Prepare input/file for changes in the registrar

Planned changes in the registrar will introduce a key-value store.
This changes prepares the input/file package for upcoming updates.

filebeat/input/file/state.go

@@ -30,16 +30,16 @@ import (
 
 // State is used to communicate the reading state of a file
 type State struct {
-	Id          string            `json:"-"` // local unique id to make comparison more efficient
-	Finished    bool              `json:"-"` // harvester state
-	Fileinfo    os.FileInfo       `json:"-"` // the file info
-	Source      string            `json:"source"`
-	Offset      int64             `json:"offset"`
-	Timestamp   time.Time         `json:"timestamp"`
-	TTL         time.Duration     `json:"ttl"`
-	Type        string            `json:"type"`
-	Meta        map[string]string `json:"meta"`
-	FileStateOS file.StateOS
+	Id          string            `json:"-" struct:"-"` // local unique id to make comparison more efficient
+	Finished    bool              `json:"-" struct:"-"` // harvester state
+	Fileinfo    os.FileInfo       `json:"-" struct:"-"` // the file info
+	Source      string            `json:"source" struct:"source"`
+	Offset      int64             `json:"offset" struct:"offset"`
+	Timestamp   time.Time         `json:"timestamp" struct:"timestamp"`
+	TTL         time.Duration     `json:"ttl" struct:"ttl"`
+	Type        string            `json:"type"  struct:"type"`
+	Meta        map[string]string `json:"meta" struct:"meta,omitempty"`
+	FileStateOS file.StateOS      `json:"FileStateOS" struct:"FileStateOS"`
 }
 
 // NewState creates a new file state

filebeat/input/file/states.go

@@ -94,6 +94,12 @@ func (s *States) findPrevious(id string) int {
 // The number of states that were cleaned up and number of states that can be
 // cleaned up in the future is returned.
 func (s *States) Cleanup() (int, int) {
+	return s.CleanupWith(nil)
+}
+
+// CleanupWith cleans up the state array. It calls `fn` with the state ID, for
+// each entry to be removed.
+func (s *States) CleanupWith(fn func(string)) (int, int) {
 	s.Lock()
 	defer s.Unlock()
 
@@ -114,7 +120,11 @@ func (s *States) Cleanup() (int, int) {
 				continue
 			}
 
-			delete(s.idx, state.ID())
+			id := state.ID()
+			delete(s.idx, id)
+			if fn != nil {
+				fn(id)
+			}
 			logp.Debug("state", "State removed for %v because of older: %v", state.Source, state.TTL)
 
 			L--