Make accessLogEntry a sarama.Encoder.

examples/http_server/http_server.go

@@ -103,21 +103,41 @@ func (s *Server) collectQueryStringData() http.Handler {
 	})
 }
 
-func (s *Server) withAccessLog(next http.Handler) http.Handler {
-	type accessLogEntry struct {
-		Method       string  `json:"method"`
-		Host         string  `json:"host"`
-		Path         string  `json:"path"`
-		IP           string  `json:"ip"`
-		ResponseTime float64 `json:"response_time"`
+type accessLogEntry struct {
+	Method       string  `json:"method"`
+	Host         string  `json:"host"`
+	Path         string  `json:"path"`
+	IP           string  `json:"ip"`
+	ResponseTime float64 `json:"response_time"`
+
+	encoded []byte
+	err     error
+}
+
+func (ale *accessLogEntry) ensureEncoded() {
+	if ale.encoded == nil && ale.err == nil {
+		ale.encoded, ale.err = json.Marshal(ale)
 	}
+}
+
+func (ale *accessLogEntry) Length() int {
+	ale.ensureEncoded()
+	return len(ale.encoded)
+}
+
+func (ale *accessLogEntry) Encode() ([]byte, error) {
+	ale.ensureEncoded()
+	return ale.encoded, ale.err
+}
+
+func (s *Server) withAccessLog(next http.Handler) http.Handler {
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		started := time.Now()
 
 		next.ServeHTTP(w, r)
 
-		entry := accessLogEntry{
+		entry := &accessLogEntry{
 			Method:       r.Method,
 			Host:         r.Host,
 			Path:         r.RequestURI,
@@ -125,18 +145,13 @@ func (s *Server) withAccessLog(next http.Handler) http.Handler {
 			ResponseTime: float64(time.Since(started)) / float64(time.Second),
 		}
 
-		jsonEntry, err := json.Marshal(entry)
-		if err != nil {
-			log.Println("Failed to marshal JSON access log entry:", err)
-		}
-
 		// We will use the client's IP address as key. This will cause
 		// all the access log entries of the same IP address to end up
 		// on the same partition.
 		s.AccessLogProducer.Input() <- &sarama.ProducerMessage{
 			Topic: "access_log",
 			Key:   sarama.StringEncoder(r.RemoteAddr),
-			Value: sarama.ByteEncoder(jsonEntry),
+			Value: entry,
 		}
 	})
 }
@@ -177,7 +192,7 @@ func newAccessLogProducer(brokerList []string) sarama.AsyncProducer {
 		log.Fatalln("Failed to start Sarama producer:", err)
 	}
 
-	// We wil just log to STDOUT if we're not able to produce messages.
+	// We will just log to STDOUT if we're not able to produce messages.
 	// Note: messages will only be returned here after all retry attempts are exhausted.
 	go func() {
 		for err := range producer.Errors() {