Fix date format in mosquitto_sub output.

Closes #2353. Thanks to Norman Rasmussen.

ChangeLog.txt

@@ -17,6 +17,9 @@ Client library:
 - Initialise sockpairR/W to invalid in `mosquitto_reinitialise()` to avoid
  closing invalid sockets in `mosquitto_destroy()` on error. Closes #2326.
 
+Clients:
+- Fix date format in mosquitto_sub output. Closes #2353.
+
 
 2.0.12 - 2021-08-31
 ===================

client/sub_client_output.c

@@ -248,6 +248,16 @@ static int json_print_properties(cJSON *root, const mosquitto_property *properti
 #endif
 
 
+static void format_time_8601(const struct tm *ti, int ns, char *buf, size_t len)
+{
+ char c;
+
+ strftime(buf, len, "%Y-%m-%dT%H:%M:%S.000000%z", ti);
+ c = buf[strlen("2020-05-06T21:48:00.000000")];
+ snprintf(&buf[strlen("2020-05-06T21:48:00.")], 9, "%06d", ns/1000);
+ buf[strlen("2020-05-06T21:48:00.000000")] = c;
+}
+
 static int json_print(const struct mosquitto_message *message, const mosquitto_property *properties, const struct tm *ti, int ns, bool escaped, bool pretty)
 {
  char buf[100];
@@ -262,9 +272,7 @@ static int json_print(const struct mosquitto_message *message, const mosquitto_p
  return MOSQ_ERR_NOMEM;
  }
 
- strftime(buf, sizeof(buf), "%Y-%m-%dT%H:%M:%S.000000Z%z", ti);
- snprintf(&buf[strlen("2020-05-06T21:48:00.")], 9, "%06d", ns/1000);
- buf[strlen("2020-05-06T21:48:00.000000")] = 'Z';
+ format_time_8601(ti, ns, buf, sizeof(buf));
 
  tmp = cJSON_CreateStringReference(buf);
  if(tmp == NULL){
@@ -367,9 +375,7 @@ static int json_print(const struct mosquitto_message *message, const mosquitto_p
  UNUSED(properties);
  UNUSED(pretty);
 
- strftime(buf, sizeof(buf), "%Y-%m-%dT%H:%M:%S.000000Z%z", ti);
- snprintf(&buf[strlen("2020-05-06T21:48:00.")], 9, "%06d", ns/1000);
- buf[strlen("2020-05-06T21:48:00.000000")] = 'Z';
+ format_time_8601(ti, ns, buf, sizeof(buf));
 
  printf("{\"tst\":\"%s\",\"topic\":\"%s\",\"qos\":%d,\"retain\":%d,\"payloadlen\":%d,", buf, message->topic, message->qos, message->retain, message->payloadlen);
  if(message->qos > 0){