fix: retry DialContext on conn-fatal dial to replace stale transport - #15
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When the shared TLS+H2 connection is reset (e.g. by DPI), getTransport can hand back a pooled transport whose conn is dead but not yet marked closed. openTunnel then fails conn-fatally and retires it, but DialContext surfaced that as a hard dial failure even though the next getTransport would create a fresh, working transport. Wrap the getTransport+openTunnel pair in a bounded retry loop: on a conn-fatal openTunnel error (which retires the dead transport), redial on a fresh one, up to maxDialAttempts. Non-conn-fatal errors (caller cancellation, non-200 CONNECT) break immediately. Also make openTunnel's closed-transport guard wrap net.ErrClosed so a transport retired concurrently between getTransport and openTunnel reads as conn-fatal and is retried rather than hard-failing.
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ChangesDial retry flow
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟡 Moderate · up to The new retry behavior can start another dial after the caller has canceled the request, causing unnecessary network work and potentially returning the wrong error instead of context.Canceled. The PR should add a context check before each retry and verify that cancellation prevents additional attempts. Sequence Diagram(s)sequenceDiagram
participant Caller
participant DialContext
participant TransportPool
participant openTunnel
Caller->>DialContext: dial destination
DialContext->>TransportPool: acquire transport
TransportPool-->>DialContext: return transport
DialContext->>openTunnel: open tunnel
openTunnel-->>DialContext: connection-fatal error
DialContext->>TransportPool: acquire fresh transport
DialContext->>openTunnel: retry tunnel
openTunnel-->>DialContext: return connection or final error
DialContext-->>Caller: return result
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✅ Passed checks (4 passed)
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Inline comments:
In `@client.go`:
- Around line 72-91: In client.go lines 72-91, update the retry loop around
getTransport and openTunnel to check ctx.Err() at the start of every attempt and
return the cancellation error before acquiring another transport. In
samizdat_test.go lines 818-835, use a cancelable DialContext context, cancel it
before the first RoundTrip returns net.ErrClosed, and assert createCount remains
1 with the returned error matching context.Canceled.
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client.goh2transport.gosamizdat_test.go
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Pull request overview
This pull request improves client dial reliability when a pooled TLS+HTTP/2 transport becomes stale (e.g., after a network reset) by retrying DialContext on connection-fatal tunnel establishment failures so a fresh transport can be created and used instead of surfacing an immediate hard failure.
Changes:
- Add a bounded retry loop in
Client.DialContextthat retriesgetTransport+openTunnelonconnFatalerrors (up tomaxDialAttempts). - Make
h2Transport.openTunnelreport “transport closed” asnet.ErrClosed-wrapped so it is classified asconnFataland triggers a retry. - Add tests covering retry behavior, max-attempts behavior, and “closed transport” conn-fatal classification.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
client.go |
Retries DialContext on conn-fatal tunnel failures with a bounded attempt cap. |
h2transport.go |
Wraps the closed-transport guard with net.ErrClosed so it becomes retryable/conn-fatal. |
samizdat_test.go |
Adds unit tests validating retry/no-retry behavior and conn-fatal classification. |
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A conn-fatal openTunnel error can race with caller cancellation, so the retry loop could start another attempt on an already-abandoned dial and return a wrapped transport error instead of the cancellation. Check ctx.Err() at the start of each attempt and return the context error directly.
Problem
When the shared TLS+H2 connection to a Samizdat server is reset (e.g. by DPI on an adversarial ISP),
connPool.getTransportcan hand back a pooled transport whose underlying conn is dead but not yet marked closed.openTunnelthen fails with a conn-fatal error (net.ErrClosedetc.) and retires that transport — butClient.DialContextsurfaced this as a hard dial failure, even though the very nextgetTransportwould create a fresh, working transport.The observed signature was sustained bursts of
use of closed network connectiondial failures against otherwise-usable servers, each needlessly failing a dial that an immediate redial would complete.Fix
getTransport+openTunnelpair inDialContextin a bounded retry loop. On a conn-fatalopenTunnelerror (which has already retired the dead transport), redial on a fresh transport, up tomaxDialAttempts(3). Non-conn-fatal errors — caller cancellation, a non-200 CONNECT response — break immediately.openTunnel's closed-transport guard wrapnet.ErrClosedinstead of a bare string, so a transport retired concurrently in the window betweengetTransportandopenTunnelreads as conn-fatal and is retried rather than hard-failing.Tests
TestDialContextRetriesAfterConnFatal— dead transport retired, fresh one dialed.TestDialContextNoRetryOnCallerCancel— caller cancellation does not redial.TestDialContextGivesUpAfterMaxAttempts— gives up after the bound.TestOpenTunnelOnClosedTransportIsConnFatal— the closed-transport guard is conn-fatal.go build ./...andgo test ./... -racepass.Not addressed
This targets conn-fatal dial-time failures only. Mid-stream RST/stall churn and domain-front bootstrap failures are separate and unchanged.
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