move typed headers and implement FromRequest (#2094)

Co-authored-by: Rob Ede <robjtede@icloud.com>

src/http/header/if_range.rs

@@ -0,0 +1,121 @@
+use std::fmt::{self, Display, Write};
+
+use crate::http::header;
+use crate::error::ParseError;
+use super::{
+    from_one_raw_str, EntityTag, Header, HeaderName, HeaderValue, HttpDate,
+    IntoHeaderValue, InvalidHeaderValue, Writer,
+};
+use crate::HttpMessage;
+
+/// `If-Range` header, defined in [RFC7233](http://tools.ietf.org/html/rfc7233#section-3.2)
+///
+/// If a client has a partial copy of a representation and wishes to have
+/// an up-to-date copy of the entire representation, it could use the
+/// Range header field with a conditional GET (using either or both of
+/// If-Unmodified-Since and If-Match.)  However, if the precondition
+/// fails because the representation has been modified, the client would
+/// then have to make a second request to obtain the entire current
+/// representation.
+///
+/// The `If-Range` header field allows a client to \"short-circuit\" the
+/// second request.  Informally, its meaning is as follows: if the
+/// representation is unchanged, send me the part(s) that I am requesting
+/// in Range; otherwise, send me the entire representation.
+///
+/// # ABNF
+///
+/// ```text
+/// If-Range = entity-tag / HTTP-date
+/// ```
+///
+/// # Example values
+///
+/// * `Sat, 29 Oct 1994 19:43:31 GMT`
+/// * `\"xyzzy\"`
+///
+/// # Examples
+///
+/// ```
+/// use actix_web::HttpResponse;
+/// use actix_web::http::header::{EntityTag, IfRange};
+///
+/// let mut builder = HttpResponse::Ok();
+/// builder.insert_header(
+///     IfRange::EntityTag(
+///         EntityTag::new(false, "abc".to_owned())
+///     )
+/// );
+/// ```
+///
+/// ```
+/// use std::time::{Duration, SystemTime};
+/// use actix_web::{http::header::IfRange, HttpResponse};
+///
+/// let mut builder = HttpResponse::Ok();
+/// let fetched = SystemTime::now() - Duration::from_secs(60 * 60 * 24);
+/// builder.insert_header(
+///     IfRange::Date(fetched.into())
+/// );
+/// ```
+#[derive(Clone, Debug, PartialEq)]
+pub enum IfRange {
+    /// The entity-tag the client has of the resource.
+    EntityTag(EntityTag),
+
+    /// The date when the client retrieved the resource.
+    Date(HttpDate),
+}
+
+impl Header for IfRange {
+    fn name() -> HeaderName {
+        header::IF_RANGE
+    }
+    #[inline]
+    fn parse<T>(msg: &T) -> Result<Self, ParseError>
+    where
+        T: HttpMessage,
+    {
+        let etag: Result<EntityTag, _> =
+            from_one_raw_str(msg.headers().get(&header::IF_RANGE));
+        if let Ok(etag) = etag {
+            return Ok(IfRange::EntityTag(etag));
+        }
+        let date: Result<HttpDate, _> =
+            from_one_raw_str(msg.headers().get(&header::IF_RANGE));
+        if let Ok(date) = date {
+            return Ok(IfRange::Date(date));
+        }
+        Err(ParseError::Header)
+    }
+}
+
+impl Display for IfRange {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            IfRange::EntityTag(ref x) => Display::fmt(x, f),
+            IfRange::Date(ref x) => Display::fmt(x, f),
+        }
+    }
+}
+
+impl IntoHeaderValue for IfRange {
+    type Error = InvalidHeaderValue;
+
+    fn try_into_value(self) -> Result<HeaderValue, Self::Error> {
+        let mut writer = Writer::new();
+        let _ = write!(&mut writer, "{}", self);
+        HeaderValue::from_maybe_shared(writer.take())
+    }
+}
+
+#[cfg(test)]
+mod test_if_range {
+    use super::IfRange as HeaderField;
+    use crate::http::header::*;
+    use std::str;
+
+    test_header!(test1, vec![b"Sat, 29 Oct 1994 19:43:31 GMT"]);
+    test_header!(test2, vec![b"\"abc\""]);
+    test_header!(test3, vec![b"this-is-invalid"], None::<IfRange>);
+}