GMT expiry display

Change solution to display GMT time in the local display format with
the offset number of hours from GMT to be clear about what timezone
this is if the local display format does not include offset.

plugins/sslutils.c

@@ -197,6 +197,7 @@ int np_net_ssl_check_cert(int days_till_exp_warn, int days_till_exp_crit){
 	X509_NAME *subj=NULL;
 	char timestamp[50] = "";
 	char cn[MAX_CN_LENGTH]= "";
+	char *tz;
 	
 	int cnlen =-1;
 	int status=STATE_UNKNOWN;
@@ -267,7 +268,15 @@ int np_net_ssl_check_cert(int days_till_exp_warn, int days_till_exp_crit){
 	tm_t = timegm(&stamp);
 	time_left = difftime(tm_t, time(NULL));
 	days_left = time_left / 86400;
-	strftime(timestamp, 50, "%F %R %z/%Z", localtime(&tm_t));
+	tz = getenv("TZ");
+	setenv("TZ", "GMT", 1);
+	tzset();
+	strftime(timestamp, 50, "%c %z", localtime(&tm_t));
+	if (tz)
+		setenv("TZ", tz, 1);
+	else
+		unsetenv("TZ");
+	tzset();
 
 	if (days_left > 0 && days_left <= days_till_exp_warn) {
 		printf (_("%s - Certificate '%s' expires in %d day(s) (%s).\n"), (days_left>days_till_exp_crit)?"WARNING":"CRITICAL", cn, days_left, timestamp);

plugins/tests/check_http.t

@@ -186,21 +186,21 @@ SKIP: {
 
 	$result = NPTest->testCmd( "$command -p $port_https -S -C 14" );
 	is( $result->return_code, 0, "$command -p $port_https -S -C 14" );
-	is( $result->output, 'OK - Certificate \'Ton Voon\' will expire on Sun Mar  3 21:41:28 2019.', "output ok" );
+	is( $result->output, 'OK - Certificate \'Ton Voon\' will expire on Sun Mar  3 21:41:28 2019 +0000.', "output ok" );
 
 	$result = NPTest->testCmd( "$command -p $port_https -S -C 14000" );
 	is( $result->return_code, 1, "$command -p $port_https -S -C 14000" );
-	like( $result->output, '/WARNING - Certificate \'Ton Voon\' expires in \d+ day\(s\) \(Sun Mar  3 21:41:28 2019\)./', "output ok" );
+	like( $result->output, '/WARNING - Certificate \'Ton Voon\' expires in \d+ day\(s\) \(Sun Mar  3 21:41:28 2019 \+0000\)./', "output ok" );
 
 	# Expired cert tests
 	$result = NPTest->testCmd( "$command -p $port_https -S -C 13960,14000" );
 	is( $result->return_code, 2, "$command -p $port_https -S -C 13960,14000" );
-	like( $result->output, '/CRITICAL - Certificate \'Ton Voon\' expires in \d+ day\(s\) \(Sun Mar  3 21:41:28 2019\)./', "output ok" );
+	like( $result->output, '/CRITICAL - Certificate \'Ton Voon\' expires in \d+ day\(s\) \(Sun Mar  3 21:41:28 2019 \+0000\)./', "output ok" );
 
 	$result = NPTest->testCmd( "$command -p $port_https_expired -S -C 7" );
 	is( $result->return_code, 2, "$command -p $port_https_expired -S -C 7" );
 	is( $result->output,
-		'CRITICAL - Certificate \'Ton Voon\' expired on Thu Mar  5 00:13:16 2009.',
+		'CRITICAL - Certificate \'Ton Voon\' expired on Thu Mar  5 00:13:16 2009 +0000.',
 		"output ok" );
 
 }