phsl / new-api

fix(relay): bound the wait for upstream response headers (fixes unbounded heap growth → OOM) (#6949)

* fix(relay): bound the wait for upstream response headers (fixes unbounded heap growth)

The relay transport sets a dial timeout, a TLS handshake timeout and an expect-continue
timeout, but nothing bounds how long it waits for the upstream *response headers* after
the request has been written. An upstream that accepts the connection and then never
answers -- without sending FIN/RST, which is what happens when a NAT/firewall silently
drops the flow or the provider hangs -- parks the goroutine in
net/http.(*persistConn).roundTrip forever.

That goroutine keeps the whole request alive, which in practice means three copies of the
request body stay reachable for the lifetime of the process: the raw bytes from
io.ReadAll in CreateBodyStorageFromReader, the decoded messages held as json.RawMessage,
and the re-marshalled upstream body from common.Marshal. BodyStorageCleanup cannot help
here: it runs after c.Next() returns, and for these requests c.Next() never returns.

Measured on v1.0.0-rc.23 in production (see #6947 for the full evidence):

  - 23 goroutines stuck in persistConn.roundTrip on a single 40h-old instance,
    blocked between 353 and 1894 minutes (5.9h to 31.5h)
  - 96.9% of the live heap, sampled after a forced GC, attributable to those three
    body copies (HeapAlloc 892 MiB surviving three GC cycles; HeapObjects dropping
    30x while bytes dropped only 25%)
  - the live floor grows with uptime: 33.7 MiB at 0.1h, 89.2 at 13.8h, 510.0 at 40.1h,
    955.2 at 146.8h, OOMKilled at 172.9h -- same image, same config, same load

Doubling the memory limit and adding GOMEMLIMIT only moved the OOM from 132h to 172.9h.

RELAY_TIMEOUT (http.Client.Timeout) cannot be used for this: it covers the whole response
read and would cut legitimate long streaming calls, which is why it defaults to 0.
ResponseHeaderTimeout only bounds the wait for the headers; streaming after they arrive is
unaffected.

The default is deliberately generous. Non-streaming upstreams usually send the response
headers only once generation has finished, so the value has to leave room for a long
completion. 1800s is 12x shorter than the shortest hang observed here while leaving
several times the headroom a normal non-streaming request needs; 0 restores the previous
unbounded behaviour.

The assignment goes next to the other transport.* lines rather than inside the else
branch: newRelayHTTPTransport() normally takes the http.DefaultTransport.Clone() path,
and DefaultTransport does not set ResponseHeaderTimeout either.

This repo already sets ResponseHeaderTimeout on its other outbound transports
(controller/model_sync.go, controller/ratio_sync.go); the relay path appears to have
been missed.

Refs #6947. Likely also the root cause of #6731, which reported the same symptom
(production OOM on /v1/responses after ~64h) but was closed for template reasons.

* review: clamp overflowing timeout values and switch the test to testify

Addresses the two CodeRabbit findings on this PR.

Overflow (common/init.go:113): a RELAY_RESPONSE_HEADER_TIMEOUT beyond ~9.2e9 seconds
overflows time.Duration and can wrap into a *tiny positive* timeout, which would cut
every relay request instead of only the stuck ones. The value is now clamped before the
conversion, with regression tests for both the negative and the overflowing input.

I did not add fail-on-startup validation for negative values, for two reasons: the
existing `if seconds > 0` guard already treats them as "disabled", and the neighbouring
env-driven timeouts in this file are less strict still -- RelayIdleConnTimeout is
converted with no guard at all. Failing startup on a bad value would be a behaviour
change out of step with the rest of the file; happy to add it if you'd prefer that
direction repo-wide.

Test style: switched to testify (require.Equal / require.Zero / require.Positive), which
is what every other test under service/ uses.

go build, go vet and go test ./common/... ./service/... pass.
(`go build ./...` fails on the `web/dist` embed both with and without this change -- the
frontend bundle is not checked in.)