Meaning of "The server returned an invalid or unrecognized response" in HttpClient

c# .net http .net-core

15,521

You can reproduce this 100% of the time when calling an https only endpoint using an http schemed call. So for instance calling an API at:

https://www.mysecureapi.com

using

http://www.mysecureapi.com

15,521

Mark Amery

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Updated on June 07, 2022

Comments

Mark Amery about 2 years

When awaiting an HttpClient.PostAsync response, I sometimes see an error stating "The server returned an invalid or unrecognized response":

System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.Http.WinHttpException: The server returned an invalid or unrecognized response
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at System.Net.Http.WinHttpHandler.<StartRequest>d__105.MoveNext()
   --- End of inner exception stack trace ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at System.Net.Http.HttpClient.<FinishSendAsync>d__58.MoveNext()

That's a pretty cryptic error; I suppose I can conceive of what an "invalid" response might possibly be (i.e. a syntactically-invalid HTTP response, like one that jumps straight into headers without a status line), but what on earth is an "unrecognized" response to a HTTP request? The message seems like nonsense.

What circumstances can actually trigger this error, under the hood?

stuartd almost 7 years

You could log all your responses until you get the error?
TnTinMn almost 7 years

This may provide some insight. https://github.com/dotnet/corefx/issues/14897.

Mark Amery over 5 years

That seems unlikely. APIs typically return a 401 or 403 response in this case, which is still a valid HTTP response.
crthompson almost 5 years

This was exactly my error. I had inadvertently switched to https, but had http in the config.
crthompson almost 5 years

@MarkAmery that is exactly what happened to me that caused this error. Calling http instead of https, you DONT get a valid http response.
Mark Amery almost 5 years

@paqogomez But this answer has nothing to do with HTTP vs HTTPS.
crthompson almost 5 years

I think it does. OP states that doing an http request without token (which would make it https if it was with token). Trying to call a "secured" method is another indicator. While yes, I can see some ambiguity there, I think they are talking about http vs https
Mark Amery almost 5 years

@paqogomez The TLS protocol used to encrypt HTTPS connections doesn't involve anything commonly referred to as a "token" as far as I know. The normal meaning of "authorization token" is this: en.wikipedia.org/wiki/Access_token - a token that identifies a login session or a user, usually sent in a cookie or a custom HTTP header. Unrelated to HTTPS.
user3502626 almost 5 years

I am getting the same error. I changed Https to Http but I'm still getting the same error.
rism almost 5 years

@user3502626 And? The question was not about how to fix the error - it asked how to reproduce it.
Nikunj Kakadiya about 4 years

It is working for me... Thank you thank you so much