fix(gotenberg): retry pattern matches aborted by a process pause

pkg/gotenberg/flags.go

@@ -222,6 +222,10 @@ func (f *ParsedFlags) MustDeprecatedHumanReadableBytes(deprecated string, newNam
 // built. Patterns compiled any other way keep regexp2's default of
 // math.MaxInt64, which it treats as no timeout at all, so a hand-built slice
 // must set this itself before reaching [DecideOutbound].
+//
+// The ceiling is wall-clock. Match through [MatchPattern] rather than calling
+// regexp2 directly: a match that never approaches the ceiling still aborts if
+// the process loses the CPU at the wrong moment.
 const PatternMatchTimeout = 250 * time.Millisecond
 
 // MustRegexp returns the regular expression of a flag given by name.

pkg/gotenberg/outbound.go

@@ -336,12 +336,16 @@ func DecideOutbound(ctx context.Context, rawURL string, allowList, denyList []*r
 	allowMatched := false
 	if len(allowList) > 0 {
 		for _, pattern := range allowList {
-			ok, err := pattern.MatchString(normalized)
+			ok, err := MatchPattern(pattern, normalized)
 			if err != nil {
 				if time.Now().After(deadline) {
 					return OutboundDecision{}, context.DeadlineExceeded
 				}
-				return OutboundDecision{}, fmt.Errorf("'%s' cannot handle '%s': %w", pattern.String(), normalized, err)
+				// The pattern could not be evaluated, so the URL cannot be
+				// cleared for the IP-check bypass an allow-list match grants.
+				// Fail closed like an unresolvable host does below, so the
+				// client gets a generic 403 rather than a 500.
+				return OutboundDecision{}, fmt.Errorf("'%s' cannot handle '%s': %v: %w", pattern.String(), normalized, err, ErrFiltered)
 			}
 
 			if ok {
@@ -356,12 +360,15 @@ func DecideOutbound(ctx context.Context, rawURL string, allowList, denyList []*r
 	}
 
 	for _, pattern := range denyList {
-		ok, err := pattern.MatchString(normalized)
+		ok, err := MatchPattern(pattern, normalized)
 		if err != nil {
 			if time.Now().After(deadline) {
 				return OutboundDecision{}, context.DeadlineExceeded
 			}
-			return OutboundDecision{}, fmt.Errorf("'%s' cannot handle '%s': %w", pattern.String(), normalized, err)
+			// The pattern could not be evaluated, so the URL cannot be proven
+			// to fall outside the deny-list. Fail closed rather than letting a
+			// deny-list that never ran pass the request through.
+			return OutboundDecision{}, fmt.Errorf("'%s' cannot handle '%s': %v: %w", pattern.String(), normalized, err, ErrFiltered)
 		}
 
 		if ok {

pkg/gotenberg/outbound_test.go

@@ -793,6 +793,13 @@ func TestDecideOutboundBoundsCatastrophicPatterns(t *testing.T) {
 		t.Fatal("expected an error from a catastrophic deny-list pattern")
 	}
 
+	// A deny-list that could not be evaluated cannot clear the URL, so the
+	// decision fails closed and the client gets a generic 403 rather than a
+	// 500 naming the pattern.
+	if !errors.Is(err, ErrFiltered) {
+		t.Fatalf("expected ErrFiltered from an unevaluable deny-list pattern but got: %v", err)
+	}
+
 	// Generous headroom over the 250ms ceiling, still far below the 30s
 	// deadline the match would otherwise have been allowed to consume.
 	if elapsed > 5*time.Second {

pkg/gotenberg/pattern.go

@@ -0,0 +1,55 @@
+package gotenberg
+
+import (
+	"github.com/dlclark/regexp2"
+)
+
+// patternMatchAttempts caps how many times [MatchPattern] runs one pattern
+// against one string. It is what keeps a pattern that is genuinely out of
+// budget from retrying forever: three attempts bound its cost at three
+// [PatternMatchTimeout], which is still two orders of magnitude below the
+// --api-timeout (env API_TIMEOUT) the ceiling exists to protect.
+const patternMatchAttempts = 3
+
+// MatchPattern reports whether s matches pattern. It bounds the match by the
+// pattern's MatchTimeout without the false timeouts that the bound alone
+// produces.
+//
+// regexp2 does not time a match against [time.Now]. It derives the deadline
+// from a process-global clock that a background goroutine advances every
+// 100ms, and it tests that deadline on the very first step of the match.
+// Anything that stops the whole process, a cgroup CPU-quota throttle or a long
+// stop-the-world pause, also stops that goroutine, which then advances the
+// clock by the full pause in a single write. A match holding a deadline from
+// before that jump aborts whatever work it had done: a 366ns match against a
+// short URL reports "match timeout after 250ms". The abort lands on whichever
+// match straddles the jump rather than on a match that was slow, which is why
+// it fires on an idle instance and against Gotenberg's own file:///tmp/ URLs.
+// See https://github.com/gotenberg/gotenberg/issues/1659.
+//
+// Retrying separates the two cases. Catastrophic backtracking is
+// deterministic: the same pattern against the same string exhausts the same
+// budget on every attempt, so a genuine runaway still aborts, and costs at
+// most patternMatchAttempts ceilings to prove it. A clock-induced abort needs
+// the process to lose the CPU inside one specific match, which the next
+// attempt does not reproduce.
+//
+// Elapsed time cannot make that call instead. A match frozen mid-flight
+// reports the freeze as its own cost, 806ms against a 250ms ceiling in one
+// measured run, so it is indistinguishable by wall clock from a match that
+// really did spend its budget. Go exposes no per-goroutine CPU time, and
+// process CPU time counts every other request in flight.
+func MatchPattern(pattern *regexp2.Regexp, s string) (bool, error) {
+	var err error
+
+	for range patternMatchAttempts {
+		var ok bool
+
+		ok, err = pattern.MatchString(s)
+		if err == nil {
+			return ok, nil
+		}
+	}
+
+	return false, err
+}

pkg/gotenberg/pattern_test.go

@@ -0,0 +1,99 @@
+package gotenberg
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/dlclark/regexp2"
+)
+
+// mustPattern compiles a pattern the way the production lists are built.
+func mustPattern(t *testing.T, expr string) *regexp2.Regexp {
+	t.Helper()
+
+	re := regexp2.MustCompile(expr, 0)
+	re.MatchTimeout = PatternMatchTimeout
+
+	return re
+}
+
+func TestMatchPattern(t *testing.T) {
+	// The abort [MatchPattern] absorbs cannot be staged here: it needs the
+	// whole process to lose the CPU around one specific match, which no test
+	// can schedule. What is testable is the other half of the contract, that
+	// retrying never turns a genuine runaway into a pass.
+	// See https://github.com/gotenberg/gotenberg/issues/1659.
+	for _, tc := range []struct {
+		scenario    string
+		pattern     *regexp2.Regexp
+		s           string
+		expectMatch bool
+		expectError bool
+	}{
+		{
+			scenario:    "deny-list match",
+			pattern:     mustPattern(t, `^file:(?!//\/tmp/).*`),
+			s:           "file:///etc/passwd",
+			expectMatch: true,
+		},
+		{
+			scenario:    "no match against Gotenberg's own working directory",
+			pattern:     mustPattern(t, `^file:(?!//\/tmp/).*`),
+			s:           "file:///tmp/1a2b3c4d/5e6f7a8b/9c0d1e2f.html",
+			expectMatch: false,
+		},
+		{
+			scenario:    "no match",
+			pattern:     mustPattern(t, `^https://example\.com/`),
+			s:           "https://example.org/",
+			expectMatch: false,
+		},
+		{
+			scenario:    "catastrophic backtracking still aborts",
+			pattern:     mustPattern(t, `^https://example\.com/(a+)+$`),
+			s:           "https://example.com/" + strings.Repeat("a", 40) + "!",
+			expectError: true,
+		},
+	} {
+		t.Run(tc.scenario, func(t *testing.T) {
+			ok, err := MatchPattern(tc.pattern, tc.s)
+
+			if tc.expectError && err == nil {
+				t.Fatal("expected an error but got none")
+			}
+
+			if !tc.expectError && err != nil {
+				t.Fatalf("expected no error but got: %v", err)
+			}
+
+			if ok != tc.expectMatch {
+				t.Fatalf("expected match %t but got %t", tc.expectMatch, ok)
+			}
+		})
+	}
+}
+
+func TestMatchPatternBoundsCatastrophicPattern(t *testing.T) {
+	// Proving a runaway is genuine costs one ceiling per attempt, so the
+	// worst case is patternMatchAttempts of them plus regexp2's clock period
+	// on each, roughly a second. The bound that matters is the one this
+	// replaced: before the ceiling existed, the same match was allowed to
+	// burn a core for the caller's whole 30s budget.
+	pattern := mustPattern(t, `^https://example\.com/(a+)+$`)
+	s := "https://example.com/" + strings.Repeat("a", 40) + "!"
+
+	start := time.Now()
+	_, err := MatchPattern(pattern, s)
+	elapsed := time.Since(start)
+
+	if err == nil {
+		t.Fatal("expected an error from a catastrophic pattern")
+	}
+
+	// Generous headroom over the expected second keeps this stable on a
+	// loaded CI box while still failing if the bound is gone.
+	if elapsed > 5*time.Second {
+		t.Fatalf("match took %s, want at most %d ceilings of %s", elapsed, patternMatchAttempts, PatternMatchTimeout)
+	}
+}

pkg/modules/chromium/events.go

@@ -206,7 +206,7 @@ func listenForEventRequestPaused(ctx context.Context, logger *slog.Logger, optio
 						}
 
 						matchStart := time.Now()
-						ok, err := header.Scope.MatchString(e.Request.URL)
+						ok, err := gotenberg.MatchPattern(header.Scope, e.Request.URL)
 						budget.consume(time.Since(matchStart))
 
 						switch {

pkg/modules/chromium/scopebudget_test.go

@@ -7,6 +7,8 @@ import (
 	"time"
 
 	"github.com/dlclark/regexp2"
+
+	"github.com/gotenberg/gotenberg/v8/pkg/gotenberg"
 )
 
 func TestScopeMatchBudget(t *testing.T) {
@@ -90,7 +92,7 @@ func TestScopeMatchBudget_BoundsCatastrophicBacktracking(t *testing.T) {
 			break
 		}
 		matchStart := time.Now()
-		_, _ = pattern.MatchString(url)
+		_, _ = gotenberg.MatchPattern(pattern, url)
 		b.consume(time.Since(matchStart))
 		matched++
 	}
@@ -100,10 +102,13 @@ func TestScopeMatchBudget_BoundsCatastrophicBacktracking(t *testing.T) {
 		t.Errorf("all %d headers were matched, want the budget to stop matching early", headers)
 	}
 
-	// Each match is separately capped at extraHttpHeaderScopeMatchTimeout, so
-	// the worst case is the budget plus one final match that started with the
-	// last of the credit. Generous slack keeps this stable on a loaded CI box.
-	ceiling := budget + extraHttpHeaderScopeMatchTimeout + time.Second
+	// A match that is genuinely out of budget costs a few
+	// extraHttpHeaderScopeMatchTimeout rather than one:
+	// [gotenberg.MatchPattern] retries an abort to tell a real runaway from
+	// one caused by the process losing the CPU. The worst case is the budget
+	// plus one final match that started with the last of the credit. Generous
+	// slack keeps this stable on a loaded CI box.
+	ceiling := budget + 4*extraHttpHeaderScopeMatchTimeout + time.Second
 	if elapsed > ceiling {
 		t.Errorf("matching took %s, want at most %s", elapsed, ceiling)
 	}