time/ISO8601: support omitting field separators

NEWS

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

src/time/ISO8601.cxx

@@ -123,8 +123,12 @@ ParseISO8601(const char *s)
 
 	/* parse the date */
 	const char *end = strptime(s, "%F", &tm);
-	if (end == nullptr)
-		throw std::runtime_error("Failed to parse date");
+	if (end == nullptr) {
+		/* try without field separators */
+		end = strptime(s, "%Y%m%d", &tm);
+		if (end == nullptr)
+			throw std::runtime_error("Failed to parse date");
+	}
 
 	s = end;
 
@@ -136,6 +140,12 @@ ParseISO8601(const char *s)
 
 		if ((end = strptime(s, "%T", &tm)) != nullptr)
 			precision = std::chrono::seconds(1);
+		else if ((end = strptime(s, "%H%M%S", &tm)) != nullptr)
+			/* no field separators */
+			precision = std::chrono::seconds(1);
+		else if ((end = strptime(s, "%H%M", &tm)) != nullptr)
+			/* no field separators */
+			precision = std::chrono::minutes(1);
 		else if ((end = strptime(s, "%H:%M", &tm)) != nullptr)
 			precision = std::chrono::minutes(1);
 		else if ((end = strptime(s, "%H", &tm)) != nullptr)

test/TestISO8601.cxx

@@ -71,6 +71,15 @@ static constexpr struct {
 	{ "2019-02-04T16:46:41+0200", 1549291601, std::chrono::seconds(1) },
 	{ "2019-02-04T16:46:41+02:00", 1549291601, std::chrono::seconds(1) },
 	{ "2019-02-04T16:46:41-0200", 1549306001, std::chrono::seconds(1) },
+
+	/* without field separators */
+	{ "19700101T000000Z", 0, std::chrono::seconds(1) },
+	{ "19700101T000001Z", 1, std::chrono::seconds(1) },
+	{ "20190204T164641Z", 1549298801, std::chrono::seconds(1) },
+	{ "19700101", 0, std::chrono::hours(24) },
+	{ "20190204", 1549238400, std::chrono::hours(24) },
+	{ "20190204T1646", 1549298760, std::chrono::minutes(1) },
+	{ "20190204T16", 1549296000, std::chrono::hours(1) },
 };
 
 TEST(ISO8601, Parse)