Error Can t set headers after they are sent to the client

Question

I m fairly new to Node js and I am having some issues   I am using Node js 4 10 and Express 2 4 3   When I try to access http   127 0 0 1 8888 auth facebook  i ll be redirected to http   127 0 0 1 8888 auth facebook callback   I then received the following error   Error  Can t render headers after they are sent to the client      at ServerResponse  lt anonymous gt   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   lt anonymous gt    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  lt anonymous gt   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  lt anonymous gt   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  lt anonymous gt   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  lt anonymous gt   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  lt anonymous gt   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  lt anonymous gt    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    The following is my code   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     May I know what is wrong with my code

User · Answer

In my case it was a 304 response  caching  that was causing the issue     Easiest solution   app disable  etag      Alternate solution here if you want more control   http   vlasenko org 2011 10 12 expressconnect-static-set-last-modified-to-now-to-avoid-304-not-modified

User · Answer

This error happens when you send 2 responses  For example    if condition A            res render  Profile    client client         if  condition B          res render  Profile    client client                 Imagine if for some reason condition A and B are true so in the second render you ll get that error

User · Answer

Came here from nuxt  the problem was in the component s asyncData method  I forgot to return promise which was fetching data and setting header there

User · Answer

Please search if in your app get to not set status before res send  quot your result quot    I just removed   res sendStatus 200    and response works after that     res send  quot your result quot

User · Answer

Some of the answers in this Q amp A are wrong  The accepted answer is also not very  practical   so I want to post an answer that explains things in simpler terms  My answer will cover 99  of the errors I see posted over and over again  For the actual reasons behind the error take a look at the accepted answer     HTTP uses a cycle that requires one response per request  When the client sends a request  e g  POST or GET  the server should only send one response back to it   This error message      Error  Can t set headers after they are sent    usually happens when you send several responses for one request  Make sure the following functions are called only once per request    res json   res send   res redirect   res render      and a few more that are rarely used  check the accepted answer   The route callback will not return when these res functions are called  It will continue running until it hits the end of the function or a return statement  If you want to return when sending a response you can do it like so  return res send       Take for instance this code   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          When a POST request is sent to  api route1 it will run every line in the callback  A Can t set headers after they are sent error message will be thrown because res json   is called twice  meaning two responses are sent   Only one response can be sent per request     The error in the code sample above was obvious  A more typical problem is when you have several branches   app get   api company  companyId   function req  res      const   companyId     req params    Company findById companyId  exec  err  company    gt          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              This route with attached callback finds a company in a database  When doing a query for a company that doesn t exist we will get inside the else if branch and send a 404 response  After that  we will continue on to the next statement which also sends a response  Now we have sent two responses and the error message will occur  We can fix this code by making sure we only send one response    exec  err  company    gt      if  err        res status 500  json err       else if   company        res status 404  json               Only this runs      else       res status 200  json company             or by returning when the response is sent    exec  err  company    gt      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           A big sinner is asynchronous functions  Take the function from this question  for example   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            Here we have an asynchronous function  findOneAndUpdate    in the code sample  If there are no errors  err  findOneAndUpdate   will be called  Because this function is asynchronous the res json doc1  will be called immediately  Assume there are no errors in findOneAndUpdate    The res json doc2  in the else will then be called  Two responses have now been sent and the Can t set headers error message occurs   The fix  in this case  would be to remove the res json doc1   To send both docs back to the client the res json   in the else could be written as res json   article  doc1  user  doc2

User · Answer

My issue was that I had a setInterval running  which had an if else block  where the clearInterval method was inside the else         const dataExistsInterval   setInterval async      gt            const dataExists   Object keys req body  length     0          if  dataExists              if   req files length                return res json   msg  false                 else                 clearInterval dataExistsInterval               try                       Putting the clearInterval before the if else did the trick

User · Answer

In my case  In a loop  I put res render   so might have been tried to call multiple times

User · Answer

In my case it happens due to multiple callbacks  I have called next   method multiple time during the code

User · Answer

I ran into this error as well for a while   I think  hope  I ve wrapped my head around it  wanted to write it here for reference   When you add middleware to connect or express  which is built on connect  using the app use method  you re appending items to Server prototype stack in connect  At least with the current npm install connect  which looks quite different from the one github as of this post    When the server gets a request  it iterates over the stack  calling the  request  response  next  method   The problem is  if in one of the middleware items writes to the response body or headers  it looks like it s either or for some reason   but doesn t call response end   and you call next   then as the core Server prototype handle method completes  it s going to notice that    there are no more items in the stack  and or that response headerSent is true    So  it throws an error   But the error it throws is just this basic response  from the connect http js source code   res statusCode   404  res setHeader  Content-Type    text plain    res end  Cannot     req method         req url     Right there  it s calling res setHeader  Content-Type    text plain     which you are likely to have set in your render method  without calling response end    something like   response setHeader  Content-Type    text html    response write   lt p gt Hello World lt  p gt       The way everything needs to be structured is like this   Good Middleware     middleware that does not modify the response body var doesNotModifyBody   function request  response  next      request params         a   b            calls next because it hasn t modified the header   next           middleware that modify the response body var doesModifyBody   function request  response  next      response setHeader  Content-Type    text html      response write   lt p gt Hello World lt  p gt       response end         doesn t call next       app use doesNotModifyBody   app use doesModifyBody     Problematic Middleware  var problemMiddleware   function request  response  next      response setHeader  Content-Type    text html      response write   lt p gt Hello World lt  p gt       next         The problematic middleware sets the response header without calling response end   and calls next    which confuses connect s server

User · Answer

For anyone that s coming to this and none of the other solutions helped  in my case this manifested on a route that handled image uploading but didn t handle timeouts  and thus if the upload took too long and timed out  when the callback was fired after the timeout response had been sent  calling res send   resulted in the crash as the headers were already set to account for the timeout   This was easily reproduced by setting a very short timeout and hitting the route with a decently-large image  the crash was reproduced every time

User · Answer

All I had to do in case of this error was res end      auth annonymousOnly   function req  res  next        add other task here       res end               The other problem you could be facing is there is code after res json and res  write  In this case  you need to use return to stop execution after that    auth annonymousOnly   function req  res  next       if  req body name          res json  error  some error         return        let comp    value      this is the code after res json which may cause some problems so you have to use return

User · Answer

Please check if your code is returning multiple res send   statements for a single request  Like when I had this issue     I was this issue in my restify node application  The mistake was that switch  status        case -1        res send 400       case 0        res send 200       default        res send 500      I was handling various cases using switch without writing break  For those little familiar with switch case know that without break  return keywords  The code under case and next lines of it will be executed no matter what  So even though I want to send single res send  due to this mistake it was returning multiple res send statements  which prompted  error  can t set headers after they are sent to the client   Which got resolved by adding this or using return before each res send   method like return res send 200  switch  status        case -1        res send 400         break      case 0        res send 200         break      default        res send 500         break

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Process env does not change  so it must not be used for accessing per-request environment variables whose values may change on a per-request basis  So  if the user spawns an application process  but not as part of handling a request  then that application process will not have per-request environment variables stored inside OS-level environment variables  So  use this code to store process env and your program run successfully      const port   process env PORT    2000           app listen port     gt           console log  quot Server running at port 2000 quot

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error find by itself after a  RND    1  my error code    return res sendStatus 200  json   data  result      2  my success code  return res status 200  json   data  result      the difference is that i used sendStatus   instead of status

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I had this same issue and realised it was because I was calling res redirect without a return statement  so the next function was also being called immediately afterwards   auth annonymousOnly   function req  res  next        if  req user  res redirect           next         Which should have been   auth annonymousOnly   function req  res  next        if  req user  return res redirect           next

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This type of error you will get when you pass statements after sending a response   For example          res send  something response    console log  jhgfjhgsdhgfsdf    console log  sdgsdfhdgfdhgsdf    res send  sopmething response      Will result in the error you are seeing  because once the response has been sent  the following res send will not be executed   If you want do anything  you should do it before sending the response

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The res object in Express is a subclass of Node js s http ServerResponse  read the http js source   You are allowed to call res setHeader name  value  as often as you want until you call res writeHead statusCode   After writeHead  the headers are baked in and you can only call res write data   and finally res end data   The error  quot Error  Can t set headers after they are sent  quot  means that you re already in the Body or Finished state  but some function tried to set a header or statusCode  When you see this error  try to look for anything that tries to send a header after some of the body has already been written  For example  look for callbacks that are accidentally called twice  or any error that happens after the body is sent  In your case  you called res redirect    which caused the response to become Finished  Then your code threw an error  res req is null   and since the error happened within your actual function req  res  next   not within a callback   Connect was able to catch it and then tried to send a 500 error page  But since the headers were already sent  Node js s setHeader threw the error that you saw  Comprehensive list of Node js Express response methods and when they must be called  Response must be in Head and remains in Head   res writeContinue   res statusCode   404 res setHeader name  value  res getHeader name  res removeHeader name  res header key   val    Express only  res charset    utf-8   Express only  only affects Express-specific methods  res contentType type   Express only   Response must be in Head and becomes Body   res writeHead statusCode   reasonPhrase    headers    Response can be in either Head Body and remains in Body   res write chunk  encoding  utf8    Response can be in either Head Body and becomes Finished   res end  data    encoding    Response can be in either Head Body and remains in its current state   res addTrailers headers   Response must be in Head and becomes Finished   return next  err    Connect Express only  Any exceptions within middleware function req  res  next   Connect Express only  res send body status   headers status   status     Express only  res attachment filename   Express only  res sendfile path   options   callback     Express only  res json obj   headers status   status     Express only  res redirect url   status    Express only  res cookie name  val   options    Express only  res clearCookie name   options    Express only  res render view   options   fn     Express only  res partial view   options    Express only

User · Answer

I had the same problem which was caused by mongoose   to fix that you must enable Promises  so you can add   mongoose Promise   global Promise to your code which enables using native js promises   other alternatives to this soloution is    var mongoose   require  mongoose       set Promise provider to bluebird mongoose Promise   require  bluebird      and     q mongoose Promise   require  q   Promise    but you need to install these packages first

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Add this middlware and it will work  app use function req res next    var  send   res send  var sent   false  res send   function data       if sent  return       send bind res  data       sent   true     next

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I simply add the return key word like  return res redirect   great    and walla

User · Answer

Lots of people hit this error   It s a confusing this with async processing   Most likely some of your code is setting headers in the first tick and then you are running an async callback in a future tick  In between  the response header gets sent  but then further headers  like a 30X redirect  try to add extra headers  but it s too late since the response header has already been transmitted   I m not sure exactly what s causing your error  but look at any callbacks as potential areas to investigate   One easy tip to simplify your code  Get rid of app configure   and just call app use directly in your top level scope   See also the everyauth module  which does Facebook and a dozen or so other 3rd party authentication providers

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I had this issue when I was nesting promises  A promise inside of a promise would return 200 to the server  but then the outer promise s catch statement would return a 500  Once I fixed this  the problem went away

User · Answer

If you din t get help from above   for noobs  The reason behind this error is sending request multiple times let us understand from some cases -  1        module exports    req res next   gt           try             const decoded    jwt verify req body token  secret               req userData   decoded             next             catch error               return res status 401  json  message  Auth failed                       next                     in the above calling next   twice will raise an error    router delete    orderId    req  res  next    gt            Order remove   id req params orderId   err data   gt               if err                     res status 500  json err                  else                  res status 200  json data                              res status 200  json data                         here respond is send twice check whether you already sent a response

User · Answer

It is very likely that this is more of a node thing  99  of the time it s a double callback causing you to respond twice  or next  ing twice etc  damn sure  It solved my problem was using next   inside a loop  Remove the next   from the loop or stop calling it more than one times

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Sometimes you may get this error when you try to call next   function after res end or res send   try to delete if you have next   after res send or res end in your function  Note  here next   means after responding to the client with your response i e res send or res end  you are still trying to execute some code to respond again so it is not legal   Example     router get     function  req res next        res send  request received         next       this will give you the above exception           remove next   from above function and it will work

User · Answer

In Typescript  my issue was I didn t close the websocket connection after receiving a message   WebSocket on  message    data    gt        receivedMessage   true      doSomething data       localSocket close      This close the connection  allowing

User · Answer

I got a similar error when I tried to send response within a loop function  The simple solution was to move the      res send  send response      out of the loop since you can only send response header once    https   www tutorialspoint com nodejs nodejs response object htm

User · Answer

I boiled my head over this issue and it has happened due to a careless mistake on handling the callbacks  non returned callbacks cause the response to be set twice    My program had a code which validate request and query the DB  after validating if error is there   I was calling back the index js with the validation errors    And if validation passes it goes ahead and hit the db with success failure        var error   validateRequestDetails  create  queryReq       if  error          callback error  null      else     some code      callback null  success     What was happening is   Incase validation fails the callback get called and response get set  But not returned  So it still continues the method goes to db and hit success failure   It  calls the same callback again causing the response to be set twice now    So solution is simple  you need to  return  the callback so that the method don t continue executing  once the error has occurred and hence set the response object once     var error   validateRequestDetails  create  queryReq       if  error          callback error  null           return      else        some code         callback null  success

User · Answer

If you are using callback functions use return after the err block  This is one of the scenarios in which this error can happen   userModel createUser data  function err  data        if err          res status   422       res json err        return    without this return the error can happen            return res json data         Tested on Node version v10 16 0 and express 4 16 4

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Just leaned this  You can pass the responses through this function   app use function req res next     var  send   res send    var sent   false    res send   function data       if sent  return       send bind res  data       sent   true       next

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In my case this happened with React and postal js when I didn t unsubscribe from a channel in the componentWillUnmount callback of my React component

User · Answer

there is something else that cause this error and it  is when you do not add return keyword in front of res send  res json  etc

User · Answer

This happens when response was delivered to client and again you are trying to give response  You have to check in your code that somewhere you are returning response to client again which causes this error  Check and return response once when you want to return

[javascript] Error: Can't set headers after they are sent to the client

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