Setting hard limit on message/TextPayload to 100000B

Because GCP has a hard limit on 100KB (102400B) and I use the remaining
2400B on the other fields like timestamp and so on.

Author: karl-gustav

README.md

@@ -24,6 +24,6 @@ func init() {
 func main() {
 	log.Info("Hello", "world")
 	log.Infof("Hello %s", "world")
-	log.Infoj(struct{ Hello string }{"world"})
+	log.Infoj("label", struct{ Hello string }{"world"})
 }
 ```

main.go

@@ -23,6 +23,8 @@ const (
 	emergency_severety severety = "EMERGENCY" // One or more systems are unusable.)
 )
 
+const trunkateMessage = "[message over 100Kb, truncating]..."
+
 type Logger struct{}
 
 // StructuredLogger is used to have structured logging in stackdriver (Google Cloud Platform)
@@ -162,6 +164,11 @@ func (l *Logger) writeJson(severety severety, message string, obj interface{}) {
 		return
 	}
 
+	// GCP has max 102400 bytes limit, so setting 100k for message and 2.4k for other fields
+	if len(message) > 100000 {
+		message = message[0:100000-len(trunkateMessage)] + trunkateMessage
+	}
+
 	payload := &stackdriverLogStruct{
 		JsonPayload: obj,
 		TextPayload: message,