Cross-language interop (go-js / js-go) #

This directory is the runnable cross-language example and conformance harness for capnweb-go. It exercises the Cap'n Web protocol in both directions against the reference TypeScript implementation (cloudflare/capnweb), proving the Go implementation is wire-compatible.

What it covers #

Server	Client	What it proves
TS	TS	Baseline — reference behavior
Go	TS	Go server encodes like the TS server (go → js)
TS	Go	Go client decodes like the TS client (js → go)

The service surface (defined identically in Go testService and TS TestService) covers: echo, add, greet, fail/failTyped, getChild (pass-by-reference), collect (streaming), plus the capnweb 0.8.0 features:

• makeBlob — a Blob round-trip, asserting MIME type + bytes survive the streaming pipe (["blob", type, ["readable", id]]).
• failWithProps — an Error carrying custom properties (code, detail) and a cause, asserting they propagate (["error", name, msg, null, props]).
• getInvalidDate — an invalid Date, asserting it serializes as ["date", null] and decodes back to an invalid/zero date.

Running locally #

You need Go, Node 22+, and a checkout of the reference implementation:

git clone https://github.com/cloudflare/capnweb /tmp/capnweb-ref
cd interop/ts && npm install && cd ../..

CAPNWEB_INTEROP=1 CAPNWEB_PATH=/tmp/capnweb-ref \
  go test -race -v -timeout 120s ./interop/...

Without CAPNWEB_INTEROP=1 the tests skip, so the suite is a no-op in environments that lack Node.

CI #

• ci.yml runs this suite on every PR against a pinned capnweb version (v0.8.0) for deterministic results.
• nightly.yml runs it against capnweb@latest as a drift alarm: a red nightly means upstream changed the wire protocol and the Go implementation needs to be re-aligned.