feat(headers): add Expires header

src/header/common/util.rs

@@ -2,6 +2,7 @@
 
 use std::str::{FromStr, from_utf8};
 use std::fmt::{mod, Show};
+use time::{Tm, strptime};
 
 /// Reads a single raw string when parsing a header
 pub fn from_one_raw_str<T: FromStr>(raw: &[Vec<u8>]) -> Option<T> {
@@ -43,3 +44,34 @@ pub fn fmt_comma_delimited<T: Show>(fmt: &mut fmt::Formatter, parts: &[T]) -> fm
     }
     Ok(())
 }
+
+/// Get a Tm from HTTP date formats.
+//    Prior to 1995, there were three different formats commonly used by
+//   servers to communicate timestamps.  For compatibility with old
+//   implementations, all three are defined here.  The preferred format is
+//   a fixed-length and single-zone subset of the date and time
+//   specification used by the Internet Message Format [RFC5322].
+//
+//     HTTP-date    = IMF-fixdate / obs-date
+//
+//   An example of the preferred format is
+//
+//     Sun, 06 Nov 1994 08:49:37 GMT    ; IMF-fixdate
+//
+//   Examples of the two obsolete formats are
+//
+//     Sunday, 06-Nov-94 08:49:37 GMT   ; obsolete RFC 850 format
+//     Sun Nov  6 08:49:37 1994         ; ANSI C's asctime() format
+//
+//   A recipient that parses a timestamp value in an HTTP header field
+//   MUST accept all three HTTP-date formats.  When a sender generates a
+//   header field that contains one or more timestamps defined as
+//   HTTP-date, the sender MUST generate those timestamps in the
+//   IMF-fixdate format.
+pub fn tm_from_str(s: &str) -> Option<Tm> {
+    strptime(s, "%a, %d %b %Y %T %Z").or_else(|_| {
+        strptime(s, "%A, %d-%b-%y %T %Z")
+    }).or_else(|_| {
+        strptime(s, "%c")
+    }).ok()
+}