time/ISO8601: allow omitting the time of day

NEWS

 ver 0.21.17 (not yet released)
+* protocol
+  - relax the ISO 8601 parser: allow omitting the time of day
 * archive
   - zzip: improve error reporting
 * outputs

src/time/ISO8601.cxx

@@ -70,14 +70,32 @@ ParseISO8601(const char *s)
 	throw std::runtime_error("Time parsing not implemented on Windows");
 #else
 	struct tm tm{};
-	const char *end = strptime(s, "%FT%TZ", &tm);
-	if (end == nullptr || *end != 0)
-		throw std::runtime_error("Failed to parse time stamp");
 
-	std::chrono::system_clock::duration precision = std::chrono::seconds(1);
+	/* parse the date */
+	const char *end = strptime(s, "%F", &tm);
+	if (end == nullptr)
+		throw std::runtime_error("Failed to parse date");
+
+	s = end;
+
+	std::chrono::system_clock::duration precision = std::chrono::hours(24);
+
+	/* parse the time of day */
+	if (*s == 'T') {
+		++s;
+		end = strptime(s, "%TZ", &tm);
+		if (end == nullptr)
+			throw std::runtime_error("Failed to parse time of day");
+
+		s = end;
+		precision = std::chrono::seconds(1);
+	}
 
 	auto tp = TimeGm(tm);
 
+	if (*s != 0)
+		throw std::runtime_error("Garbage at end of time stamp");
+
 	return std::make_pair(tp, precision);
 #endif /* !_WIN32 */
 }

test/TestISO8601.cxx

@@ -45,6 +45,12 @@ static constexpr struct {
 	{ "2019-02-04T16:46:41Z", 1549298801, std::chrono::seconds(1) },
 	{ "2018-12-31T23:59:59Z", 1546300799, std::chrono::seconds(1) },
 	{ "2019-01-01T00:00:00Z", 1546300800, std::chrono::seconds(1) },
+
+	/* only date */
+	{ "1970-01-01", 0, std::chrono::hours(24) },
+	{ "2019-02-04", 1549238400, std::chrono::hours(24) },
+	{ "2018-12-31", 1546214400, std::chrono::hours(24) },
+	{ "2019-01-01", 1546300800, std::chrono::hours(24) },
 };
 
 TEST(ISO8601, Parse)