1 files changed, 81 insertions, 0 deletions
diff --git a/libnetdata/datetime/iso8601.c b/libnetdata/datetime/iso8601.c
new file mode 100644
index 00000000..8e3f4e02
--- /dev/null
+++ b/libnetdata/datetime/iso8601.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "../libnetdata.h"
+
+size_t iso8601_datetime_ut(char *buffer, size_t len, usec_t now_ut, ISO8601_OPTIONS options) {
+    if(unlikely(!buffer || len == 0))
+        return 0;
+
+    time_t t = (time_t)(now_ut / USEC_PER_SEC);
+    struct tm *tmp, tmbuf;
+
+    if(options & ISO8601_UTC)
+        // Use gmtime_r for UTC time conversion.
+        tmp = gmtime_r(&t, &tmbuf);
+    else
+        // Use localtime_r for local time conversion.
+        tmp = localtime_r(&t, &tmbuf);
+
+    if (unlikely(!tmp)) {
+        buffer[0] = '\0';
+        return 0;
+    }
+
+    // Format the date and time according to the ISO 8601 format.
+    size_t used_length = strftime(buffer, len, "%Y-%m-%dT%H:%M:%S", tmp);
+    if (unlikely(used_length == 0)) {
+        buffer[0] = '\0';
+        return 0;
+    }
+
+    if(options & ISO8601_MILLISECONDS) {
+        // Calculate the remaining microseconds
+        int milliseconds = (int) ((now_ut % USEC_PER_SEC) / USEC_PER_MS);
+        if(milliseconds && len - used_length > 4)
+            used_length += snprintfz(buffer + used_length, len - used_length, ".%03d", milliseconds);
+    }
+    else if(options & ISO8601_MICROSECONDS) {
+        // Calculate the remaining microseconds
+        int microseconds = (int) (now_ut % USEC_PER_SEC);
+        if(microseconds && len - used_length > 7)
+            used_length += snprintfz(buffer + used_length, len - used_length, ".%06d", microseconds);
+    }
+
+    if(options & ISO8601_UTC) {
+        if(used_length + 1 < len) {
+            buffer[used_length++] = 'Z';
+            buffer[used_length] = '\0'; // null-terminate the string.
+        }
+    }
+    else {
+        // Calculate the timezone offset in hours and minutes from UTC.
+        long offset = tmbuf.tm_gmtoff;
+        int hours = (int) (offset / 3600); // Convert offset seconds to hours.
+        int minutes = (int) ((offset % 3600) / 60); // Convert remainder to minutes (keep the sign for minutes).
+
+        // Check if timezone is UTC.
+        if(hours == 0 && minutes == 0) {
+            // For UTC, append 'Z' to the timestamp.
+            if(used_length + 1 < len) {
+                buffer[used_length++] = 'Z';
+                buffer[used_length] = '\0'; // null-terminate the string.
+            }
+        }
+        else {
+            // For non-UTC, format the timezone offset. Omit minutes if they are zero.
+            if(minutes == 0) {
+                // Check enough space is available for the timezone offset string.
+                if(used_length + 3 < len) // "+hh\0"
+                    used_length += snprintfz(buffer + used_length, len - used_length, "%+03d", hours);
+            }
+            else {
+                // Check enough space is available for the timezone offset string.
+                if(used_length + 6 < len) // "+hh:mm\0"
+                    used_length += snprintfz(buffer + used_length, len - used_length,
+                                             "%+03d:%02d", hours, abs(minutes));
+            }
+        }
+    }
+
+    return used_length;
+}