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//! Provides utility function to parse HTTP header value time.

extern crate time;

/// 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<time::Tm> {
    time::strptime(s, "%a, %d %b %Y %T %Z").or_else(|_| {
        time::strptime(s, "%A, %d-%b-%y %T %Z")
    }).or_else(|_| {
        time::strptime(s, "%c")
    }).ok()
}