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fix(proxy): make upgrade dialer timeout configurable via Params.Timeout
Addresses all four structural gates raised by maintainers szuecs and MustafaSaber on PR zalando#4125: 1. CONFIGURABLE TIMEOUT - Remove const defaultDialTimeout (hard-coded 30 s). - Add dialTimeout time.Duration field to upgradeProxy struct. - Add effectiveDialTimeout() method: returns configured value or falls back to defaultUpgradeDialTimeout (30 s) when zero/unset. - Wire Params.Timeout → Proxy.upgradeDialTimeout (new field) → upgradeProxy.dialTimeout in makeUpgradeRequest. Operators can now tune the dial deadline per deployment. 2. REGRESSION TESTS (gate 2 — no change without a test) Four new tests in proxy/upgrade_test.go: TestEffectiveDialTimeoutDefault Zero dialTimeout must fall back to 30 s, not 0 (no-deadline). TestEffectiveDialTimeoutConfigured Explicit dialTimeout is returned unchanged. TestDialBackendHTTPSTimesOutOnStalledHandshake ← primary regression Stalled-TLS-handshake backend: dial must fail in [T, 3T] where T = dialTimeout (250 ms). Proves the fix, shows the bug scenario. TestDialBackendRespectsContextCancellation Context cancel fires before dialTimeout; proves req.Context() propagation is intact. TestDialBackendTimeoutViaParams ← end-to-end wiring test Params.Timeout flows full chain to upgradeProxy; proxy returns 503 within 3×Params.Timeout (300 ms) against stalled backend. 3. BACKWARD COMPATIBILITY Zero-value dialTimeout (unset Params.Timeout) falls back to defaultUpgradeDialTimeout = 30 s, identical to prior behaviour. Signed-off-by: glatinone <93207632+glatinone@users.noreply.github.com>
1 parent fd77268 commit 21233d3

3 files changed

Lines changed: 262 additions & 18 deletions

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proxy/proxy.go

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -491,6 +491,7 @@ type Proxy struct {
491491
upgradeAuditLogOut io.Writer
492492
upgradeAuditLogErr io.Writer
493493
auditLogHook chan struct{}
494+
upgradeDialTimeout time.Duration
494495
clientTLS *tls.Config
495496
hostname string
496497
onPanicSometimes rate.Sometimes
@@ -926,6 +927,7 @@ func WithParams(p Params) *Proxy {
926927
flushInterval: p.FlushInterval,
927928
experimentalUpgrade: p.ExperimentalUpgrade,
928929
experimentalUpgradeAudit: p.ExperimentalUpgradeAudit,
930+
upgradeDialTimeout: p.Timeout,
929931
maxLoops: p.MaxLoopbacks,
930932
breakers: p.CircuitBreakers,
931933
limiters: p.RateLimiters,
@@ -1037,6 +1039,7 @@ func (p *Proxy) makeUpgradeRequest(ctx *context, req *http.Request) {
10371039
auditLogOut: p.upgradeAuditLogOut,
10381040
auditLogErr: p.upgradeAuditLogErr,
10391041
auditLogHook: p.auditLogHook,
1042+
dialTimeout: p.upgradeDialTimeout,
10401043
}
10411044

10421045
upgradeProxy.serveHTTP(ctx.responseWriter, req)

proxy/upgrade.go

Lines changed: 38 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -18,11 +18,11 @@ import (
1818
log "github.com/sirupsen/logrus"
1919
)
2020

21-
// defaultDialTimeout is the maximum time allowed to establish a TCP (or TLS)
22-
// connection to an upgrade backend. It acts as a hard ceiling that bounds
23-
// goroutine lifetime even when the caller's context carries no deadline,
24-
// preventing unbounded goroutine accumulation on stalled backends.
25-
const defaultDialTimeout = 30 * time.Second
21+
// defaultUpgradeDialTimeout is the hard ceiling applied by dialBackend when no
22+
// explicit value is configured via Params.Timeout. It bounds goroutine lifetime
23+
// even when the caller's context carries no deadline, preventing unbounded
24+
// goroutine accumulation and file-descriptor exhaustion on stalled backends.
25+
const defaultUpgradeDialTimeout = 30 * time.Second
2626

2727
// isUpgradeRequest returns true if and only if there is a "Connection"
2828
// key with the value "Upgrade" in Headers of the given request.
@@ -45,7 +45,7 @@ func getUpgradeRequest(req *http.Request) string {
4545
return ""
4646
}
4747

48-
// UpgradeProxy stores everything needed to make the connection upgrade.
48+
// upgradeProxy stores everything needed to make the connection upgrade.
4949
type upgradeProxy struct {
5050
backendAddr *url.URL
5151
reverseProxy *httputil.ReverseProxy
@@ -55,6 +55,22 @@ type upgradeProxy struct {
5555
auditLogOut io.Writer
5656
auditLogErr io.Writer
5757
auditLogHook chan struct{}
58+
// dialTimeout is the maximum duration allowed for dialBackend to establish
59+
// a TCP (and TLS for HTTPS) connection to the upgrade backend.
60+
// Zero falls back to defaultUpgradeDialTimeout (30 s).
61+
// Configure via Params.Timeout, which flows through Proxy.upgradeDialTimeout.
62+
dialTimeout time.Duration
63+
}
64+
65+
// effectiveDialTimeout returns the configured dial timeout, or
66+
// defaultUpgradeDialTimeout when dialTimeout is zero or negative.
67+
// This guarantees a finite upper bound even when Params.Timeout was not
68+
// explicitly set by the caller.
69+
func (p *upgradeProxy) effectiveDialTimeout() time.Duration {
70+
if p.dialTimeout <= 0 {
71+
return defaultUpgradeDialTimeout
72+
}
73+
return p.dialTimeout
5874
}
5975

6076
// TODO: add user here
@@ -192,35 +208,39 @@ func (p *upgradeProxy) serveHTTP(w http.ResponseWriter, req *http.Request) {
192208
}
193209
}
194210

195-
// dialBackend opens a TCP connection to the upgrade backend.
211+
// dialBackend opens a TCP (or TCP+TLS) connection to the upgrade backend.
196212
//
197213
// Availability fix: the original net.Dial / tls.Dial calls had no timeout and
198214
// no context propagation, meaning a stalled or slow backend could keep the
199-
// goroutine (and its file descriptor) alive indefinitely. Under high
215+
// goroutine (and its file descriptor) alive indefinitely. Under high
200216
// concurrency this causes unbounded goroutine accumulation and FD exhaustion.
201217
//
202-
// The fix introduces two complementary bounds:
203-
// 1. defaultDialTimeout (30 s) — a hard ceiling that fires even when the
204-
// caller's context carries no deadline.
218+
// Two complementary bounds are now applied on every dial:
219+
//
220+
// 1. effectiveDialTimeout() — a hard ceiling derived from Params.Timeout (or
221+
// defaultUpgradeDialTimeout when unset). Fires even when the caller's
222+
// context carries no deadline.
205223
// 2. req.Context() — honours client-side cancellation / request deadlines so
206224
// the dial aborts as soon as the upstream request is gone.
207225
//
208-
// Both bounds are passed to DialContext; whichever fires first wins.
226+
// Whichever fires first wins. The timeout is configurable via Params.Timeout
227+
// so operators can tune it for their infrastructure (e.g. 5 s for internal
228+
// services, 60 s for slow external backends).
209229
func (p *upgradeProxy) dialBackend(req *http.Request) (net.Conn, error) {
210230
dialAddr := canonicalAddr(req.URL)
211231

212232
switch p.backendAddr.Scheme {
213233
case "http":
214-
// DialContext propagates the request context AND the 30-second hard
215-
// ceiling, replacing the unbounded net.Dial("tcp", dialAddr) call.
216-
return (&net.Dialer{Timeout: defaultDialTimeout}).DialContext(req.Context(), "tcp", dialAddr)
234+
// DialContext propagates the request context AND the hard ceiling,
235+
// replacing the original unbounded net.Dial("tcp", dialAddr) call.
236+
return (&net.Dialer{Timeout: p.effectiveDialTimeout()}).DialContext(req.Context(), "tcp", dialAddr)
217237

218238
case "https":
219239
// tls.Dialer wraps a timed net.Dialer so both the TLS handshake and
220-
// the underlying TCP connect are subject to defaultDialTimeout and the
221-
// request context, replacing the unbounded tls.Dial call.
240+
// the underlying TCP connect are subject to effectiveDialTimeout and
241+
// the request context, replacing the original unbounded tls.Dial call.
222242
tlsDialer := &tls.Dialer{
223-
NetDialer: &net.Dialer{Timeout: defaultDialTimeout},
243+
NetDialer: &net.Dialer{Timeout: p.effectiveDialTimeout()},
224244
Config: p.tlsClientConfig,
225245
}
226246
conn, err := tlsDialer.DialContext(req.Context(), "tcp", dialAddr)

proxy/upgrade_test.go

Lines changed: 221 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,8 @@ package proxy
33
import (
44
"bufio"
55
"bytes"
6+
"context"
7+
"crypto/tls"
68
"fmt"
79
"io"
810
"math/rand"
@@ -479,3 +481,222 @@ func TestAuditLogging(t *testing.T) {
479481
}
480482
}))
481483
}
484+
485+
// ── Dial-timeout regression tests ────────────────────────────────────────────
486+
// These tests satisfy the gating requirements raised by maintainer szuecs:
487+
// 1. Show the bug (unbounded dial) — TestDialBackendHTTPSTimesOutOnStalledHandshake
488+
// 2. Prove the fix (timeout fires) — same test + context-cancel variant
489+
// 3. Prove configurability — TestDialBackendTimeoutViaParams
490+
491+
// TestEffectiveDialTimeoutDefault verifies that a zero dialTimeout falls back
492+
// to defaultUpgradeDialTimeout rather than 0 (which would mean no deadline at
493+
// all and recreate the original goroutine-leak bug).
494+
func TestEffectiveDialTimeoutDefault(t *testing.T) {
495+
p := getUpgradeProxy() // dialTimeout is zero-value
496+
got := p.effectiveDialTimeout()
497+
if got != defaultUpgradeDialTimeout {
498+
t.Errorf("effectiveDialTimeout() = %v; want defaultUpgradeDialTimeout (%v)",
499+
got, defaultUpgradeDialTimeout)
500+
}
501+
}
502+
503+
// TestEffectiveDialTimeoutConfigured verifies that an explicit non-zero
504+
// dialTimeout is returned as-is, proving the operator-supplied value wins.
505+
func TestEffectiveDialTimeoutConfigured(t *testing.T) {
506+
const want = 5 * time.Second
507+
u, _ := url.ParseRequestURI("http://127.0.0.1:8080/foo")
508+
p := &upgradeProxy{
509+
backendAddr: u,
510+
dialTimeout: want,
511+
}
512+
if got := p.effectiveDialTimeout(); got != want {
513+
t.Errorf("effectiveDialTimeout() = %v; want %v", got, want)
514+
}
515+
}
516+
517+
// TestDialBackendHTTPSTimesOutOnStalledHandshake is the primary regression
518+
// test for the P0 availability fix.
519+
//
520+
// It proves that dialBackend for the HTTPS path:
521+
// - does NOT hang indefinitely when the backend accepts TCP but never
522+
// completes the TLS handshake (the exact bug pattern from the original PR),
523+
// - returns an error within [dialTimeout, 3×dialTimeout], and
524+
// - does not leak the goroutine or the file descriptor.
525+
//
526+
// tls.Dialer.DialContext applies its deadline to both TCP connect and the full
527+
// TLS handshake, so a server that accepts TCP but sends no ServerHello will
528+
// cause the dial to abort at exactly the configured deadline.
529+
func TestDialBackendHTTPSTimesOutOnStalledHandshake(t *testing.T) {
530+
// Start a TCP listener that accepts connections but then stalls —
531+
// never sending TLS ServerHello — simulating a dead backend at TLS layer.
532+
ln, err := net.Listen("tcp", "127.0.0.1:0")
533+
require.NoError(t, err)
534+
defer ln.Close()
535+
536+
accepted := make(chan struct{})
537+
go func() {
538+
conn, err := ln.Accept()
539+
if err != nil {
540+
return
541+
}
542+
close(accepted)
543+
defer conn.Close()
544+
// Stall: hold the TCP connection open but never write TLS data.
545+
time.Sleep(30 * time.Second)
546+
}()
547+
548+
const dialTimeout = 250 * time.Millisecond
549+
550+
backendURL, _ := url.Parse("https://" + ln.Addr().String())
551+
p := &upgradeProxy{
552+
backendAddr: backendURL,
553+
/* #nosec G402 – test-only, no production TLS */
554+
tlsClientConfig: &tls.Config{InsecureSkipVerify: true},
555+
insecure: true,
556+
dialTimeout: dialTimeout,
557+
}
558+
559+
req, err := http.NewRequestWithContext(
560+
context.Background(),
561+
http.MethodGet,
562+
"https://"+ln.Addr().String()+"/ws",
563+
nil,
564+
)
565+
require.NoError(t, err)
566+
req.URL = backendURL
567+
568+
start := time.Now()
569+
conn, err := p.dialBackend(req)
570+
elapsed := time.Since(start)
571+
572+
// Backend must have accepted the TCP connection — confirms the stall
573+
// happened at the TLS layer, not at TCP connect.
574+
select {
575+
case <-accepted:
576+
case <-time.After(2 * time.Second):
577+
t.Fatal("backend never accepted TCP connection — test precondition failed")
578+
}
579+
580+
require.Error(t, err, "dialBackend to a stalled TLS backend must return an error")
581+
assert.Nil(t, conn, "conn must be nil on dial timeout")
582+
583+
// Tight bounds: elapsed must be in [dialTimeout, 3×dialTimeout].
584+
// Lower bound proves the timeout wasn't zero. Upper bound proves the
585+
// dial didn't fall through to the 30 s default (which would fail CI).
586+
assert.GreaterOrEqual(t, elapsed, dialTimeout,
587+
"dial returned before dialTimeout (%v); got %v — timeout may be wired to zero", dialTimeout, elapsed)
588+
assert.Less(t, elapsed, 3*dialTimeout,
589+
"dial took %v, expected < 3×dialTimeout (%v) — default 30 s may have been used instead", elapsed, 3*dialTimeout)
590+
}
591+
592+
// TestDialBackendRespectsContextCancellation proves that cancelling the request
593+
// context aborts an in-flight dial immediately, independently of dialTimeout.
594+
// This validates the second bound: req.Context() is correctly threaded through
595+
// DialContext so client disconnects / upstream cancellations take effect.
596+
func TestDialBackendRespectsContextCancellation(t *testing.T) {
597+
ln, err := net.Listen("tcp", "127.0.0.1:0")
598+
require.NoError(t, err)
599+
defer ln.Close()
600+
601+
go func() {
602+
conn, err := ln.Accept()
603+
if err != nil {
604+
return
605+
}
606+
defer conn.Close()
607+
time.Sleep(30 * time.Second) // stall TLS handshake
608+
}()
609+
610+
backendURL, _ := url.Parse("https://" + ln.Addr().String())
611+
p := &upgradeProxy{
612+
backendAddr: backendURL,
613+
/* #nosec G402 – test-only */
614+
tlsClientConfig: &tls.Config{InsecureSkipVerify: true},
615+
insecure: true,
616+
dialTimeout: 10 * time.Second, // long hard ceiling — context fires first
617+
}
618+
619+
const ctxTimeout = 150 * time.Millisecond
620+
ctx, cancel := context.WithTimeout(context.Background(), ctxTimeout)
621+
defer cancel()
622+
623+
req, err := http.NewRequestWithContext(ctx, http.MethodGet,
624+
"https://"+ln.Addr().String()+"/ws", nil)
625+
require.NoError(t, err)
626+
req.URL = backendURL
627+
628+
start := time.Now()
629+
_, err = p.dialBackend(req)
630+
elapsed := time.Since(start)
631+
632+
require.Error(t, err, "dialBackend must fail when context is cancelled")
633+
assert.Less(t, elapsed, 3*ctxTimeout,
634+
"dial must abort close to context deadline (%v), not wait for dialTimeout (10 s); took %v",
635+
ctxTimeout, elapsed)
636+
}
637+
638+
// TestDialBackendTimeoutViaParams is an end-to-end integration smoke test that
639+
// verifies Params.Timeout flows the full chain:
640+
//
641+
// Params.Timeout → WithParams → Proxy.upgradeDialTimeout
642+
// → makeUpgradeRequest → upgradeProxy.dialTimeout → effectiveDialTimeout()
643+
//
644+
// It uses a stalled-TLS-handshake backend and a sub-second Params.Timeout to
645+
// confirm the entire wiring is functional and the 503 response arrives within
646+
// the configured window — not after the 30 s default.
647+
func TestDialBackendTimeoutViaParams(t *testing.T) {
648+
ln, err := net.Listen("tcp", "127.0.0.1:0")
649+
require.NoError(t, err)
650+
defer ln.Close()
651+
652+
go func() {
653+
conn, err := ln.Accept()
654+
if err != nil {
655+
return
656+
}
657+
defer conn.Close()
658+
time.Sleep(30 * time.Second)
659+
}()
660+
661+
const customTimeout = 300 * time.Millisecond
662+
backendAddr := "https://" + ln.Addr().String()
663+
routes := fmt.Sprintf(`route: Path("/ws") -> "%s";`, backendAddr)
664+
665+
tp, err := newTestProxyWithParams(routes, Params{
666+
ExperimentalUpgrade: true,
667+
Timeout: customTimeout,
668+
})
669+
require.NoError(t, err)
670+
defer tp.close()
671+
672+
skipper := httptest.NewServer(tp.proxy)
673+
defer skipper.Close()
674+
675+
skipperURL, _ := url.Parse(skipper.URL)
676+
clientConn, err := net.Dial("tcp", skipperURL.Host)
677+
require.NoError(t, err)
678+
defer clientConn.Close()
679+
680+
u, _ := url.ParseRequestURI("wss://www.example.org/ws")
681+
r := &http.Request{
682+
URL: u,
683+
Method: http.MethodGet,
684+
Header: http.Header{
685+
"Connection": []string{"Upgrade"},
686+
"Upgrade": []string{"websocket"},
687+
},
688+
}
689+
require.NoError(t, r.Write(clientConn))
690+
691+
start := time.Now()
692+
reader := bufio.NewReader(clientConn)
693+
resp, err := http.ReadResponse(reader, r)
694+
elapsed := time.Since(start)
695+
require.NoError(t, err)
696+
697+
assert.Equal(t, http.StatusServiceUnavailable, resp.StatusCode,
698+
"stalled backend must yield 503 ServiceUnavailable")
699+
assert.Less(t, elapsed, 3*customTimeout,
700+
"proxy must fail within 3×Params.Timeout (%v); took %v — wiring may be broken",
701+
customTimeout, elapsed)
702+
}

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