time/ISO8601: refactor ParseTimeOfDay() to parse one by one

NEWS

 ver 0.21.18 (not yet released)
+* protocol
+  - work around Mac OS X bug in the ISO 8601 parser
 * output
   - alsa: fix hang bug with ALSA "null" outputs
 * storage

src/time/ISO8601.cxx

@@ -112,23 +112,58 @@ static const char *
 ParseTimeOfDay(const char *s, struct tm &tm,
 	       std::chrono::system_clock::duration &precision) noexcept
 {
-	const char *end;
+	/* this function always checks "end==s" to work around a
+	   strptime() bug on OS X: if nothing could be parsed,
+	   strptime() returns the input string (indicating success)
+	   instead of nullptr (indicating error) */
 
-	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)
+	const char *end = strptime(s, "%H", &tm);
+	if (end == nullptr || end == s)
+		return end;
+
+	s = end;
+	precision = std::chrono::hours(1);
+
+	if (*s == ':') {
+		/* with field separators: now a minute must follow */
+
+		++s;
+
+		end = strptime(s, "%M", &tm);
+		if (end == nullptr || end == s)
+			return nullptr;
+
+		s = end;
 		precision = std::chrono::minutes(1);
-	else if ((end = strptime(s, "%H", &tm)) != nullptr)
-		precision = std::chrono::hours(1);
-	else
-		return nullptr;
 
+		/* the "seconds" field is optional */
+		if (*s != ':')
+			return s;
+
+		++s;
+
+		end = strptime(s, "%S", &tm);
+		if (end == nullptr || end == s)
+			return nullptr;
+
+		precision = std::chrono::seconds(1);
+		return end;
+	}
+
+	/* without field separators */
+
+	end = strptime(s, "%M", &tm);
+	if (end == nullptr || end == s)
+		return s;
+
+	s = end;
+	precision = std::chrono::minutes(1);
+
+	end = strptime(s, "%S", &tm);
+	if (end == nullptr || end == s)
+		return s;
+
+	precision = std::chrono::seconds(1);
 	return end;
 }