chore(clbot): Refactor backoff utility into a separate package. r/963

It'll be reused by the IRC side of things too.

Change-Id: I3d84f3fd5fca6a6d948f331143b14f096d10675d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/342
Reviewed-by: tazjin <mail@tazj.in>

4 files changed, 60 insertions, 28 deletions

diff --git a/fun/clbot/backoffutil/backoffutil.go b/fun/clbot/backoffutil/backoffutil.go
new file mode 100644
index 0000000000..1b1ea5f9d0
--- /dev/null
+++ b/fun/clbot/backoffutil/backoffutil.go
@@ -0,0 +1,43 @@
+// Package backoffutil provides useful utilities for backoff.
+package backoffutil
+
+import (
+	"time"
+
+	backoff "github.com/cenkalti/backoff/v4"
+)
+
+// ZeroStartingBackOff is a backoff.BackOff that returns "0" as the first Duration after a reset.
+// This is useful for constructing loops and just enforcing a backoff duration on every loop, rather than incorporating this logic into the loop directly.
+type ZeroStartingBackOff struct {
+	bo      backoff.BackOff
+	initial bool
+}
+
+// NewZeroStartingBackOff creates a new ZeroStartingBackOff.
+func NewZeroStartingBackOff(bo backoff.BackOff) *ZeroStartingBackOff {
+	return &ZeroStartingBackOff{bo: bo, initial: true}
+}
+
+// NewDefaultBackOff creates a sensibly configured BackOff that starts at zero.
+func NewDefaultBackOff() backoff.BackOff {
+	ebo := backoff.NewExponentialBackOff()
+	ebo.MaxElapsedTime = 0
+	return NewZeroStartingBackOff(ebo)
+}
+
+// NextBackOff returns the next back off duration to use.
+// For the first call after a call to Reset(), this is 0. For each subsequent duration, the underlying BackOff is consulted.
+func (bo *ZeroStartingBackOff) NextBackOff() time.Duration {
+	if bo.initial == true {
+		bo.initial = false
+		return 0
+	}
+	return bo.bo.NextBackOff()
+}
+
+// Reset resets to the initial state, and also passes a Reset through to the underlying BackOff.
+func (bo *ZeroStartingBackOff) Reset() {
+	bo.initial = true
+	bo.bo.Reset()
+}
diff --git a/fun/clbot/backoffutil/default.nix b/fun/clbot/backoffutil/default.nix
new file mode 100644
index 0000000000..78585da236
--- /dev/null
+++ b/fun/clbot/backoffutil/default.nix
@@ -0,0 +1,14 @@
+{ depot, ... }:
+
+let
+  inherit (depot.third_party) gopkgs;
+in
+depot.nix.buildGo.package {
+  name = "code.tvl.fyi/fun/clbot/backoffutil";
+  srcs = [
+    ./backoffutil.go
+  ];
+  deps = [
+    gopkgs."github.com".cenkalti.backoff.gopkg
+  ];
+}
diff --git a/fun/clbot/gerrit/default.nix b/fun/clbot/gerrit/default.nix
index 725b400e6c..3b6ce0a739 100644
--- a/fun/clbot/gerrit/default.nix
+++ b/fun/clbot/gerrit/default.nix
@@ -11,7 +11,7 @@ depot.nix.buildGo.package {
   ];
   deps = [
     clbot.gerrit.gerritevents
-    gopkgs."github.com".cenkalti.backoff.gopkg
+    clbot.backoffutil
     gopkgs."github.com".golang.glog.gopkg
     gopkgs."golang.org".x.crypto.ssh.gopkg
   ];
diff --git a/fun/clbot/gerrit/watcher.go b/fun/clbot/gerrit/watcher.go
index 80a431f922..d45876129b 100644
--- a/fun/clbot/gerrit/watcher.go
+++ b/fun/clbot/gerrit/watcher.go
@@ -9,35 +9,12 @@ import (
 	"strings"
 	"time"
 
+	"code.tvl.fyi/fun/clbot/backoffutil"
 	"code.tvl.fyi/fun/clbot/gerrit/gerritevents"
-	"github.com/cenkalti/backoff/v4"
 	log "github.com/golang/glog"
 	"golang.org/x/crypto/ssh"
 )
 
-// zeroStartingBackOff is a backoff.BackOff that returns "0" as the first Duration after a reset.
-// This is useful for constructing loops and just enforcing a backoff duration on every loop, rather than incorporating this logic into the loop directly.
-type zeroStartingBackOff struct {
-	bo      backoff.BackOff
-	initial bool
-}
-
-// NextBackOff returns the next back off duration to use.
-// For the first call after a call to Reset(), this is 0. For each subsequent duration, the underlying BackOff is consulted.
-func (bo *zeroStartingBackOff) NextBackOff() time.Duration {
-	if bo.initial == true {
-		bo.initial = false
-		return 0
-	}
-	return bo.bo.NextBackOff()
-}
-
-// Reset resets to the initial state, and also passes a Reset through to the underlying BackOff.
-func (bo *zeroStartingBackOff) Reset() {
-	bo.initial = true
-	bo.bo.Reset()
-}
-
 // closer provides an embeddable implementation of Close which awaits a main loop acknowledging it has stopped.
 type closer struct {
 	stop    chan struct{}
@@ -174,9 +151,7 @@ func (c *restartingClient) runOnce() error {
 
 func (c *restartingClient) run() {
 	defer close(c.stopped)
-	ebo := backoff.NewExponentialBackOff()
-	ebo.MaxElapsedTime = 0
-	bo := &zeroStartingBackOff{bo: ebo, initial: true}
+	bo := backoffutil.NewDefaultBackOff()
 	for {
 		timer := time.NewTimer(bo.NextBackOff())
 		select {