allow basic logging for http Get err with RegisterErrLogFn

rename to follow hook function name convention, log more ctx info

groupcache.go

@@ -26,6 +26,7 @@ package groupcache
 
 import (
  "errors"
+ "fmt"
  "math/rand"
  "strconv"
  "sync"
@@ -60,6 +61,7 @@ var (
 
  initPeerServerOnce sync.Once
  initPeerServer func()
+ errLogHook func(error)
 )
 
 // GetGroup returns the named group previously created with NewGroup, or
@@ -121,6 +123,20 @@ func RegisterNewGroupHook(fn func(*Group)) {
  newGroupHook = fn
 }
 
+// RegisterErrLogHook registers a log func that is used for HTTP error logging.
+func RegisterErrLogHook(fn func(error)) {
+ if errLogHook != nil {
+ panic("RegisterErrLogHook called more than once")
+ }
+ errLogHook = fn
+}
+
+func logErr(err error) {
+ if errLogHook != nil {
+ errLogHook(err)
+ }
+}
+
 // RegisterServerStart registers a hook that is run when the first
 // group is created.
 func RegisterServerStart(fn func()) {
@@ -271,10 +287,7 @@ func (g *Group) load(ctx Context, key string, dest Sink) (value ByteView, destPo
  return value, nil
  }
  g.Stats.PeerErrors.Add(1)
- // TODO(bradfitz): log the peer's error? keep
- // log of the past few for /groupcachez? It's
- // probably boring (normal task movement), so not
- // worth logging I imagine.
+ logErr(fmt.Errorf("%+v, %+v, %+v, %+v", ctx, peer, key, err))
  }
  value, err = g.getLocally(ctx, key, dest)
  if err != nil {