logging.journaldCore: Fix key encoding of all fields

The encodeJournaldFieldKey function sanitizes the keys for the journald
fields. However, calling the AddTo method on some zap fields results in
multiple output fields. The keys of these additional fields are not
sanitized and may not comply with journald's requirements.

This change applies name sanitation after all fields were added, thereby
including also these surplus fields. As a result, errors are now also
available as "ERROR_VERBOSE", including a potential stack trace.

Author: oxzi

logging/journald_core.go

@@ -67,24 +67,29 @@ func (c *journaldCore) Write(ent zapcore.Entry, fields []zapcore.Field) error {
 	}
 
 	enc := zapcore.NewMapObjectEncoder()
-	// Ensure that all field keys are valid journald field keys. If in doubt, use encodeJournaldFieldKey.
 	c.addFields(enc, fields)
 	c.addFields(enc, c.context)
 	enc.Fields["SYSLOG_IDENTIFIER"] = c.identifier
 
+	// Re-encode keys before passing them to journald. Unfortunately, this cannot be done within addFields or at another
+	// earlier position since zapcore's Field.AddTo may create multiple entries, some with non-compliant names.
+	encFields := make(map[string]interface{})
+	for k, v := range enc.Fields {
+		encFields[encodeJournaldFieldKey(k)] = v
+	}
+
 	message := ent.Message + visibleFieldsMsg(journaldVisibleFields, append(fields, c.context...))
 	if ent.LoggerName != c.identifier {
 		message = ent.LoggerName + ": " + message
 	}
 
-	return journald.Send(message, pri, enc.Fields)
+	return journald.Send(message, pri, encFields)
 }
 
-// addFields adds all given fields to enc with an altered key, prefixed with the journaldCore.identifier and sanitized
-// via encodeJournaldFieldKey.
+// addFields adds all given fields to enc with an altered key, prefixed with the journaldCore.identifier.
 func (c *journaldCore) addFields(enc zapcore.ObjectEncoder, fields []zapcore.Field) {
 	for _, field := range fields {
-		field.Key = encodeJournaldFieldKey(c.identifier + "_" + field.Key)
+		field.Key = c.identifier + "_" + field.Key
 		field.AddTo(enc)
 	}
 }