json: add UNIX timestamp in milliseconds

This extends the "timestamp" field with a UNIX timestamp in milliseconds
representing the current local wall clock time.

The "timestamp" field now has a new subkey:

    "timestamp": {
      "time": "Tue, 25 Feb 2025 11:49:59 GMT",
      "timesecs": 1740484199,
      // new
      "timemillisecs": 1740484199926
    },

This is helpful when one does fine-grained network tests with iperf,
where iperf events need to be aligned with events coming from other
resources. A time resolution based on seconds is too coarse-grained
for that.

It is enough to use milliseconds here, as networking always comes
with small timing offsets and delays. Using microseconds wouldn't
add a benefit.

It is sufficient to only change the code at this place, as the rel time
offset for all further events already includes milliseconds. Currently,
iperf3 prints this time offset in seconds encoded as a double with
a microsecond granularity.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

Author: phip1611

src/iperf_api.c

@@ -944,7 +944,7 @@ mapped_v4_to_regular_v4(char *str)
 void
 iperf_on_connect(struct iperf_test *test)
 {
-    time_t now_secs;
+    struct timespec time_spec;
     const char* rfc1123_fmt = "%a, %d %b %Y %H:%M:%S %Z";
     char now_str[100];
     char ipr[INET6_ADDRSTRLEN];
@@ -953,11 +953,15 @@ iperf_on_connect(struct iperf_test *test)
     struct sockaddr_in *sa_inP;
     struct sockaddr_in6 *sa_in6P;
     socklen_t len;
+    unsigned long long now_millisecs;
 
-    now_secs = time((time_t*) 0);
-    (void) strftime(now_str, sizeof(now_str), rfc1123_fmt, gmtime(&now_secs));
+    clock_gettime(CLOCK_REALTIME, &time_spec);
+    // Unix timestamp in milliseconds (local wall clock time)
+    now_millisecs = time_spec.tv_sec * 1000 + time_spec.tv_nsec / 1000000;
+
+    (void) strftime(now_str, sizeof(now_str), rfc1123_fmt, gmtime(&time_spec.tv_sec));
     if (test->json_output)
-	cJSON_AddItemToObject(test->json_start, "timestamp", iperf_json_printf("time: %s  timesecs: %d", now_str, (int64_t) now_secs));
+	cJSON_AddItemToObject(test->json_start, "timestamp", iperf_json_printf("time: %s  timesecs: %d  timemillisecs: %d", now_str, (int64_t) time_spec.tv_sec, now_millisecs));
     else if (test->verbose)
 	iperf_printf(test, report_time, now_str);
 

src/iperf_time.h

@@ -44,6 +44,9 @@ int iperf_time_diff(struct iperf_time *time1, struct iperf_time *time2, struct i
 
 uint64_t iperf_time_in_usecs(struct iperf_time *time);
 
+/**
+* Returns the time in seconds as double type with a microsecond granularity.
+*/
 double iperf_time_in_secs(struct iperf_time *time);
 
 #endif