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: 712e2eb

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

devin-ai-integration

✅ Devin Review: No Issues Found

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

View in Devin Review to see 4 additional findings.

claude · 2026-02-18T00:02:40Z

Claude finished @penalosa's task —— View job

Changeset Review

⚠️ Issues found

The changeset .changeset/capnweb-streams-media-bindings.md appears to be marked as a patch for an internal refactor with no user-facing changes. According to .changeset/README.md:

When a Changeset is NOT Required

Changes that are purely internal refactoring with no user-facing impact

Based on the PR description and the review discussion between @penalosa and @petebacondarwin, this is described as "mostly just an internal refactoring" with the note that "Previously we 'faked' streams with Media Bindings over fetch, but now they will work properly."

Recommendation: If this is purely internal refactoring with no user-facing impact, the changeset should be removed entirely and the PR should be labeled with no-changeset-required. However, if there is a subtle user-facing improvement (streams now work properly for JSRPC calls to remote binding services), then the changeset should stay but the description should be clearer about what the actual user-facing benefit is.

The current description "Internal refactor to use capnweb's native ReadableStream support to power remote Media and Dispatch Namespace bindings" reads as purely internal with no user impact, which contradicts having a changeset at all.

pkg-pr-new · 2026-02-18T00:07:11Z

create-cloudflare

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@cloudflare/kv-asset-handler

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miniflare

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@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

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wrangler

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

commit: 712e2eb

packages/miniflare/scripts/build.mjs

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

dario-piotrowicz

Nice! 😄 looks good to me 🙂

petebacondarwin · 2026-02-20T08:52:01Z

.changeset/capnweb-streams-media-bindings.md

+"wrangler": patch
+---
+
+Use capnweb's native ReadableStream support for remote Media and Dispatch Namespace bindings


Is there any user facing change here? Or is this PR more of an internal refactoring?

This is mostly just an internal refactoring. Previously we "faked" streams with Media Bindings over fetch, but now they will work properly. As a consequence, any other JSRPC calls to a remote bings service binding that returns a stream will now also work. I suppose I could remove the changeset? What do you think?

… 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.

- 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.

…rker, update capnweb to 0.5.0

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

devin-ai-integration bot reviewed Feb 17, 2026

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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 7 times, most recently 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 commented Feb 19, 2026

View reviewed changes

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

dario-piotrowicz approved these changes Feb 19, 2026

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

petebacondarwin reviewed Feb 20, 2026

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petebacondarwin approved these changes Feb 20, 2026

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penalosa added 7 commits February 20, 2026 13:38

refactor(miniflare): clean up remote binding patterns

a6af778

- 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

68b6af2

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

05adc10

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

Address review feedback: simplify comments, reuse remoteProxyClientWo…

f640c47

…rker, update capnweb to 0.5.0

Update capnweb-streams-media-bindings.md

712e2eb

penalosa force-pushed the penalosa/test-capnweb-streams branch from d3969c4 to 712e2eb Compare February 20, 2026 13:38

penalosa merged commit c2ed7c2 into main Feb 23, 2026
39 of 42 checks passed

penalosa deleted the penalosa/test-capnweb-streams branch February 23, 2026 14:22

github-project-automation bot moved this from Approved to Done in workers-sdk Feb 23, 2026

workers-devprod mentioned this pull request Feb 23, 2026

Version Packages #12612

Merged

petebacondarwin mentioned this pull request Feb 23, 2026

fix: add maxRetries to recursive directory removal for Windows EBUSY #12629

Merged

5 tasks

penalosa mentioned this pull request Mar 19, 2026

Service binding RPC methods do not work with Response, ReadableStream when remote: true #11114

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Build configuration

Media bindings

Dispatch namespace bindings

Shared utilities

Dependencies

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