[wasi] Enable Brotli and Zstandard on CoreCLR WASI by lewing · Pull Request #136257 · dotnet/runtime

lewing · 2026-10-21T23:39:42Z

Enables System.IO.Compression.Brotli and Zstandard (ZstandardStream and related types) on CoreCLR WASI. Browser is unchanged and still excludes both.

Why

Both codecs were excluded on all of wasm because browser leaves them out for download size. WASI apps always relink the native runtime with a P/Invoke table generated from the app's trimmed assemblies, so a codec's native code is only linked into apps that use it.

Measured on relinked, trimmed sample apps (Release, wasm-tools strip -a):

App	Host size	Delta	gzip -9 delta
GZip only	5,521,734	—	—
GZip + BrotliStream	6,355,085	+833 KB	+316 KB
GZip + ZstandardStream	6,028,091	+506 KB	+121 KB

The GZip-only host contains no Brotli* or ZSTD_* symbols.

Changes

Native/build: brotli build, includes and entry points are now gated on !browser instead of !wasm. The brotli libs are linked in the CoreCLR WASI app relink, the NativeAOT WASI link and the Mono WASI runtime link; libzstd is linked unconditionally in the CoreCLR relink. Duplicate libs.native copies are excluded from the WASI CoreCLR runtime pack, as for libz.a.
Managed: System.IO.Compression.Brotli gains a -wasi TFM. System.IO.Compression compiles the real Zstandard implementation for wasi. wasi is removed from UnsupportedOSPlatform on the Brotli assembly, the Zstandard types, and BrotliCompressedContent/ZstandardCompressedContent (src and ref).
Call helpers: src/coreclr/vm/wasm/wasi/callhelpers-pinvoke.cpp is regenerated in the commit that adds each codec's P/Invokes (Compression.Native table: 9 → 21 → 51 entries).
Tests: the Brotli tests now target WASI, and CompressedContentTest.NonBrowser.cs is compiled for WASI.

Validation

CoreCLR WASI, Release, wasmtime 49.0.1:

System.IO.Compression.Brotli.Tests: 259 run, 251 passed, 0 failed, 8 skipped (existing IsMultithreadingSupported conditions).
System.Net.Http.Functional.Tests -class CompressedContentTest: 48 run, 47 passed, 1 skipped (existing 32-bit zstd SmallestSize case). This covers the br and zstd round-trips.
System.IO.Compression.Tests built for wasi locally: all 316 Zstandard tests passed, 10 skipped on capability conditions.
ApiCompat outer builds of Brotli, System.IO.Compression and System.Net.Http are clean.
The Mono WASI runtime (mono.runtime+mono.corelib+mono.wasiruntime) builds and links.
Not run locally: a NativeAOT WASI app link that uses Brotli.

Known gaps

There's no dedicated Zstandard test suite on WASI yet. System.IO.Compression.Tests doesn't target wasi because its WinZip AES and encrypted-zip tests fail there (cryptography isn't supported on WASI) and need gating first.
SocketsHttpHandler decompression of br/zstd on WASI is covered by [wasi] Enable SocketsHttpHandler and WebSockets #136234.

Related: #91279 (Brotli on browser; not addressed here)

Note

This PR description was generated with GitHub Copilot.

Brotli was excluded on all of wasm because browser omits it for download size. WASI apps relink the native runtime with a P/Invoke table generated from the app's trimmed assemblies, so the Brotli static libraries are only pulled in when the app actually uses them. - Gate the brotli build/includes/entry points on !browser instead of !wasm. - Link libbrotlienc/libbrotlidec/libbrotlicommon in the CoreCLR WASI app relink, the NativeAOT WASI link, and the Mono WASI runtime link. - Exclude the duplicate libs.native brotli copies from the WASI CoreCLR runtime pack, matching libSystem.IO.Compression.Native.a and libz.a. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Add the wasi target framework so WASI gets the real implementation instead of the PlatformNotSupported assembly, and drop wasi from the unsupported platforms of System.IO.Compression.Brotli and BrotliCompressedContent. Regenerate the WASI call helpers for the new Brotli P/Invokes: ./build.sh clr+libs+packs -os wasi -c Release -rf CoreCLR src/coreclr/vm/wasm/generate-coreclr-helpers.sh -c Release --target-os wasi Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

libzstd.a is already built for WASI and linked by the CoreCLR WASI app relink, but the managed Zstandard types were PlatformNotSupported stubs there. Compile the real implementation for wasi, expose the ZSTD entry points on !browser, and drop wasi from the unsupported platforms of the Zstandard types and ZstandardCompressedContent. The regenerated WASI call helpers now always reference libzstd, so link it unconditionally in the CoreCLR WASI relink and add it to the Mono WASI runtime link. Regenerated with: ./build.sh clr+libs+packs -os wasi -c Release -rf CoreCLR src/coreclr/vm/wasm/generate-coreclr-helpers.sh -c Release --target-os wasi Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

azure-pipelines · 2026-10-21T23:40:36Z

Azure Pipelines: Successfully started running 5 pipeline(s). 11 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

dotnet-policy-service · 2026-10-21T23:41:10Z

Tagging subscribers to this area: @karelz, @dotnet/area-system-io-compression
See info in area-owners.md if you want to be subscribed.

dotnet-policy-service · 2026-10-21T23:41:52Z

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

azure-pipelines · 2026-10-22T14:26:12Z

No pipelines are associated with this pull request.

azure-pipelines · 2026-10-22T14:26:27Z

No pipelines are associated with this pull request.

lewing · 2026-10-22T14:26:44Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2026-10-22T14:26:58Z

Azure Pipelines: Successfully started running 1 pipeline(s).

pavelsavara · 2026-10-23T10:57:35Z

Does src\native\corehost\wasihost need to link new stuff too ?

- Keep the libs.native compression archives in the NativeAOT WASI runtime pack: NativeAOT packs take RuntimeFiles from aotsdk rather than sharedFramework, so the WASI CoreCLR duplicate exclusion dropped them. - Update the System.IO.Compression README: Zstandard is now only unsupported on browser. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

lewing · 2026-10-23T16:22:02Z

@pavelsavara No changes are needed in wasihost itself. src/native/corehost/wasihost only builds the static archive libWasiHost.a and doesn't link any runtime libraries. Those are supplied when each app is relinked in src/mono/wasi/build/WasiApp.CoreCLR.targets, which pulls in libWasiHost.a whole-archive together with the runtime-pack static libs. This PR adds libbrotlienc.a, libbrotlidec.a and libbrotlicommon.a to that link and makes libzstd.a unconditional. The in-tree corerun gets brotli through the PUBLIC link of System.IO.Compression.Native-Static.

Note

This reply was generated with GitHub Copilot.

Brotli and Zstandard now work on WASI (dotnet#136257). The decompression test servers disposed compression streams synchronously over the connection, which WASI doesn't support, and the Brotli buffer-limit test's write loop never yielded to a single-threaded client. The new Alt-Svc test needs TLS. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

lewing and others added 5 commits October 21, 2026 18:38

[wasi] Run System.IO.Compression.Brotli tests on WASI

e932067

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

[wasi] Run Brotli/Zstandard CompressedContent tests on WASI

be20929

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions Bot added the area-System.IO.Compression label Oct 21, 2026

dotnet-policy-service Bot assigned lewing Oct 21, 2026

lewing added arch-wasm WebAssembly architecture os-wasi Related to WASI variant of arch-wasm labels Oct 21, 2026

This was referenced Oct 22, 2026

[browser] Wasm.Build.Tests timeout - Timed out after 10s waiting for 'WASM EXIT' #116697

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Crash: access violation in coreclr!PgoManager::getPgoInstrumentationResults during tier-1 background JIT (Windows x86) #134695

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lewing marked this pull request as ready for review October 22, 2026 14:26

lewing requested review from MichalStrehovsky, akoeplinger, maraf and pavelsavara as code owners October 22, 2026 14:26

maraf reviewed Oct 23, 2026

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Comment thread eng/liveBuilds.targets

Comment thread src/libraries/System.IO.Compression/src/System.IO.Compression.csproj

maraf approved these changes Oct 23, 2026

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This was referenced Oct 23, 2026

Checkout failure: "Git fetch failed with exit code 128" dotnet/arcade#9009

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Unable to checkout dotnet/dnceng#4115

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build-analysis Bot mentioned this pull request Oct 23, 2026

[ci-scan] Test failure: System.Numerics.Tensors.Tests.TensorTests.TensorValueReductionsPreserveScalarOrder #136367

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lewing enabled auto-merge (squash) October 23, 2026 20:38

lewing merged commit 6f1e2a8 into dotnet:main Oct 23, 2026
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dotnet-maestro Bot mentioned this pull request Oct 24, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#10436

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[wasi] Enable Brotli and Zstandard on CoreCLR WASI - #136257

[wasi] Enable Brotli and Zstandard on CoreCLR WASI#136257
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