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I’m currently working on a website, which triggers a net::ERR_HTTP2_PROTOCOL_ERROR 200 error on Google Chrome. I’m not sure exactly what can provoke this error, I just noticed it pops out only when accessing the website in HTTPS. I can’t be 100% sure it is related, but it looks like it prevents JavaScript to be executed properly.

For instance, the following scenario happens :

  1. I’m accessing the website in HTTPS

  2. My Twitter feed integrated via isn’t loaded at all

  3. I can notice in the console the ERR_HTTP2_PROTOCOL_ERROR

  4. If I remove the code to load the Twitter feed, the error remains

  5. If I access the website in HTTP, the Twitter feed appears and the error disappears

Google Chrome is the only web browser triggering the error: it works well on both Edge and Firefox.
(NB: I tried with Safari, and I have a similar kcferrordomaincfnetwork 303 error)

I was wondering if it could be related to the header returned by the server since there is this ‘200’ mention in the error, and a 404 / 500 page isn’t triggering anything.

Thing is the error isn’t documented at all. Google search gives me very few results. Moreover, I noticed it appears on very recent Google Chrome releases; the error doesn’t pop on v.64.X, but it does on v.75+ (regardless of the OS; I’m working on Mac tho).

Might be related to Website OK on Firefox but not on Safari (kCFErrorDomainCFNetwork error 303) neither Chrome (net::ERR_SPDY_PROTOCOL_ERROR)

Findings from further investigations are the following:

  • error doesn’t pop on the exact same page if server returns 404 instead of 2XX
  • error doesn’t pop on local with a HTTPS certificate
  • error pops on a different server (both are OVH’s), which uses a different certificate
  • error pops no matter what PHP version is used, from 5.6 to 7.3 (framework used : Cakephp 2.10)

As requested, below is the returned header for the failing ressource, which is the whole web page. Even if the error is triggering on each page having a HTTP header 200, those pages are always loading on client’s browser, but sometimes an element is missing (in my exemple, the external Twitter feed). Every other asset on the Network tab has a success return, except the whole document itself.
line that failed in console

Google Chrome header (with error):

Chrome header

Firefox header (without error):

Firefox header

A curl --head --http2 request in console returns the following success:

HTTP/2 200 
date: Fri, 04 Oct 2019 08:04:51 GMT
content-type: text/html; charset=UTF-8
content-length: 127089
set-cookie: SERVERID31396=2341116; path=/; max-age=900
server: Apache
x-powered-by: PHP/7.2
set-cookie: xxxxx=0919c5563fc87d601ab99e2f85d4217d; expires=Fri, 04-Oct-2019 12:04:51 GMT; Max-Age=14400; path=/; secure; HttpOnly
vary: Accept-Encoding

Trying to go deeper with the chrome://net-export/ and tools is telling me the request ends with a RST_STREAM :

t=123354 [st=5170]    HTTP2_SESSION_RECV_RST_STREAM
                      --> error_code = "2 (INTERNAL_ERROR)"
                      --> stream_id = 1

For what I read in this other post, "In HTTP/2, if the client wants to abort the request, it sends a RST_STREAM. When the server receives a RST_STREAM, it will stop sending DATA frames to the client, thereby stopping the response (or the download). The connection is still usable for other requests, and requests/responses that were concurrent with the one that has been aborted may continue to progress.
[…] It is possible that by the time the RST_STREAM travels from the client to the server, the whole content of the request is in transit and will arrive to the client, which will discard it. However, for large response contents, sending a RST_STREAM may have a good chance to arrive to the server before the whole response content is sent, and therefore will save bandwidth.

The described behavior is the same as the one I can observe. But that would mean the browser is the culprit, and then I wouldn’t understand why it happens on two identical pages with one having a 200 header and the other a 404 (same goes if I disable JS).



  1. Chosen as BEST ANSWER

    I didn't figure out what exactly was happening, but I found a solution.

    The CDN feature of OVH was the culprit. I had it installed on my host service but disabled for my domain because I didn't need it.

    Somehow, when I enable it, everything works.

    I think it forces Apache to use the HTTP2 protocol, but what I don't understand is that there indeed was an HTTP2 mention in each of my headers, which I presume means the server was answering using the right protocol.

    So the solution for my very particular case was to enable the CDN option on all concerned domains.

    If anyone understands better what could have happened here, feel free to share explanations.

  2. I experienced a similar problem, I was getting ERR_HTTP2_PROTOCOL_ERROR on one of the HTTP GET requests.

    I noticed that the Chrome update was pending, so I updated the Chrome browser to the latest version and the error was gone next time when I relaunched the browser.

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  3. I got the same issue (asp, c# – HttpPostedFileBase) when posting a file that was larger than 1MB (even though application doesn’t have any limitation for file size), for me the simplification of model class helped. If you got this issue, try to remove some parts of the model, and see if it will help in any way. Sounds strange, but worked for me.

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  4. For several weeks I was also annoyed by this “bug”:


    In my case, it occurred on images generated by PHP.

    It was at header() level, and on this one in particular:

    header ('Content-Length:'. Filesize($cache_file));

    It did obviously not return the exact size, so I deleted it and everything works fine now.

    So Chrome checks the accuracy of the data transmitted via the headers, and if it does not correspond, it fails.


    I found why content-length via filesize was being miscalculated: the GZIP compression is active on the PHP files, so excluding the file in question will fix the problem. Put this code in the .htaccess:

    SetEnvIfNoCase Request_URI ^ / thumb.php no-gzip -vary

    It works and we keep the header Content-length.

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  5. I encountered this because the http2 server closed the connection when sending a big response to the Chrome.

    Because it is just a setting of the http2 server, named WriteTimeout.

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  6. I had this problem when having a Nginx server that exposing the node-js application to the external world. The Nginx made the file (css, js, …) compressed with gzip and with Chrome it looked like the same.

    The problem solved when we found that the node-js server is also compressed the content with gzip. In someway, this double compressing leading to this problem. Canceling node-js compression solved the issue.

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  7. I have been experiencing this problem for the last week now as I’ve been trying to send DELETE requests to my PHP server through AJAX. I recently upgraded my hosting plan where I now have an SSL Certificate on my host which stores the PHP and JS files. Since adding an SSL Certificate I no longer experience this issue. Hoping this helps with this strange error.

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  8. In my case it was – no disk space left on the web server.

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  9. I also faced this error and I believe there can be multiple reasons behind it. Mine was, ARR was getting timed-out.

    In my case, browser was making a request to a reverse proxy site where I have set my redirection rules and that proxy site is eventually requesting the actual site. Now for huge data it was taking more than 2 minutes 5 seconds and Application Request Routing timeout for my server was set to 2 minutes. I fixed this by increasing the ARR timeout by below steps:
    1. Go to IIS
    2. Click on server name
    3. Click on Application Request Routing Cache in the middle pane
    4. Click Server Proxy settings in right pane
    5. Increase the timeout
    6. Click Apply

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  10. In our case, the reason was invalid header.
    As mentioned in Edit 4:

    • take the logs
    • in the viewer choose Events
    • chose HTTP2_SESSION

    Look for something similar:


    –> error = "Invalid character in header name."

    –> header_name = "charset=utf-8"

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  11. I faced this error several times and, it was due to transferring large resources(larger than 3MB) from server to client.

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  12. My team saw this on a single javascript file we were serving up. Every other file worked fine. We switched from http2 back to http1.1 and then either net::ERR_INCOMPLETE_CHUNKED_ENCODING or ERR_CONTENT_LENGTH_MISMATCH. We ultimately discovered that there was a corporate filter (Trustwave) that was erroneously detecting an “infoleak” (we suspect it detected something in our file/filename that resembled a social security number). Getting corporate to tweak this filter resolved our issues.

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  13. This error is currently being fixed:

    But it helped me, changing nginx settings:

    • turning on gzip;
    • add_header ‘Cache-Control’ ‘no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0’;
    • expires off;

    In my case, Nginx acts as a reverse proxy for Node.js application.

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  14. We experienced this problem on pages with long Base64 strings. The problem occurs because we use CloudFlare.


    Key section from the forum post:

    After further testing on Incognito tabs on multiple browsers, then
    doing the changes on the code from a BASE64 to a real .png image, the
    issue never happened again, in ANY browser. The .png had around 500kb
    before becoming a base64,so CloudFlare has issues with huge lines of
    text on same line (since base64 is a long string) as a proxy between
    the domain and the heroku. As mentioned before, directly hitting
    Heroku url also never happened the issue.

    The temporary hack is to disable HTTP/2 on CloudFlare.

    Hope someone else can produce a better solution that doesn’t require disabling HTTP/2 on CloudFlare.

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  15. For my situation this error was caused by having circular references in json sent from the server when using an ORM for parent/child relationships. So the quick and easy solution was

    JsonConvert.SerializeObject(myObject, new JsonSerializerSettings { ReferenceLoopHandling = ReferenceLoopHandling.Ignore })

    The better solution is to create DTOs that do not contain the references on both sides (parent/child).

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  16. I am finally able to solve this error after researching some things I thought is causing the error for 24 errors. I visited all the pages across the web. And I am happy to say that I have found the solution.
    If you are using NGINX, then set gzip to off and add proxy_max_temp_file_size 0; in the server block like I have shown below.

     server {
      gzip off;
      proxy_max_temp_file_size 0;
      location / {

    Why? Because what actually happening was all the contents were being compressed twice and we don’t want that, right?!

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  17. By default nginx limits upload size to 1MB.

    With client_max_body_size you can set your own limit, as in

    location /uploads {
        client_max_body_size 100M;

    You can set this setting also on the http or server block instead (See here).

    This fixed my issue with net::ERR_HTTP2_PROTOCOL_ERROR

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  18. I had another case that caused an ERR_HTTP2_PROTOCOL_ERROR that hasn’t been mentioned here yet. I had created a cross reference in IOC (Unity), where I had class A referencing class B (through a couple of layers), and class B referencing class A. Bad design on my part really. But I created a new interface/class for the method in class A that I was calling from class B, and that cleared it up.

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  19. In my case, it was WordPress that now requires PHP 7.4 and I was running 7.2.
    As soon as I updated, the errors disappeared.

    Happened again and this time it was the ad-blocker that didn’t like the name of my images (yt.png, ig.png, url.png). I added a prefix and all loaded ok.

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  20. I hit this issue working with Server Sent Events. The problem was solved when I noticed that the domain name I used to initiate the connection included a trailing slash, e.g. failed with ERR_HTTP_PROTOCOL_ERROR while worked.

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  21. In my case (nginx on windows proxying an app while serving static assets on its own) page was showing multiple assets including 14 bigger pictures; those errors were shown for about 5 of those images exactly after 60 seconds; in my case it was a default send_timeout of 60s making those image requests fail; increasing the send_timeout made it work

    I am not sure what is causing nginx on windows to serve those files so slow – it is only 11.5MB of resources which takes nginx almost 2 minutes to serve but I guess it is subject for another thread

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  22. I’m not convinced this was the issue but through cPanel I’d noticed the PHP version was on 5.6 and changing it to 7.3 seemed to fix it. This was for a WordPress site. I noticed I could access images and generic PHP files but loading WordPress itself caused the error.

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  23. Seems like many issues may cause ERR_HTTP2_PROTOCOL_ERROR: in my case it was a minor syntax error in a php-generated header, Content-Type : text/plain . You might notice the space before the colon… that was it. Works no problem when the colon is right next to the header name like Content-Type: text/plain. Only took a million hours to figure out… The error happens with Chrome only, Firefox loaded the object without complaint.

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  24. If simply restarting e.g., Chrome Canary, with a fresh profile fixes the problem, then one surely
    is the "victim" of a failed Chrome Variation! Yes, there are ways to opt out of being a Guinea pig in Chrome’s field testing.

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  25. In my case
    header params can not set null or empty string

     'Authorization': Authorization  //Authorization can't use null or ''
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  26. For those landing from search engines.

    I had this issue recently, albeit not PHP, rather .NET and Angular. I tried the vast majority of suggestions here and on the MS support forums for IIS etc. In the end I had to reinstall / repair IIS Express via the old control panel (this restores the development certificate, I don’t actually use IIS Express) and disable HTTP/2 under the HTTPS binding for the application. Of course, this is for a development environment only.

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  27. In my case, the problem was that Bitdefender provided me with a local ssl certificate, when the website was still without a certificate.

    When I disabled Bitdefender and reloaded the page, the actual valid server ssl certificate was loaded, and the ERR_HTTP2_PROTOCOL_ERROR was gone.

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  28. The fix for me was setting minBytesPerSecond in IIS to 0. This setting can be found in system.applicationHost/webLimits in IIS’s Configuration Editor. By default it’s set to 240.

    enter image description here

    It turns out that some webservers will cut the connection to a client if the server’s data throughput to the client passes below a certain limit. This is to protect against "slow drip" denial of service attacks. However, this limit can also be triggered in cases where an innocent user requests many resources all at once (such as lots of images on a single page), and the server is forced to ration the bandwidth for each request so much that it causes one or more requests to drop below the throughput limit, which causes the server to cut the connection and shows up as net::ERR_HTTP2_PROTOCOL_ERROR in Chrome.

    For example, let’s say you request 10 GIF images all at once, and each GIF is 10 megabytes (100MB total). If your download speed from the server is 1MB per second, your browser will have to divide that 1MBps amongst the 10 images somehow. Now, here is where it gets interesting, as how the bandwidth gets divided seems to be random:

    1. Your browser may divide the bandwidth equally across the images, resulting in 0.1MBps allocated to each image. None of the download speeds fall below the default IIS minBytesPerSecond limit of 240 bytes, so all the GIFs download successfully.
    2. Your browser may prioritize first 5 at 0.2MBps, and put the last 5 "on hold" at 0MBps, to be downloaded after the first 5. However, since 0MBps is below the default IIS minBytesPerSecond limit of 240 bytes, the server cuts the connection to the remaining downloads.

    I was able to stop the connections from being cut by following these steps:

    1. I used Chrome’s Network Log Export tool at chrome://net-export/ to see exactly what was behind the ERR_HTTP2_PROTOCOL_ERROR error. I started the log, reproduced the error, and stopped the log.
    2. I imported the log into the log viewer at, and saw an interesting event titled HTTP2_SESSION_RECV_RST_STREAM, with error code 8 (CANCEL).

    enter image description here

    1. I did some Googling on the term "RST_STREAM" (which appears to be an abbreviated form of "reset stream") and found a discussion between some people talking about an IIS setting called minBytesPerSecond (discussion here: I also found another discussion where there was some debate about whether minBytesPerSecond was intended to protect against slow HTTP DoS (slow drip) attacks (discussion here: IIS 8.5 low minBytesPerSecond not working against slow HTTP POST). In any case, I learned that IIS uses minBytesPerSecond to determine whether to cancel a connection if it cannot sustain the minimum throughput. This is relevant in cases where a single user makes many requests to a large resource, and each new connection ends up starving all the other unfinished ones, to the point where some may fall below the minBytesPerSecond threshold.
    2. To confirm that the server was canceling requests due to a minBytesPerSecond error, I checked my server’s HTTPERR log at c:windowssystem32logfileshttperr. Sure enough, I opened the file and did a text search for "MinBytesPerSecond" and there were tons of entries for it.

    enter image description here

    1. So after I changed the minBytesPerSecond to 0, I was no longer able to reproduce the ERR_HTTP2_PROTOCOL_ERROR error. So, it appears that the ERR_HTTP2_PROTOCOL_ERROR error was being caused by my server (IIS) canceling the request because the throughput rate from my server fell below the minBytesPerSecond threshold.

    So for all you reading this right now, if you’re not using IIS, maybe there is a similar setting related to minimum throughput rate you can play with to see if it gets rid of the ERR_HTTP2_PROTOCOL_ERROR error.

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  29. In my case, the time on my computer (browser client) was out of date, synced it using settings in windows, and then the error got away

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  30. I had line breaks in my Content-Security-Policy in my nginx.conf that produced this error when used in an docker container running in Kube in GCP (serving angular but I doubt that matters).

    Putting them all back on the same line and the problem went away.

    A curl -v helped diagnose.

     http2 error: Invalid HTTP header field was received: frame type: 1, stream: 1, name: [content-security-policy], value: [script-src 'unsafe-inline' 'self....

    It was much easier to edit on separate lines but never again!

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  31. Just writing to help someone with the same scenario. I use .NET Core 6 API + Angular 13. The problem was with my JSON serializer options max depth. I increased it and the problem was fixed.

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  32. Our ASP.Net application was throwing the same error. Other applications on the same server using the same SSL certificate were running fine.

    Inexplicably, it turns our the error was due to the SQL Server Express database reaching it’s limit of 10GB. We found the error in the Windows error log.

    Clearing some tables and reducing the DB size solve the error!!

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  33. I also got the same issue and what I did was just simply go to Help > About Google Chrome and update the to the latest version.

    After the updating process done, this error will disappear and I can browse anything I want as usual again.

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  34. Just posting here to let people know that ERR_HTTP2_PROTOCOL_ERROR in Chrome can also be caused by an unexpected response to a CORS request.

    In our case, the OPTIONS request was successful, but the following PUT that should upload an image to our infrastructure was denied with a 410 (because of a missing configuration allowing uploads) resulting in Chrome issuing a ERR_HTTP2_PROTOCOL_ERROR.

    When checking in Firefox, the error message was much more helpful:

    Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://www.[...] (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 410.

    My recommendation would be to check an alternative browser in this case.

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  35. I experienced the same issue in C# NET Core 6. I was writing results to the body response with the method WriteAsync and returning with Task.CompletedTask

    Like below:

    await ctx.Response.WriteAsync("something to return");
    return Task.CompletedTask;

    And changed it to the code below:

     await ctx.Response.WriteAsync("something to return");
     return ctx.Response.CompleteAsync();

    And it works fine now.

    Apparently, you need to tell the Response object that you finished editing it.

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  36. My problem was that my access token was too large, making the header also too large, so I refactored its content to fix the error

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  37. In my case (HTTPS protocol, PHP) the reason was:

    wrong 404 header (

    header('404 Not found', true);

    instead of

    header($_SERVER['SERVER_PROTOCOL'].' 404 Not found', true);

    ) – legacy from previous web developer.

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  38. maybe HDD is fill fully.
    try clean.

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  39. I cleared the browser cache. It did not work.
    Then I flush the dns cache by ipconfig /flushdns. It work!

    Helpful link:

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  40. This issue can also occur when you have an application pool recycle (in IIS) while loading a page that takes a long time to load (e.g., it contains complex queries that take time to execute).

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  41. In my case net::ERR_HTTP2_PROTOCOL_ERROR 200 was caused by (AWS) load balancer that terminates idle connections after 60 seconds.

    If no data has been sent or received by the time that the idle timeout period elapses, the load balancer closes the connection. To ensure that lengthy operations such as file uploads have time to complete, send at least 1 byte of data before each idle timeout period elapses, and increase the length of the idle timeout period as needed.

    And terminated connection was a long polling endpoint, that sends no data if there is no events on the backend. More about this on this blog post which helped me a lot.

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  42. Just to add to the long list of seemingly arbitrary causes, here is mine:


    • Migrating a 32 bit classic ASP website running on Windows Server 2012 that does use the 32 bit MDB OleDB drivers to access an Access DB.
    • Migrating to a Windows Server 2022.
    • Trying to improve things and installing the 64 bit OleDB MDB drivers, changing the connection string from Microsoft.Jet.OLEDB.4.0 to Microsoft.ACE.OLEDB.12.0 then running the application in a 64 bit App Pool in IIS.

    This causes random ERR_HTTP2_PROTOCOL_ERROR errors because of the App Pool crashing.

    How to fix

    The fix was:

    • Uninstall the 64 bit MDB OleDB drivers.
    • Install the 32 bit MDB OleDB drivers.
    • Switch the App Pool to 32 bit again.

    I do hope I finally find the time to migrate all this to some modern ASP.NET Core, but for now this was the fastest fix.

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