Better handling of prefix field

src/github.com/matrix-org/dendrite/common/log.go

@@ -29,7 +29,9 @@ type dendriteFormatter struct {
 	logrus.TextFormatter
 }
 
-func (f dendriteFormatter) Format(entry *logrus.Entry) ([]byte, error) {
+func (f dendriteFormatter) Format(entry *logrus.Entry) (format []byte, err error) {
+	entry.Time = entry.Time.UTC()
+
 	if _, ok := entry.Data["prefix"]; ok {
 		prefix, ok := entry.Data["prefix"].(string)
 		if !ok {
@@ -42,12 +44,27 @@ func (f dendriteFormatter) Format(entry *logrus.Entry) ([]byte, error) {
 			prefix = ansi.Color(prefix, "white+b")
 		}
 
-		entry.Message = fmt.Sprintf("%s: %s", prefix, entry.Message)
+		entry.Message = fmt.Sprintf("%s: %s\t", prefix, entry.Message)
-		delete(entry.Data, "prefix")
+
+		// Generate the formatted log without the prefix as a field
+		// Use a copy of the entry so the same entry isn't altered by multiple
+		// fields at the same time
+		entryCpy := *entry
+		// Go doesn't perform deep copies, so the fields have to be manually
+		// copied
+		fields := make(logrus.Fields)
+		for k, v := range entry.Data {
+			if k != "prefix" {
+				fields[k] = v
+			}
+		}
+		entryCpy.Data = fields
+		format, err = f.TextFormatter.Format(&entryCpy)
+	} else {
+		format, err = f.TextFormatter.Format(entry)
 	}
 
-	entry.Time = entry.Time.UTC()
+	return
-	return f.TextFormatter.Format(entry)
 }
 
 // SetupLogging configures the logging format and destination(s).