remove some strings

kcl/kcl.go

@@ -51,13 +51,27 @@ func (i ioHandler) readLine() (string, error) {
 	return line, nil
 }
 
+// ActionName is the "action" string contained in the JSON sent from the KCL.
+type ActionName string
+
+const (
+	ActionNameInitialize        ActionName = "initialize"
+	ActionNameProcessRecords               = "processRecords"
+	ActionNameShutdownRequested            = "shutdownRequested"
+	ActionNameShutdown                     = "shutdown"
+	ActionNameCheckpoint                   = "checkpoint"
+)
+
 type ActionInitialize struct {
-	Action            string `json:"action"`
 	ShardID           string `json:"shardId"`
 	SequenceNumber    string `json:"sequenceNumber"`
 	SubSequenceNumber int    `json:"subSequenceNumber"`
 }
 
+func (a ActionInitialize) Name() ActionName {
+	return ActionNameInitialize
+}
+
 type Record struct {
 	SequenceNumber              string `json:"sequenceNumber"`
 	SubSequenceNumber           int    `json:"subSequenceNumber"`
@@ -67,53 +81,63 @@ type Record struct {
 }
 
 type ActionProcessRecords struct {
-	Action             string   `json:"action"`
 	Records            []Record `json:"records"`
 	MillisBehindLatest int      `json:"millisBehindLatest"`
 }
 
+func (a ActionProcessRecords) Name() ActionName {
+	return ActionNameProcessRecords
+}
+
 type ActionShutdown struct {
-	Action string `json:"action"`
 	Reason string `json:"reason"`
 }
 
+func (a ActionShutdown) Name() ActionName {
+	return ActionNameShutdown
+}
+
 type ActionCheckpoint struct {
-	Action            string  `json:"action"`
+	Action            ActionName `json:"action"`
-	SequenceNumber    *string `json:"sequenceNumber,omitempty"`
+	SequenceNumber    *string    `json:"sequenceNumber,omitempty"`
-	SubSequenceNumber *int    `json:"subSequenceNumber,omitempty"`
+	SubSequenceNumber *int       `json:"subSequenceNumber,omitempty"`
-	Error             *string `json:"error,omitempty"`
+	Error             *string    `json:"error,omitempty"`
+}
+
+func (a ActionCheckpoint) Name() ActionName {
+	return ActionNameCheckpoint
 }
 
 func (i ioHandler) loadAction(line string) (interface{}, error) {
 	lineBytes := []byte(line)
 	var message struct {
-		Action string `json:"action"`
+		Action ActionName `json:"action"`
 	}
 	if err := json.Unmarshal(lineBytes, &message); err != nil {
 		return nil, err
 	}
 	switch message.Action {
-	case "initialize":
+	case ActionNameInitialize:
 		var actionInitialize ActionInitialize
 		if err := json.Unmarshal(lineBytes, &actionInitialize); err != nil {
 			return nil, err
 		}
 		return actionInitialize, nil
-	case "processRecords":
+	case ActionNameProcessRecords:
 		var actionProcessRecords ActionProcessRecords
 		if err := json.Unmarshal(lineBytes, &actionProcessRecords); err != nil {
 			return nil, err
 		}
 		return actionProcessRecords, nil
-	case "shutdownRequested":
+	case ActionNameShutdownRequested:
 		fallthrough
-	case "shutdown":
+	case ActionNameShutdown:
 		var actionShutdown ActionShutdown
 		if err := json.Unmarshal(lineBytes, &actionShutdown); err != nil {
 			return nil, err
 		}
 		return actionShutdown, nil
-	case "checkpoint":
+	case ActionNameCheckpoint:
 		var actionCheckpoint ActionCheckpoint
 		if err := json.Unmarshal(lineBytes, &actionCheckpoint); err != nil {
 			return nil, err
@@ -208,31 +232,36 @@ func (kclp *KCLProcess) handleCheckpointAction(action ActionCheckpoint) error {
 
 func (kclp *KCLProcess) sendCheckpoint(seq *string, subSeq *int) error {
 	return kclp.ioHandler.writeAction(ActionCheckpoint{
-		Action:            "checkpoint",
+		Action:            ActionNameCheckpoint,
 		SequenceNumber:    seq,
 		SubSequenceNumber: subSeq,
 	})
 }
 
-func (kclp *KCLProcess) reportDone(responseFor string) error {
+func (kclp *KCLProcess) reportDone(responseFor ActionName) error {
 	return kclp.ioHandler.writeAction(struct {
-		Action      string `json:"action"`
+		Action      string     `json:"action"`
-		ResponseFor string `json:"responseFor"`
+		ResponseFor ActionName `json:"responseFor"`
 	}{
 		Action:      "status",
 		ResponseFor: responseFor,
 	})
 }
 
-func (kclp *KCLProcess) handleLine(line string) (string, error) {
+type Action interface {
+	Name() ActionName
+}
+
+// handleLine processes a line of text sent to the process by the KCL. It returns the action handled, if any.
+func (kclp *KCLProcess) handleLine(line string) (Action, error) {
 	action, err := kclp.ioHandler.loadAction(line)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	switch action := action.(type) {
 	case ActionCheckpoint:
-		return "checkpoint", kclp.handleCheckpointAction(action)
+		return action, kclp.handleCheckpointAction(action)
 	case ActionShutdown:
 		kclp.ioHandler.writeError("Received shutdown action...")
 
@@ -251,23 +280,23 @@ func (kclp *KCLProcess) handleLine(line string) (string, error) {
 			}
 		}
 
-		return "shutdown", kclp.reportDone("shutdown")
+		return action, kclp.reportDone(action.Name())
 	case ActionInitialize:
 		err := kclp.recordProcessor.Initialize(action.ShardID, kclp)
 		if err != nil {
-			return "", err
+			return nil, err
 		}
 
-		return "initialize", kclp.reportDone(action.Action)
+		return action, kclp.reportDone(action.Name())
 	case ActionProcessRecords:
 		err := kclp.recordProcessor.ProcessRecords(action.Records)
 		if err != nil {
-			return "", err
+			return nil, err
 		}
 
-		return "process-record", kclp.reportDone(action.Action)
+		return action, kclp.reportDone(action.Name())
 	default:
-		return "", fmt.Errorf("unknown action to dispatch: %+#v", action)
+		return nil, fmt.Errorf("unknown action to dispatch: %+#v", action)
 	}
 }
 
@@ -288,7 +317,7 @@ func (kclp *KCLProcess) Run() {
 		action, err := kclp.handleLine(line)
 		if err != nil {
 			kclp.ioHandler.writeError(fmt.Sprintf("ERR Handle line: %+#v", err))
-		} else if action == "shutdown" {
+		} else if action != nil && action.Name() == ActionNameShutdown {
 			return
 		}