From 274ca939e0a5baa74d4ff61518ed0af7b0da5465 Mon Sep 17 00:00:00 2001
From: =?utf8?q?J=C3=A9r=C3=A9mie=20Galarneau?=
 <jeremie.galarneau@efficios.com>
Date: Fri, 17 May 2019 16:03:25 -0400
Subject: [PATCH] Add a time_to_iso8601_str() utility
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time_to_iso8601_str() formats a Unix timestamp to an ISO 8601
compatible string. For now, the only ISO 8601 time format used
in LTTng-tools is the "YYYYmmddTHHMMSS+HHMM" form used by the
session rotation feature.

Since ISO 8601 allows many formats, this functions may need to be
renamed at some point.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---
 src/common/time.c | 33 +++++++++++++++++++++++++++++++++
 src/common/time.h | 12 ++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/src/common/time.c b/src/common/time.c
index a01c16df5..885f58cb1 100644
--- a/src/common/time.c
+++ b/src/common/time.c
@@ -17,6 +17,7 @@
 
 #include <common/time.h>
 #include <common/macros.h>
+#include <common/error.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <limits.h>
@@ -80,3 +81,35 @@ void __attribute__((constructor)) init_locale_utf8_support(void)
 		utf8_output_supported = true;
 	}
 }
+
+LTTNG_HIDDEN
+int time_to_iso8601_str(time_t time, char *str, size_t len)
+{
+	int ret = 0;
+	struct tm *tm_result;
+	struct tm tm_storage;
+	size_t strf_ret;
+
+	if (len < ISO8601_STR_LEN) {
+		ERR("Buffer too short to format ISO 8601 timestamp: %zu bytes provided when at least %zu are needed",
+				len, ISO8601_STR_LEN);
+		ret = -1;
+		goto end;
+	}
+
+        tm_result = localtime_r(&time, &tm_storage);
+	if (!tm_result) {
+		ret = -1;
+		PERROR("Failed to break down timestamp to tm structure");
+		goto end;
+	}
+
+	strf_ret = strftime(str, len, "%Y%m%dT%H%M%S%z", tm_result);
+	if (strf_ret == 0) {
+		ret = -1;
+		ERR("Failed to format timestamp as local time");
+		goto end;
+	}
+end:
+	return ret;
+}
diff --git a/src/common/time.h b/src/common/time.h
index 24513d30b..dc07633e9 100644
--- a/src/common/time.h
+++ b/src/common/time.h
@@ -36,6 +36,8 @@
 #define USEC_PER_MINUTE (USEC_PER_SEC * SEC_PER_MINUTE)
 #define USEC_PER_HOURS  (USEC_PER_MINUTE * MINUTE_PER_HOUR)
 
+#define ISO8601_STR_LEN sizeof("YYYYmmddTHHMMSS+HHMM")
+
 LTTNG_HIDDEN
 bool locale_supports_utf8(void);
 
@@ -61,4 +63,14 @@ int timespec_to_ms(struct timespec ts, unsigned long *ms);
 LTTNG_HIDDEN
 struct timespec timespec_abs_diff(struct timespec ts_a, struct timespec ts_b);
 
+/*
+ * Format a Unix timestamp to an ISO 8601 compatible timestamp of
+ * the form "YYYYmmddTHHMMSS+HHMM" in local time. `len` must >= to
+ * ISO8601_STR_LEN.
+ *
+ * Returns 0 on success, else -1 on error.
+ */
+LTTNG_HIDDEN
+int time_to_iso8601_str(time_t time, char *str, size_t len);
+
 #endif /* LTTNG_TIME_H */
-- 
2.34.1