fix(headers): Add CowStr as a temporary hack to build on beta.

We can revert this PR when rust-lang/rust#23995 lands, but it won't
land until after beta is cut.

src/header/mod.rs

@@ -9,6 +9,7 @@ use std::borrow::{Cow, ToOwned};
 use std::collections::HashMap;
 use std::collections::hash_map::{Iter, Entry};
 use std::iter::{FromIterator, IntoIterator};
+use std::ops::{Deref, DerefMut};
 use std::{mem, fmt};
 
 use {httparse, traitobject};
@@ -26,7 +27,7 @@ mod internals;
 mod shared;
 pub mod parsing;
 
-type HeaderName = UniCase<Cow<'static, str>>;
+type HeaderName = UniCase<CowStr>;
 
 /// A trait for any object that will represent a header field and value.
 ///
@@ -117,7 +118,7 @@ impl Headers {
         let mut headers = Headers::new();
         for header in raw {
             debug!("raw header: {:?}={:?}", header.name, &header.value[..]);
-            let name = UniCase(Cow::Owned(header.name.to_owned()));
+            let name = UniCase(CowStr(Cow::Owned(header.name.to_owned())));
             let mut item = match headers.data.entry(name) {
                 Entry::Vacant(entry) => entry.insert(Item::new_raw(vec![])),
                 Entry::Occupied(entry) => entry.into_mut()
@@ -133,7 +134,7 @@ impl Headers {
     ///
     /// The field is determined by the type of the value being set.
     pub fn set<H: Header + HeaderFormat>(&mut self, value: H) {
-        self.data.insert(UniCase(Cow::Borrowed(header_name::<H>())),
+        self.data.insert(UniCase(CowStr(Cow::Borrowed(header_name::<H>()))),
                          Item::new_typed(Box::new(value)));
     }
 
@@ -150,7 +151,7 @@ impl Headers {
     /// ```
     pub fn get_raw(&self, name: &str) -> Option<&[Vec<u8>]> {
         self.data
-            .get(&UniCase(Cow::Borrowed(unsafe { mem::transmute::<&str, &str>(name) })))
+            .get(&UniCase(CowStr(Cow::Borrowed(unsafe { mem::transmute::<&str, &str>(name) }))))
             .map(Item::raw)
     }
 
@@ -164,22 +165,24 @@ impl Headers {
     /// headers.set_raw("content-length", vec![b"5".to_vec()]);
     /// ```
     pub fn set_raw<K: Into<Cow<'static, str>>>(&mut self, name: K, value: Vec<Vec<u8>>) {
-        self.data.insert(UniCase(name.into()), Item::new_raw(value));
+        self.data.insert(UniCase(CowStr(name.into())), Item::new_raw(value));
     }
 
     /// Remove a header set by set_raw
     pub fn remove_raw(&mut self, name: &str) {
-        self.data.remove(&UniCase(Cow::Borrowed(name)));
+        self.data.remove(
+            &UniCase(CowStr(Cow::Borrowed(unsafe { mem::transmute::<&str, &str>(name) })))
+        );
     }
 
     /// Get a reference to the header field's value, if it exists.
     pub fn get<H: Header + HeaderFormat>(&self) -> Option<&H> {
-        self.data.get(&UniCase(Cow::Borrowed(header_name::<H>()))).and_then(Item::typed::<H>)
+        self.data.get(&UniCase(CowStr(Cow::Borrowed(header_name::<H>())))).and_then(Item::typed::<H>)
     }
 
     /// Get a mutable reference to the header field's value, if it exists.
     pub fn get_mut<H: Header + HeaderFormat>(&mut self) -> Option<&mut H> {
-        self.data.get_mut(&UniCase(Cow::Borrowed(header_name::<H>()))).and_then(Item::typed_mut::<H>)
+        self.data.get_mut(&UniCase(CowStr(Cow::Borrowed(header_name::<H>())))).and_then(Item::typed_mut::<H>)
     }
 
     /// Returns a boolean of whether a certain header is in the map.
@@ -193,13 +196,13 @@ impl Headers {
     /// let has_type = headers.has::<ContentType>();
     /// ```
     pub fn has<H: Header + HeaderFormat>(&self) -> bool {
-        self.data.contains_key(&UniCase(Cow::Borrowed(header_name::<H>())))
+        self.data.contains_key(&UniCase(CowStr(Cow::Borrowed(header_name::<H>()))))
     }
 
     /// Removes a header from the map, if one existed.
     /// Returns true if a header has been removed.
     pub fn remove<H: Header + HeaderFormat>(&mut self) -> bool {
-        self.data.remove(&UniCase(Cow::Borrowed(header_name::<H>()))).is_some()
+        self.data.remove(&UniCase(CowStr(Cow::Borrowed(header_name::<H>())))).is_some()
     }
 
     /// Returns an iterator over the header fields.
@@ -263,7 +266,7 @@ impl<'a> HeaderView<'a> {
     /// Check if a HeaderView is a certain Header.
     #[inline]
     pub fn is<H: Header>(&self) -> bool {
-        UniCase(Cow::Borrowed(header_name::<H>())) == *self.0
+        UniCase(CowStr(Cow::Borrowed(header_name::<H>()))) == *self.0
     }
 
     /// Get the Header name as a slice.
@@ -341,6 +344,42 @@ impl<'a, H: HeaderFormat> fmt::Debug for HeaderFormatter<'a, H> {
     }
 }
 
+#[derive(Clone, Hash, Eq, PartialEq, PartialOrd, Ord)]
+struct CowStr(Cow<'static, str>);
+
+impl Deref for CowStr {
+    type Target = Cow<'static, str>;
+
+    fn deref(&self) -> &Cow<'static, str> {
+        &self.0
+    }
+}
+
+impl fmt::Debug for CowStr {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.0, fmt)
+    }
+}
+
+impl fmt::Display for CowStr {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&self.0, fmt)
+    }
+}
+
+impl DerefMut for CowStr {
+    fn deref_mut(&mut self) -> &mut Cow<'static, str> {
+        &mut self.0
+    }
+}
+
+impl AsRef<str> for CowStr {
+    fn as_ref(&self) -> &str {
+        self
+    }
+}
+
+
 #[cfg(test)]
 mod tests {
     use std::fmt;