From 94ccbc0a4f7f63d35a26e475cd28f6f4ee674b9b Mon Sep 17 00:00:00 2001
From: Andrew Ayer <agwa@andrewayer.name>
Date: Mon, 22 Feb 2016 14:11:47 -0800
Subject: [PATCH] Add backoff during fetch errors

---
 scanner.go | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/scanner.go b/scanner.go
index 81abd5c..10ffbaf 100644
--- a/scanner.go
+++ b/scanner.go
@@ -16,6 +16,11 @@ import (
 
 type ProcessCallback func(*Scanner, *ct.LogEntry)
 
+const (
+	FETCH_RETRIES = 10
+	FETCH_RETRY_WAIT = 1
+)
+
 // ScannerOptions holds configuration options for the Scanner
 type ScannerOptions struct {
 	// Number of entries to request in one batch from the Log
@@ -77,16 +82,27 @@ func (s *Scanner) processerJob(id int, entries <-chan ct.LogEntry, processCert P
 	wg.Done()
 }
 
-func (s *Scanner) fetch(r fetchRange, entries chan<- ct.LogEntry, treeBuilder *MerkleTreeBuilder) {
+func (s *Scanner) fetch(r fetchRange, entries chan<- ct.LogEntry, treeBuilder *MerkleTreeBuilder) error {
 	success := false
-	// TODO(alcutter): give up after a while:
+	retries := FETCH_RETRIES
+	retryWait := FETCH_RETRY_WAIT
 	for !success {
 		s.Log(fmt.Sprintf("Fetching entries %d to %d", r.start, r.end))
 		logEntries, err := s.logClient.GetEntries(r.start, r.end)
 		if err != nil {
-			s.Warn(fmt.Sprintf("Problem fetching from log: %s", err.Error()))
-			continue
+			if retries == 0 {
+				s.Warn(fmt.Sprintf("Problem fetching entries %d to %d from log: %s", r.start, r.end, err.Error()))
+				return err
+			} else {
+				s.Log(fmt.Sprintf("Problem fetching entries %d to %d from log (will retry): %s", r.start, r.end, err.Error()))
+				time.Sleep(time.Duration(retryWait) * time.Second)
+				retries--
+				retryWait *= 2
+				continue
+			}
 		}
+		retries = FETCH_RETRIES
+		retryWait = FETCH_RETRY_WAIT
 		for _, logEntry := range logEntries {
 			if treeBuilder != nil {
 				treeBuilder.Add(hashLeaf(logEntry.LeafBytes))
@@ -102,6 +118,7 @@ func (s *Scanner) fetch(r fetchRange, entries chan<- ct.LogEntry, treeBuilder *M
 			success = true
 		}
 	}
+	return nil
 }
 
 // Worker function for fetcher jobs.
@@ -110,6 +127,7 @@ func (s *Scanner) fetch(r fetchRange, entries chan<- ct.LogEntry, treeBuilder *M
 // |entries| channel for the processors to chew on.
 // Will retry failed attempts to retrieve ranges indefinitely.
 // Sends true over the |done| channel when the |ranges| channel is closed.
+/* disabled becuase error handling is broken
 func (s *Scanner) fetcherJob(id int, ranges <-chan fetchRange, entries chan<- ct.LogEntry, wg *sync.WaitGroup) {
 	for r := range ranges {
 		s.fetch(r, entries, nil)
@@ -117,6 +135,7 @@ func (s *Scanner) fetcherJob(id int, ranges <-chan fetchRange, entries chan<- ct
 	s.Log(fmt.Sprintf("Fetcher %d finished", id))
 	wg.Done()
 }
+*/
 
 // Returns the smaller of |a| and |b|
 func min(a int64, b int64) int64 {
@@ -256,7 +275,9 @@ func (s *Scanner) Scan(startIndex int64, endIndex int64, processCert ProcessCall
 	*/
 	for start := startIndex; start < int64(endIndex); {
 		end := min(start+int64(s.opts.BatchSize), int64(endIndex)) - 1
-		s.fetch(fetchRange{start, end}, jobs, treeBuilder)
+		if err := s.fetch(fetchRange{start, end}, jobs, treeBuilder); err != nil {
+			return err
+		}
 		start = end + 1
 	}
 	close(jobs)