Refactor backoff again (#1431)

* Tweak backoffs

* Refactor backoff some more, remove BackoffIfRequired as it adds unnecessary complexity

* Ignore 404s

federationsender/statistics/statistics_test.go

@@ -4,8 +4,6 @@ import (
 	"math"
 	"testing"
 	"time"
-
-	"go.uber.org/atomic"
 )
 
 func TestBackoff(t *testing.T) {
@@ -27,34 +25,30 @@ func TestBackoff(t *testing.T) {
 	server.Failure()
 
 	t.Logf("Backoff counter: %d", server.backoffCount.Load())
-	backingOff := atomic.Bool{}
 
 	// Now we're going to simulate backing off a few times to see
 	// what happens.
 	for i := uint32(1); i <= 10; i++ {
-		// Interrupt the backoff - it doesn't really matter if it
-		// completes but we will find out how long the backoff should
-		// have been.
-		interrupt := make(chan bool, 1)
-		close(interrupt)
-
-		// Get the duration.
-		duration, blacklist := server.BackoffIfRequired(backingOff, interrupt)
-
 		// Register another failure for good measure. This should have no
 		// side effects since a backoff is already in progress. If it does
 		// then we'll fail.
 		until, blacklisted := server.Failure()
-		if time.Until(until) > duration {
-			t.Fatal("Failure produced unexpected side effect when it shouldn't have")
-		}
+
+		// Get the duration.
+		_, blacklist := server.BackoffInfo()
+		duration := time.Until(until).Round(time.Second)
+
+		// Unset the backoff, or otherwise our next call will think that
+		// there's a backoff in progress and return the same result.
+		server.cancel()
+		server.backoffStarted.Store(false)
 
 		// Check if we should be blacklisted by now.
 		if i >= stats.FailuresUntilBlacklist {
 			if !blacklist {
 				t.Fatalf("Backoff %d should have resulted in blacklist but didn't", i)
 			} else if blacklist != blacklisted {
-				t.Fatalf("BackoffIfRequired and Failure returned different blacklist values")
+				t.Fatalf("BackoffInfo and Failure returned different blacklist values")
 			} else {
 				t.Logf("Backoff %d is blacklisted as expected", i)
 				continue