Why is AJAX returning HTTP status code 0

Question

For some reason  while using AJAX  with my dashcode developed application  the browser just stops uploading and returns status codes of 0  Why does this happen

User · Answer

Observe the browser Console while making the request  if you are seeing  The Same Origin Policy disallows reading the remote resource at http ajax      reason  cors header    access-control-allow-origin    missing  then you need to add  Access-Control-Allow-Origin  in response header  exa  in java you can set this like response setHeader  Access-Control-Allow-Origin        where response is HttpServletResponse

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This article helped me  I was submitting form via AJAX and forgotten to use return false  after my ajax request  which led to classic form submission but strangely it was not completed

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Same problem here when using  lt button onclick    gt submit lt  button gt   Then solved by using  lt input type  button  onclick    gt

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In my case  setting url     in ajax settings would result in a status code 0 in ie8   It seems ie just doesn t tolerate such a setting

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Because this shows up when you google ajax status 0 I wanted to leave some tip that just took me hours of wasted time     I was using ajax to call a PHP service which happened to be Phil s REST Controller for Codeigniter  not sure if this has anything to do with it or not  and kept getting status 0  readystate 0 and it was driving me nuts  I was debugging it and noticed when I would echo and return instead of exit the message I d get a success  Finally I turned debugging off and tried and it worked  Seems the xDebug debugger with PHP was somehow modifying the response  If your using a PHP debugger try turning it off to see if that helps

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We had similar problem - status code 0 on jquery ajax call - and it took us whole day to diagnose it  Since no one had mentioned this reason yet  I thought I ll share   In our case the problem was HTTP server crash  Some bug in PHP was blowing Apache  so on client end it looked like this   mirek toccata    telnet our server com 80 Trying 180 153 xxx xxx    Connected to our server com  Escape character is       GET  test php HTTP 1 0 Host  our server com  Connection closed by foreign host  mirek toccata       where test php contained the crashing code  No data returned from the server  not even headers     ajax call was aborted with status 0

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In our case  the page link was changed from https to http  Even though the users were logged in  they were prevented from loading with AJAX

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In my troubleshooting  I found this AJAX xmlhttpRequest status    0 could mean the client call had NOT reached the server yet  but failed due to issue on the client side  If the response was from server  then the status must be either those 1xx 2xx 3xx 4xx 5xx HTTP Response code  Henceforth  the troubleshooting shall focus on the CLIENT issue  and could be internet network connection down or one of those described by  Langdon above

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I think I know what may cause this error   In google chrome there is an in-built feature to prevent ddos attacks for google chrome extensions   When ajax requests continuously return 500  status errors  it starts to throttle the requests   Hence it is possible to receive status 0 on following requests

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Status code 0 means the requested url is not reachable  By changing http   something something to https   something something worked for me  IE throwns an error saying  permission denied  when the status code is 0  other browsers dont

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In an attempt to win the prize for most dumbest reason for the problem described   Forgetting to call   xmlhttp send      yes  you need this pivotal line    Yes  I was still getting status returns of zero from the  open  call

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For me  the problem was caused by the hosting company  Godaddy  treating POST operations which had substantial response data  anything more than tens of kilobytes  as some sort of security threat  If more than 6 of these occurred in one minute  the host refused to execute the PHP code that responded to the POST request during the next minute  I m not entirely sure what the host did instead  but I did see  with tcpdump  a TCP reset packet coming as the response to a POST request from the browser  This caused the http status code returned in a jqXHR object to be 0   Changing the operations from POST to GET fixed the problem  It s not clear why Godaddy impose this limit  but changing the code was easier than changing the host

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I found another case where jquery gives you status code 0 -- if for some reason XMLHttpRequest is not defined  you ll get this error   Obviously this won t normally happen on the web  but a bug in a nightly firefox build caused this to crop up in an add-on I was writing

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In my experience  you ll see a status of 0 when    doing cross-site scripting  where access is denied  requesting a URL that is unreachable  typo  DNS issues  etc  the request is otherwise intercepted  check your ad blocker  as above  if the request is interrupted  browser navigates away from the page

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Accidental  form submission was exactly the problem I was having  I just removed the FORM tags altogether and that seems to fix the problem  Thank you  everybody

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In my case  I was making a Firefox Add-on and forgot to add the permission for the url domain I was trying to ajax  hope this saves someone a lot of time

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Another case   It could be possible to get a status code of 0 if you have sent an AJAX call and a refresh of the browser was triggered before getting the AJAX response  The AJAX call will be cancelled and you will get this status

User · Answer

I had the same problem  and it was  related to XSS  cross site scripting  block by the browser  I managed to make it work using a server   Take a look at  http   www daniweb com web-development javascript-dhtml-ajax threads 282972 why-am-i-getting-xmlhttprequest status0

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In my case  I was getting this but only on Safari Mobile  The problem is that I was using the full URL  http   example com whatever php  instead of the relative one  whatever php   This doesn t make any sense though  it can t be a XSS issue because my site is hosted at http   example com  I guess Safari looks at the http part and automatically flags it as an insecure request without inspecting the rest of the URL

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In my case  it was caused by running my django server under http   127 0 0 1 8000  but sending the ajax call to http   localhost 8000   Even though you would expect them to map to the same address  they don t so make sure you re not sending your requests to localhost

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It is important to note  that ajax calls can fail even within a session which is defined by a cookie with a certain domain prefixed with www  When you then call your php script e g  without the www  prefix in the url  the call will fail and viceversa  too

[ajax] Why is AJAX returning HTTP status code 0?

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