响应，将引发一个Can't set headers after they are sent错误消息。
每个请求只能发送一个响应！
上述代码示例中的错误很明显。更典型的问题是当您有多个分支时：
app.get('/api/company/:companyId', function(req, res) {
const { companyId } = req.params;
Company.findById(companyId).exec((err, company) => {
if (err) {
res.status(500).json(err);
} else if (!company) {
res.status(404).json(); // This runs.
}
res.status(200).json(company); // This runs as well.
});
}
附加回调的此路由在数据库中查找公司。查询不存在的公司时，我们将进入else if分支并发送404响应。此后，我们将继续执行下一个语句，该语句也会发送响应。现在我们已发送了两个响应，将出现错误消息。我们可以通过确保只发送一个响应来修复此代码：
.exec((err, company) => {
if (err) {
res.status(500).json(err);
} else if (!company) {
res.status(404).json(); // Only this runs.
} else {
res.status(200).json(company);
}
});
或在发送响应时返回：
.exec((err, company) => {
if (err) {
return res.status(500).json(err);
} else if (!company) {
return res.status(404).json(); // Only this runs.
}
return res.status(200).json(company);
});
一个大罪犯是异步函数。以此问题的函数为例：
article.save(function(err, doc1) {
if (err) {
res.send(err);
} else {
User.findOneAndUpdate({ _id: req.user._id }, { $push: { article: doc._id } })
.exec(function(err, doc2) {
if (err) res.send(err);
else res.json(doc2); // Will be called second.
})
res.json(doc1); // Will be called first.
}
});
这里我们有一个异步函数（findOneAndUpdate()）在代码示例中。如果没有错误（err），将调用findOneAndUpdate()。由于这个函数是异步的，res.json(doc1)将立即被调用。假设findOneAndUpdate()没有错误。然后将调用else中的res.json(doc2)。现在已发送了两个响应，因此会出现Can't set headers错误消息。
在这种情况下，解决方法是删除res.json(doc1)。为了将两个文档发送回客户端，可以将else中的res.json()写成res.json({ article: doc1, user:doc2})。
在Express中，res对象是Node.js的http.ServerResponse的子类 (可以阅读http.js源代码)。你可以随意调用res.setHeader(name, value)，直到你调用res.writeHead(statusCode)。在调用writeHead之后，头部信息就已经确定了，你只能调用res.write(data)，最后调用res.end(data)。
错误信息"Error: Can't set headers after they are sent."的意思是你已经进入了Body或Finished状态，但某些函数仍然试图设置头部信息或statusCode。当你看到这个错误时，试着查找一下在已经输出了一些body后，有没有任何试图再发送头部信息的东西。例如，可以查找被不小心调用了两次的回调函数，或者在发送了body后发生的任何错误。
在你的情况中，你调用了res.redirect()，这导致响应变成了Finished状态。然后你的代码抛出了一个错误(res.req是null)，并且由于这个错误发生在你的实际function(req, res, next)中(而不是在回调中)，Connect能够捕获它，然后尝试发送一个500错误页面。但由于头部信息已经发送，Node.js的setHeader就抛出了你看到的错误。
Node.js/Express响应方法的综合列表及它们必须被调用的时间:
响应必须在Head状态下，并且保持在Head状态下:
res.writeContinue()res.statusCode = 404res.setHeader(name, value)res.getHeader(name)res.removeHeader(name)res.header(key[, val])(仅限于Express)res.charset = 'utf-8'(仅限于Express；仅影响Express特定的方法)res.contentType(type)(仅限于Express)
响应必须在Head状态下，并且变成Body状态:
响应可以在Head/Body状态下，并且保持在Body状态下:
响应内容可以是头部和主体，当执行完毕后会变成已完成状态：
响应内容可以是头部和主体，且不会改变当前状态：
响应内容必须只为头部，当执行完毕后会变成已完成状态：
return next([err])（仅适用于Connect/Express）- 中间件函数
function(req, res, next)中的任何异常（仅适用于Connect/Express） res.send(body|status[, headers|status[, status]])（仅适用于Express）res.attachment(filename)（仅适用于Express）res.sendfile(path[, options[, callback]])（仅适用于Express）res.json(obj[, headers|status[, status]])（仅适用于Express）res.redirect(url[, status])（仅适用于Express）res.cookie(name, val[, options])（仅适用于Express）res.clearCookie(name[, options])（仅适用于Express）res.render(view[, options[, fn]])（仅适用于Express）res.partial(view[, options])（仅适用于Express）