"body stream already read" error due to broken blazor wasm fallback

[kg]

Right now if a streaming compile of the blazor wasm binary fails, we fall into a fallback path that won't actually work. It produces this error:

TypeError: Failed to execute 'arrayBuffer' on 'Response': body stream already read

This is because the first compile attempt already consumed the body of the response, and it can't be consumed a second time. The fix is to issue a second fetch before attempting to compile again. We would want to do that in the fallback path above here:

aspnetcore/src/Components/Web.JS/src/Platform/Mono/MonoPlatform.ts

Line 646 in 98641b0

const arrayBuffer = await wasmResource.response.then(r => r.arrayBuffer());

We also currently just try to do a streaming compile, but the most common failure case is detectable without trying to compile - if the content-type of the response is not application/wasm the streaming compile will always fail, so we should probe for that (via response.headers.get("Content-Type")) and if it doesn't match we should just immediately jump to the fallback. This would eliminate the need for a 2nd fetch.

(The second fetch shouldn't be a performance issue anyway, it should hit the browser cache.)

cc @radical

[radical]

An issue where this manifested - #40528

[radical]

cc @pranavkm

[javiercn]

Seems that the underlying issue is the OOM happening.

I'm closing this issue in favor of #40547

[TanayParikh]

Re-opening as dotnet/runtime#95971 is more related to changing the error message.

[ghost]

Thanks for contacting us.

We're moving this issue to the .NET 7 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[CoryKoehler]

@danroth27 @SteveSandersonMS
Hello, I put in an issue similar and closed it since this one seems to be the one where everything is tracked regarding this.
I don't think this can be pushed to .Net7. I am having customers complain currently on this. Depending on device (both Android and IOS are affected)

This to me seems huge and would make my clients rethink any investment in Blazor.
An existing production site that is blazor wasm hosted that is having this issue is boatsforsale.com and replicate this issue with enough attempts on smaller devices. The site will display just a loading spinner forever and in the console you'll see

Is there any way this could be looked into for an earlier release than next nov?
@chassq

[SteveSandersonMS]

@CoryKoehler I suspect this issue isn't your actual problem, and that dotnet/runtime#95971 is. We have an ongoing discussion with the runtime team and will post updates there.

[CoryKoehler]

@SteveSandersonMS thank you so much. I have been trying to keep track of all the related issues across repositories that seem to be related to this. That is helpful to start getting an idea of where you all are at.

Would it be helpful or noise for me to put my above comment into that issue?

[TanayParikh]

I'm going to close this out in favor of #42055.