From 234278daa045f1153ab292ed6952806bdf5237b5 Mon Sep 17 00:00:00 2001
From: Tristan Wilson <twilson@offchainlabs.com>
Date: Fri, 19 Jul 2024 14:13:52 +0200
Subject: [PATCH] Configurable timeout for HeaderReader polling

Previously if the backend stopped responding the
client.HeaderByNumber call inside the timed main loop would never
return, meaning that if the HeaderReader was only operating in polling
mode, calls to LastHeader would always return the last successfully
fetched header until OldHeaderTimeout, and if that was set to a high
duration then it would effectively always return the last successfully
fetched header and never an error. This would lead to the chain appear
to be stuck and not advancing to clients of HeaderReader.LastHeader.

This change adds a configurable timeout on this call, defaulting to 5s.
Other places in HeaderReader that use LastHeader use the passed-in
context which the client can control, so no extra timeout was added for
these.
---
 util/headerreader/header_reader.go | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/util/headerreader/header_reader.go b/util/headerreader/header_reader.go
index 06dfcfbfa8..074d24338e 100644
--- a/util/headerreader/header_reader.go
+++ b/util/headerreader/header_reader.go
@@ -63,6 +63,7 @@ type Config struct {
 	Enable               bool            `koanf:"enable"`
 	PollOnly             bool            `koanf:"poll-only" reload:"hot"`
 	PollInterval         time.Duration   `koanf:"poll-interval" reload:"hot"`
+	PollTimeout          time.Duration   `koanf:"poll-timeout" reload:"hot"`
 	SubscribeErrInterval time.Duration   `koanf:"subscribe-err-interval" reload:"hot"`
 	TxTimeout            time.Duration   `koanf:"tx-timeout" reload:"hot"`
 	OldHeaderTimeout     time.Duration   `koanf:"old-header-timeout" reload:"hot"`
@@ -80,6 +81,7 @@ var DefaultConfig = Config{
 	Enable:               true,
 	PollOnly:             false,
 	PollInterval:         15 * time.Second,
+	PollTimeout:          5 * time.Second,
 	SubscribeErrInterval: 5 * time.Minute,
 	TxTimeout:            5 * time.Minute,
 	OldHeaderTimeout:     5 * time.Minute,
@@ -94,6 +96,7 @@ func AddOptions(prefix string, f *flag.FlagSet) {
 	f.Bool(prefix+".poll-only", DefaultConfig.PollOnly, "do not attempt to subscribe to header events")
 	f.Bool(prefix+".use-finality-data", DefaultConfig.UseFinalityData, "use l1 data about finalized/safe blocks")
 	f.Duration(prefix+".poll-interval", DefaultConfig.PollInterval, "interval when polling endpoint")
+	f.Duration(prefix+".poll-timeout", DefaultConfig.PollTimeout, "timeout when polling endpoint")
 	f.Duration(prefix+".subscribe-err-interval", DefaultConfig.SubscribeErrInterval, "interval for subscribe error")
 	f.Duration(prefix+".tx-timeout", DefaultConfig.TxTimeout, "timeout when waiting for a transaction")
 	f.Duration(prefix+".old-header-timeout", DefaultConfig.OldHeaderTimeout, "warns if the latest l1 block is at least this old")
@@ -108,6 +111,7 @@ var TestConfig = Config{
 	Enable:           true,
 	PollOnly:         false,
 	PollInterval:     time.Millisecond * 10,
+	PollTimeout:      time.Second * 5,
 	TxTimeout:        time.Second * 5,
 	OldHeaderTimeout: 5 * time.Minute,
 	UseFinalityData:  false,
@@ -287,7 +291,9 @@ func (s *HeaderReader) broadcastLoop(ctx context.Context) {
 			s.possiblyBroadcast(h)
 			timer.Stop()
 		case <-timer.C:
-			h, err := s.client.HeaderByNumber(ctx, nil)
+			timedCtx, cancelFunc := context.WithTimeout(ctx, s.config().PollTimeout)
+			h, err := s.client.HeaderByNumber(timedCtx, nil)
+			cancelFunc()
 			if err != nil {
 				s.setError(fmt.Errorf("failed reading HeaderByNumber: %w", err))
 				if !errors.Is(err, context.Canceled) {