Reason why JsonContent (From CoreFx) method TryComputeLength is False

[moisoiu]

Hello,

I'm having a hard time understanding why TryComputeLength from JsonContent is on false and length is 0.

Scenario.
The application that I'm working on uses PostAsJsonAsync from System.Net.Http.Json.HttpClientJsonExtensions and I'm using it to call different backends.

If I run locally, I have no issue, I receive an answer from backend on which I make the request. But as soon as I deployed in Azure App Service, it returns me bad request. And I don't understand why

The reason why I'm asking is because If I create a mockup JsonContent and change the TryComputeLength from false to true and set the length manually it works

The only solution that I found is to replace JsonContent with ByteArrayContent

Also on the Bad Request it returns me a header Transfer-Encoding: chunked

So anyone any idea, because I don't think is a bug in the JsonContent but in the same time I don't understand why it works locally but not on Azure App Service

[huoyaoyuan]

TryComputeLength means if the length can be given immediately. Serializing arbitrary content may consume time that's sensitive for control flow.

You can use LoadIntoBufferAsync() to do the serialization. It will store the result internally, then the length can be get immediately. See my code here.

It also surprises me when I was debugging my code, because inspecting the json content in debugger will make the code execute successfully.

Many code supposes chunked encoding is supported everywhere, because it's a part of HTTP spec. So does HttpClient.

[moisoiu]

You're right, after further investigation we found the cause. It seems like this was a Firewall configuration where for some reason is not allowing this type of requests.

Thanks for the tips with LoadIntoBufferAsync !

[stuartclode]

Great catch. Thanks for figuring this out.