NetServices: Implement BHttpTime, parse_http_time() and format_http_time().

These utilities convert timestamp strings that are formatted according to
the HTTP RFC into BDateTime objects, and vice versa.

Change-Id: Ia2498944fb63d09233839f19d08f15d82a0a9685

headers/private/netservices2/HttpTime.h

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2010-2022 Haiku Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _B_HTTP_TIME_H_
+#define _B_HTTP_TIME_H_
+
+#include <ctime>
+
+#include <DateTime.h>
+#include <ErrorsExt.h>
+#include <String.h>
+
+namespace BPrivate {
+
+namespace Network {
+
+enum class BHttpTimeFormat : int8 {
+	RFC1123 = 0,
+	RFC850,
+	AscTime
+};
+
+
+class BHttpTime {
+public:
+	// Error type
+	class InvalidInput : public BError {
+	public:
+								InvalidInput(const char* origin, BString input);
+
+		virtual	const char*		Message() const noexcept override;
+		virtual	BString			DebugMessage() const override;
+
+		BString					input;
+	};
+
+	// Constructors
+							BHttpTime() noexcept;
+							BHttpTime(BDateTime date);
+							BHttpTime(const BString& dateString);
+
+	// Date modification
+			void			SetTo(const BString& string);
+			void			SetTo(BDateTime date);
+
+
+	// Date Access
+			BDateTime		DateTime() const noexcept;
+			BHttpTimeFormat	DateTimeFormat() const noexcept;
+			BString			ToString(BHttpTimeFormat outputFormat = BHttpTimeFormat::RFC1123) const;
+
+private:
+			void			_Parse(const BString& dateString);
+
+			BDateTime		fDate;
+			BHttpTimeFormat	fDateFormat;
+};
+
+
+// Convenience functions
+BDateTime	parse_http_time(const BString& string);
+BString		format_http_time(BDateTime timestamp,
+	BHttpTimeFormat outputFormat = BHttpTimeFormat::RFC1123);
+
+
+} // namespace Network
+
+} // namespace BPrivate
+
+#endif // _B_HTTP_TIME_H_