Use `capnweb` native `ReadableStream` support for remote Media bindings by penalosa · Pull Request #12582 · cloudflare/workers-sdk

penalosa · 2026-02-17T14:30:23Z

Use capnweb's native ReadableStream support for remote Media and Dispatch Namespace bindings.

Build configuration

Add conditions: ["workerd", "worker", "browser"] to esbuild embed-worker plugins so capnweb resolves to its workerd entry point

Media bindings

Delete the intermediary binding.worker.ts — Media bindings now use remoteProxyClientWorker directly
Remove evaluateMediaBinding() / isSpecialCaseMediaBindingRequest() HTTP workaround from ProxyServerWorker.ts

Dispatch namespace bindings

Add dispatch-namespace-proxy.worker.ts — proxy client that creates capnweb stubs with dispatch options
Refactor dispatch-namespace.worker.ts to delegate to the proxy client via service binding

Shared utilities

Add makeRemoteProxyStub() for creating capnweb-backed Fetcher proxies
Add remoteProxyClientWorker() script override parameter for custom proxy workers
Add ProxyMetadata type and RemoteBindingEnv for consistent typing

Dependencies

Update capnweb to ^0.5.0 via pnpm catalog

Tests
- Tests included/updated
- Automated tests not possible - manual testing has been completed as follows:
- Additional testing not necessary because: existing tests cover this code, and should still work
Public documentation
- Cloudflare docs PR(s):
- Documentation not necessary because: Internal plumbing change, no user-facing API changes

changeset-bot · 2026-02-17T14:30:27Z

🦋 Changeset detected

Latest commit: 6d5ad38

The changes in this PR will be included in the next version bump.

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devin-ai-integration

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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claude · 2026-02-18T00:02:40Z

Claude finished @penalosa's task —— View job

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⚠️ Issues found

The changeset description is too minimal. According to the guidelines:

Bad Examples (avoid these)

"update dependency" - Which one? Why? Any user impact?

The current changeset says:

"Use capnweb's native ReadableStream support for remote Media and Dispatch Namespace bindings"

This needs more context:

What was the problem? (HTTP-based workaround was being used)
What changed? (Removed HTTP fallback, now uses capnweb's native support)
User impact? (Is this a performance improvement? Does it fix any bugs? Is it purely internal?)

Per the guidelines, aim for "more than one sentence but less than three paragraphs." A good changeset should explain the reason for the change and anything notable about the approach.

Suggested improvement:

---
"miniflare": patch
"wrangler": patch
---

Use capnweb's native ReadableStream support for remote Media and Dispatch Namespace bindings

Previously, remote Media bindings used an HTTP-based workaround to handle streaming data. With capnweb 0.5.0's native ReadableStream support, we've removed this intermediary HTTP layer and now communicate directly via RPC, simplifying the implementation and improving performance.

pkg-pr-new · 2026-02-18T00:07:11Z

create-cloudflare

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@cloudflare/kv-asset-handler

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miniflare

npm i https://pkg.pr.new/miniflare@12582

@cloudflare/pages-shared

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@cloudflare/unenv-preset

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@cloudflare/vite-plugin

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@cloudflare/vitest-pool-workers

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@cloudflare/workers-editor-shared

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@cloudflare/workers-utils

npm i https://pkg.pr.new/@cloudflare/workers-utils@12582

wrangler

npm i https://pkg.pr.new/wrangler@12582

commit: 6d5ad38

… bindings This PR updates miniflare to use capnweb's native ReadableStream support (via workerd entry point) for remote Media and Dispatch Namespace bindings. Changes: - Update capnweb to PR 139 (adds Headers/Request/Response + streams support) - Remove custom Media binding worker - use remote-proxy-client directly - Simplify dispatch-namespace to use service binding pattern (like Media) - Add makeRemoteProxyStub() helper for capnweb RPC + fetch interception - Configure esbuild with workerd conditions for capnweb workers The dispatch-namespace binding now uses JSRPC with promise pipelining, so `namespace.get('worker').fetch(request)` works without extra round-trips.

packages/miniflare/scripts/build.mjs

- Add optional workerScript param to remoteProxyClientWorker() - Use remoteProxyClientWorker() in dispatch-namespace plugin (consistency) - Fix protocol downgrade: https→wss, http→ws (was always using ws:)

The refactor into makeRemoteProxyStub dropped the bindingType → MF-Binding-Type forwarding that the AI RPC workaround in ProxyServerWorker depends on.

…b from user worker Move capnweb out of the dispatch namespace extension module (which runs in the user's isolate) into a dedicated proxy worker accessed via service binding. The extension is now a thin shim that delegates .get() calls. Also: simplify extraContext plumbing in remote-proxy-client, revert unrelated worker-ts fixture changes.

fixtures/worker-ts/src/index.ts

fixtures/worker-ts/wrangler.jsonc

packages/miniflare/src/plugins/dispatch-namespace/index.ts

packages/miniflare/src/workers/dispatch-namespace/dispatch-namespace-proxy.worker.ts

packages/miniflare/src/workers/shared/remote-proxy-client.worker.ts

packages/wrangler/tsup.config.ts

pnpm-workspace.yaml

…rker, update capnweb to 0.5.0

dario-piotrowicz

Nice! 😄 looks good to me 🙂

penalosa requested a review from a team as a code owner February 17, 2026 14:30

devin-ai-integration bot reviewed Feb 17, 2026

View reviewed changes

workers-devprod added this to workers-sdk Feb 18, 2026

github-project-automation bot moved this to Untriaged in workers-sdk Feb 18, 2026

penalosa marked this pull request as draft February 18, 2026 09:36

penalosa changed the title ~~[miniflare][wrangler] Use capnweb native ReadableStream support for remote Media bindings~~ Use capnweb native ReadableStream support for remote Media bindings Feb 18, 2026

penalosa force-pushed the penalosa/test-capnweb-streams branch 6 times, most recently from fc2e1a3 to 4d0a95b Compare February 19, 2026 00:03

penalosa force-pushed the penalosa/test-capnweb-streams branch from 4d0a95b to 87328d7 Compare February 19, 2026 09:46

penalosa commented Feb 19, 2026

View reviewed changes

packages/miniflare/scripts/build.mjs Outdated Show resolved Hide resolved

penalosa added 4 commits February 19, 2026 14:11

refactor(miniflare): clean up remote binding patterns

1aca4ea

- Add optional workerScript param to remoteProxyClientWorker() - Use remoteProxyClientWorker() in dispatch-namespace plugin (consistency) - Fix protocol downgrade: https→wss, http→ws (was always using ws:)

add test

6802bbf

fix(miniflare): restore bindingType forwarding in remote proxy client

fa045f5

The refactor into makeRemoteProxyStub dropped the bindingType → MF-Binding-Type forwarding that the AI RPC workaround in ProxyServerWorker depends on.

penalosa commented Feb 19, 2026

View reviewed changes

Address review feedback: simplify comments, reuse remoteProxyClientWo…

6d5ad38

…rker, update capnweb to 0.5.0

penalosa marked this pull request as ready for review February 19, 2026 18:45

dario-piotrowicz approved these changes Feb 19, 2026

View reviewed changes

github-project-automation bot moved this from Untriaged to Approved in workers-sdk Feb 19, 2026

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Use `capnweb` native `ReadableStream` support for remote Media bindings#12582

Use `capnweb` native `ReadableStream` support for remote Media bindings#12582
penalosa wants to merge 6 commits intomainfrom
penalosa/test-capnweb-streams

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penalosa commented Feb 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Build configuration

Media bindings

Dispatch namespace bindings

Shared utilities

Dependencies

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penalosa commented Feb 17, 2026 •

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