feat(headers): add IfUnmodifiedSince header

This adds support for the If-Unmodified-Since header, and is a trivially
edited version of IfModifiedSince.

src/header/common/if_unmodified_since.rs

@@ -0,0 +1,45 @@
+use std::fmt;
+use std::str::FromStr;
+use time::Tm;
+use header::{Header, HeaderFormat};
+use header::parsing::from_one_raw_str;
+use header::parsing::tm_from_str;
+
+/// The `If-Unmodified-Since` header field.
+#[derive(Copy, PartialEq, Clone, Debug)]
+pub struct IfUnmodifiedSince(pub Tm);
+
+deref!(IfUnmodifiedSince => Tm);
+
+impl Header for IfUnmodifiedSince {
+    fn header_name() -> &'static str {
+        "If-Unmodified-Since"
+    }
+
+    fn parse_header(raw: &[Vec<u8>]) -> Option<IfUnmodifiedSince> {
+        from_one_raw_str(raw)
+    }
+}
+
+
+impl HeaderFormat for IfUnmodifiedSince {
+    fn fmt_header(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        let tm = self.0;
+        let tm = match tm.tm_utcoff {
+            0 => tm,
+            _ => tm.to_utc(),
+        };
+        fmt::Display::fmt(&tm.rfc822(), fmt)
+    }
+}
+
+impl FromStr for IfUnmodifiedSince {
+    type Err = ();
+    fn from_str(s: &str) -> Result<IfUnmodifiedSince, ()> {
+        tm_from_str(s).map(IfUnmodifiedSince).ok_or(())
+    }
+}
+
+bench_header!(imf_fixdate, IfUnmodifiedSince, { vec![b"Sun, 07 Nov 1994 08:48:37 GMT".to_vec()] });
+bench_header!(rfc_850, IfUnmodifiedSince, { vec![b"Sunday, 06-Nov-94 08:49:37 GMT".to_vec()] });
+bench_header!(asctime, IfUnmodifiedSince, { vec![b"Sun Nov  6 08:49:37 1994".to_vec()] });

src/header/common/mod.rs

@@ -21,6 +21,7 @@ pub use self::etag::Etag;
 pub use self::expires::Expires;
 pub use self::host::Host;
 pub use self::if_modified_since::IfModifiedSince;
+pub use self::if_unmodified_since::IfUnmodifiedSince;
 pub use self::last_modified::LastModified;
 pub use self::location::Location;
 pub use self::pragma::Pragma;
@@ -157,6 +158,7 @@ mod expires;
 mod host;
 mod last_modified;
 mod if_modified_since;
+mod if_unmodified_since;
 mod location;
 mod pragma;
 mod referer;