[browser] [wasm] Make response streaming opt-out #111680

campersau · 2025-01-21T21:48:59Z

This PR makes browser HTTP client to support streaming HTTP response by default. Until now, this feature was opt-in.

Because all evergreen browsers now support it.

This is compelling because it will make the GetFromJsonAsAsyncEnumerable streaming and lower memory consumption for large requests.

breaking change

This is a breaking change because the response.Content.ReadAsStreamAsync() is no longer MemoryStream but BrowserHttpReadStream which doesn't support synchronous operations like Stream.Read(Span<Byte>). If your code uses synchronous operations, you can disable the feature or copy the stream into MemoryStream yourself.

how to opt-out

If you need to disable it globally, you can use

<WasmEnableStreamingResponse>false</WasmEnableStreamingResponse> in your project file
set env variable DOTNET_WASM_ENABLE_STREAMING_RESPONSE

To disable it for individual request, you can use existing

request.Options.Set(new HttpRequestOptionsKey<bool>("WebAssemblyEnableStreamingResponse"), false);
or request.SetBrowserResponseStreamingEnabled(false) extension in Blazor project

Related to #77904
Fixes to #112442

lewing

I support this in principle. I'm concerned about how the breaking change will surface to people upgrading. My assumption is that it at the moment it will only show up at runtime?

campersau · 2025-01-22T07:18:52Z

Yes, it will only show up at runtime. Similar to Kestrels AllowSynchronousIO defaulting to false.
The main issue I will have with dotnet/runtime types is that ZipArchive does not support async #1541 and would throw.
An other workaround is to buffer the stream manually.

Could we add an app context switch to toggle this globally?

src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/BrowserHttpHandler.cs

dotnet-policy-service · 2025-01-22T14:11:52Z

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

pavelsavara · 2025-02-04T12:11:13Z

Could we add an app context switch to toggle this globally?

We could make it ILLink feature.
Similar to <InvariantGlobalization>true</InvariantGlobalization> for example.

I'm not sure if making the breaking change is worth it. Most people don't stream large data.

~~I would stick to existing behavior as default.~~ Ok, changed my mind

MihaZupan · 2025-02-04T12:25:44Z

FWIW this shouldn't be specific to just streaming large data.
A simple use case this affects can be streaming an AI chat response via GetFromJsonAsAsyncEnumerable or SseParser, where the preferred experience is that a partial response is displayed as soon as available.

lewing · 2025-02-04T16:39:45Z

The GetFromJsonAsAsyncEnumerable case is very compelling to me given that the overhead of processing large json blobs is particularly painful in both memory and responsiveness in browser with a single thread.

campersau · 2025-02-05T07:50:27Z

To me it looks like everyone supports this change. I guess it is still early to try it out in the previews then?

pavelsavara · 2025-02-05T08:29:49Z

@campersau I think we are missing the global opt-out linker feature. Are you willing to improve the PR ?

pavelsavara · 2025-02-27T08:58:59Z

I will work on adding global-opt out soon. @campersau I will take over this branch, ok ?

ZipArchive does not support async

BrowserHttpContent doesn't support sync API already.
So think this would not break anything new. Am I missing something ?

Yes, it will only show up at runtime.

If the developer didn't opt out, I can see few options:

A) at the start of request we can detect old browser and fail the request with some message hinting about possibilities how to opt out.
B) at the start of the runtime we can detect old browser and fail the runtime startup
C) we can detect old browser and resolve promise only once we received full response (no streaming) + issue warning to console

Thoughts ?

campersau · 2025-02-27T18:34:44Z

I will take over this branch, ok ?

Okay, I have tried to figure out how to do the linker opt out, but it is hard to find all the places which need to be updated.

BrowserHttpContent doesn't support sync API already.
So think this would not break anything new. Am I missing something ?

The BrowserHttpContent itself is only async but the Stream returned by BrowserHttpContent.ReadAsStreamAsync supports sync because it is just a MemoryStream:

runtime/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/BrowserHttpHandler.cs

Line 474 in bfc8814

return new MemoryStream(data, writable: false);

If the developer didn't opt out, I can see few options:
A) at the start of request we can detect old browser and fail the request with some message hinting about possibilities how to opt out.
B) at the start of the runtime we can detect old browser and fail the runtime startup
C) we can detect old browser and resolve promise only once we received full response (no streaming) + issue warning to console

I think all supported browsers support response streaming so I am not sure how you will detect it.
See #111680 (comment)

The true value here should be replaced by the global opt out value:
https://github.com/dotnet/runtime/pull/111680/files#diff-66ce677ded58c3a6a0639d321f4460bb0b2c4bcaeb3216ff3db4381937365bd8R317
Otherwise the developer can still opt out on a per request basis by setting WebAssemblyEnableStreamingResponse to false.

pavelsavara · 2025-02-27T20:51:33Z

Okay, I have tried to figure out how to do the linker opt out, but it is hard to find all the places which need to be updated.

Yes, no worries.

I think all supported browsers support response streaming

Use the same detection we have there already. To detect unsupported browser and proceed or fail in meaningful way.

pavelsavara · 2025-03-02T17:30:43Z

FYI @guardrex

guardrex · 2025-03-05T16:58:28Z

@pavelsavara ... Is the new opt-out approach ...

request.Options.Set(new HttpRequestOptionsKey<bool>("WebAssemblyEnableStreamingResponse"), false);

... landing at Preview 2?

- System.Net.Http.WasmEnableStreamingResponse linker feature - DOTNET_WASM_ENABLE_STREAMING_RESPONSE env variable - tests & docs

pavelsavara · 2025-03-07T18:06:33Z

... landing at Preview 2?

@guardrex probably Preview 3. I added some text in src/mono/wasm/features.md on this PR.

I also updated description on top of this PR

guardrex · 2025-03-07T18:12:28Z

Thanks @pavelsavara. I'll react to the updated description on the docs PR next week, and I'll ping for docs PR review later.

pavelsavara · 2025-03-10T19:35:59Z

This passed both FF and chrome tests.

pavelsavara · 2025-03-10T19:44:20Z

@campersau do you have any comments, I think this is ready

campersau · 2025-03-10T19:53:19Z

src/libraries/System.Net.Http/src/ILLink/ILLink.Substitutions.xml

@@ -4,4 +4,9 @@
      <method signature="System.Boolean IsGloballyEnabled()" body="stub" value="false" feature="System.Net.Http.EnableActivityPropagation" featurevalue="false" />
    </type>
  </assembly>
+  <assembly fullname="System.Net.Http" feature="System.Net.Http.WebAssemblyEnableStreamingResponse" featurevalue="false">
+    <type fullname="System.Net.Http.BrowserHttpController">
+      <method signature="System.Boolean get_FeatureEnableStreamingResponse()" body="stub" value="false" />


What exactly is value="false" / featurevalue="false"? The default value should be true or is this something else?

This means: if you set System.Net.Http.WebAssemblyEnableStreamingResponse to false then ILLink will stub the get_FeatureEnableStreamingResponse to return false instead of reading the config/env.

We don't want to also hardcode true do we ?

Is the behavior here the same in development as in publish?

We have something similar in Blazor routing and we had to do extra work for the development case
https://github.com/dotnet/aspnetcore/blob/main/src/Components/Components/src/Properties/ILLink.Substitutions.xml#L6-L8 for routing constraints, and it doesn't work in development unless you specifically set the AppContextSwitch manually

https://github.com/dotnet/aspnetcore/blob/f25dc7be397b496cc1c71f8720b2b7d67fb18649/src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostBuilder.cs#L98-L112

My understanding is that runtimeConfig.json stuff doesn't flow to wasm at the moment.

src/mono/wasm/features.md

campersau · 2025-03-10T20:01:13Z

src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/BrowserHttpInterop.cs

@@ -11,11 +11,26 @@ namespace System.Net.Http
 {
    internal static partial class BrowserHttpInterop
    {
+        private static bool? _SupportsStreamingRequest;
+        private static bool? _SupportsStreamingResponse;


Since this is now cached in .NET we don't need to cache it in JS anymore. Does not hurt though and might still be relevant for MT.

I removed it there, thanks. I believe that the webworker has the same feature set as UI thread.
If not, having static cache in C# side would be wrong.

Co-authored-by: campersau <buchholz.bastian@googlemail.com>

src/mono/wasm/features.md

pavelsavara · 2025-03-11T14:02:48Z

This is now dependent on #97449 because without it the Blazor dev loop would not reflect the AppContext feature switch.

pavelsavara · 2025-03-15T10:10:08Z

@lewing I think we should merge it into P3 anyway. Quite likely dev-loop users do have latest browsers.
So they would be only hit by the MemoryStream sync APIs problem and we would hear feedback sooner.

pavelsavara · 2025-03-17T16:38:55Z

/ba-g CI fails are unrelated

pavelsavara · 2025-03-18T08:10:18Z

Hmm, my bad, I overlooked HttpStreamingDisabledBy_WasmEnableStreamingResponse_InProject fail

#113628

[browser] [wasm] Make response streaming opt-out

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campersau requested review from lewing and pavelsavara as code owners January 21, 2025 21:48

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build-analysis bot mentioned this pull request Jan 22, 2025

[wasm] Out of memory exception in System.Xml.XmlWriterApiTests.TCFullEndElement tests #110090

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pavelsavara added arch-wasm WebAssembly architecture os-browser Browser variant of arch-wasm labels Jan 22, 2025

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lewing mentioned this pull request Feb 11, 2025

Make modern http streaming apis easily consumable in WebAssembly #112442

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guardrex mentioned this pull request Mar 3, 2025

Response streaming opt-out dotnet/AspNetCore.Docs#34870

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Blazor .NET 10 Tracking Issue dotnet/AspNetCore.Docs#34437

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Merge branch 'main' into responsestreamingoptin

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[wasm][AOT] emcc : error - received SIGKILL (-9) #89402

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- WebAssemblyEnableStreamingResponse msbuild property

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- System.Net.Http.WasmEnableStreamingResponse linker feature - DOTNET_WASM_ENABLE_STREAMING_RESPONSE env variable - tests & docs

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Merge branch 'main' into responsestreamingoptin

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- WebAssemblyEnableStreamingResponse msbuild property

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- System.Net.Http.WasmEnableStreamingResponse linker feature - DOTNET_WASM_ENABLE_STREAMING_RESPONSE env variable - tests & docs

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guardrex mentioned this pull request Mar 7, 2025

[Pre3] Response streaming default and opt-out dotnet/AspNetCore.Docs#34894

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Intermittent build failure in AfterSourceBuild: "Could not write state file" #76488

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Merge branch 'main' into responsestreamingoptin

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fix linker ?

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Update src/mono/wasm/features.md

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Co-authored-by: campersau <buchholz.bastian@googlemail.com>

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[browser] Support AppContext switches on runtime #97449

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[browser] [wasm] Make response streaming opt-out #111680

[browser] [wasm] Make response streaming opt-out #111680

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[browser] [wasm] Make response streaming opt-out #111680

[browser] [wasm] Make response streaming opt-out #111680

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breaking change

how to opt-out

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