fix: treat CONNECT requests as the transport mechanism

[kettanaito]

• Fixes msw v3.0 - Invalid URL thrown in handler lookup for CONNECT requests when Node's NODE_USE_ENV_PROXY=1 is set #2795
• Requires Support tls.connect({ socket }) interceptors#807

Root cause

Root cause is in the interceptors, by design, and msw doesn't account for it.

1. Interceptors 0.45.5 intercepts at the socket level. The ClientRequest and fetch
   interceptors both feed off NodeHttpRequestSource, which parses raw HTTP off the
   socket. When a client goes through a proxy, the first exchange on the socket is
   CONNECT host:port, so that's the first request msw sees. In v2 the fetch
   interceptor patched fetch itself, so msw only saw the final GET with a full URL
   and the tunnel was invisible. That's the regression.
2. FetchRequest deliberately rewrites request.url to authority form for CONNECT.
   See node_modules/@mswjs/interceptors/lib/node/fetch-utils-Be80XVGM.js:384. The
   parser first builds http:///127.0.0.1:49284, then the constructor
   overrides the url getter to return just 127.0.0.1:49284. The source relies on
   this for tunnels, since a mocked CONNECT does new URL(http://${request.url}).
3. msw calls new URL(request.url) unguarded and a scheme-less authority throws
   ERR_INVALID_URL. Call sites hit for CONNECT:
   • src/utils/is-common-asset-request.ts (no handlers registered, the
     unhandled-frame path)
   • src/http/http-handler.ts:125 in parse (any http handler registered)
   • src/core/experimental/frames/http-frame.ts:127 in getUnhandledMessage
   • src/core/utils/logging/serialize-request.ts:18 and get-request-cookies.ts:32
     would follow.
4. The throw becomes a 500. In http-frame.ts:169 the lookup error is logged and
   errorWith(lookupError) is called, which the interceptor turns into a 500 on the
   socket. Undici then fails with Proxy response (500) !== 200 when HTTP Tunneling.

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📝 Walkthrough

Walkthrough

HTTP handler lookup now excludes CONNECT requests. Unmatched CONNECT requests pass through without unhandled-frame handling. Node tests cover CONNECT lifecycle events and proxy requests. The Vite HMR test checks network state before an update and waits for a mocked response.

Changes

CONNECT Passthrough

Layer / File(s)	Summary
Exclude CONNECT from HTTP handler matching package.json, src/http/http-handler.ts, src/http/http-handler.test.ts	HttpHandler.parse returns a non-match for CONNECT requests. A predicate test checks this behavior. The @mswjs/interceptors dependency range changes to ^0.45.6.
Pass unmatched CONNECT requests through src/core/experimental/frames/http-frame.ts, src/core/experimental/frames/http-frame.test.ts, test/msw-api/setup-server/scenarios/request-connect.node.test.ts	Unmatched CONNECT requests emit request:end and pass through without unhandled-frame handling. Tests cover lifecycle events, handler matching, callbacks, and error and warn strategies.
Test CONNECT requests through an HTTP proxy test/support/proxy-server.ts, test/regressions/2795-connect-env-proxy.node.test.ts	A test proxy forwards CONNECT tunnels and supports GET requests through them. Regression tests check origin and mocked responses through the proxy.

Vite HMR Test Timing

Layer / File(s)	Summary
Check network state and wait for the mocked response src/vite/plugin.test.ts	The HMR test checks that the network is disabled before an update. It polls for up to 10 seconds for the resource response to become mocked.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to bbfb5

The selected change adjusts test timing and network-state checks for the Vite HMR test. No actionable merge-blocking risk remains in the supplied context.

Architecture Summary

Architecture risk: 🔵 Low · up to e2284

The change affects 3 systems.

Changed systems: src, test, package.json

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — src (service) was modified; 5 changed files map to changed impact.
• observed — test (service) was modified; 3 changed files map to changed impact.
• observed — package.json (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in package.json: The @mswjs/interceptors dependency range changed from ^0.45.5 to ^0.45.6.
• observed — Modified behavior in src/core/experimental/frames/http-frame.test.ts: The test file now imports FetchRequest for constructing a CONNECT request.
• observed — Modified behavior in src/core/experimental/frames/http-frame.test.ts: Adds a test using a FetchRequest with method CONNECT and an http.all('*') handler. It expects no handler match (null), passthrough without response, error, or unhandled-frame callback, and only start/end request events. The test comment notes that http.connect() support and precedence remain to be revisited.
• observed — Modified behavior in src/core/experimental/frames/http-frame.ts: Imports isStringEqual for the CONNECT method comparison.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The CONNECT handling code, proxy support, dependency update, and related tests stay within issue #2795. The changes to src/vite/plugin.test.ts modify browser HMR network-state tracking and polling…	Remove the unrelated src/vite/plugin.test.ts changes, or provide a concrete requirement from issue #2795 that they implement.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: treating CONNECT requests as a transport mechanism. It is concise and directly related to the proxy tunnel fix.
Description check	✅ Passed	The description explains the CONNECT request failure, the interceptor behavior, the ERR_INVALID_URL root cause, and the related issue and dependency. It is directly related to the changeset.
Linked Issues check	✅ Passed	Issue #2795 requires CONNECT requests to avoid ERR_INVALID_URL and unhandled handler-lookup failures. HttpHandler.parse rejects CONNECT before URL construction. HttpNetworkFrame.resolve pass…
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 8 files.

Full details: Out of Scope Changes check

Explanation

The CONNECT handling code, proxy support, dependency update, and related tests stay within issue #2795. The changes to src/vite/plugin.test.ts modify browser HMR network-state tracking and polling behavior. The available evidence does not connect these changes to proxy CONNECT handling.

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_{A rabbit watched the tunnel pass,
While CONNECT slipped through the glass.
The handlers waited for a GET,
Then served the mock without a fret.
HMR woke when the network came,
And bunnies cheered the passing frame.}

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commit: 4b673cc

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Actionable comments posted: 1

🧹 Nitpick comments (1)

test/msw-api/setup-server/scenarios/request-connect.node.test.ts (1)

29-53: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Assert the tunneled response body in each scenario.

proxiedGet sends a CONNECT, then sends the GET over the tunnel. The fixture returns original, while the registered GET handler returns mocked. Both responses have status 200, so the current assertions can pass if the tunneled GET bypasses MSW. Add the body assertion to the error, warn, custom callback, and lifecycle tests.

Suggested fix

-  const { response } = await proxiedGet({
+  const { response, responseText } = await proxiedGet({
     proxyUrl: proxyServer.url,
     targetUrl,
   })

   expect(response.statusCode).toBe(200)
+  expect(responseText).toBe('mocked')

Apply the same change to the other three tests.

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Review comment at
@test/msw-api/setup-server/scenarios/request-connect.node.test.ts around lines
29 - 53:
Update the tests for the error, warn, custom callback, and lifecycle scenarios
using proxiedGet to capture responseText and assert it equals the mocked GET
response, in addition to the existing status assertion.

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Inline comments:
Review comments at @test/support/proxy-server.ts:
- Around line 19-31: Add paired error handlers for the clientSocket and
targetSocket in the proxy connection setup so an error on either socket destroys
the other, preventing unhandled socket errors.

---

Nitpick comments:
Review comments at
@test/msw-api/setup-server/scenarios/request-connect.node.test.ts:
- Around line 29-53: Update the tests for the error, warn, custom callback, and
lifecycle scenarios using proxiedGet to capture responseText and assert it
equals the mocked GET response, in addition to the existing status assertion.

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Inline comments:
Review comments at @src/vite/plugin.test.ts:
- Around line 457-459: Clear the before-update marker after the first update’s
assertion and before the second update sent through
server.environments.client.hot, so the later assertion can only pass if the
listener runs for that update.

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@​mswjs/​interceptors@​0.45.5 ⏵ 0.45.6	+1		+1	+1

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[kettanaito]

Released: v3.0.1 🎉

This has been released in v3.0.1.

• 📄 Release notes
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