fix(lifetimes): correct lifetime pattern to separate out server state from mw state

Correct lifetimes in response to errors found by rust-lang/rust#27641;
the lifetime parameters on request ('a, 'b, 'k) seem to play the
following roles:

'a, 'b -- these represent the processing of this individual request.
They can vary.

'k -- this represents the lifetime of the server's internal, mutable
storage. It is fixed.

If you only have two parameters 'x and 'y to supply, then, the correct
pattern is `'x, 'x, 'y`, because then `'x` plays the role of the
intersection of `'a` and `'b`, but `'y` is pinned to the server's
internal storage.

BREAKING CHANGE:
Most type signatures involving `Request` will have broken, to fix code
broken by this change, you will need to remove the third lifetime.

Author: nikomatsakis

src/favicon_handler.rs

@@ -19,7 +19,7 @@ pub struct FaviconHandler {
 }
 
 impl Middleware for FaviconHandler {
-    fn invoke<'a, 'b>(&'a self, req: &mut Request<'b, 'a, 'b>, res: Response<'a, net::Fresh>)
+    fn invoke<'a, 'b>(&'a self, req: &mut Request<'a, 'a, 'b>, res: Response<'a, net::Fresh>)
             -> MiddlewareResult<'a> {
         if FaviconHandler::is_favicon_request(req) {
             self.handle_request(req, res)

src/macros/middleware.rs

@@ -48,7 +48,7 @@ macro_rules! _middleware_inner {
         #[inline(always)]
         fn restrict_closure<F>(f: F) -> F
             where F: for<'r, 'b, 'a>
-                        Fn(&'r mut Request<'b, 'a, 'b>, Response<'a>)
+                        Fn(&'r mut Request<'a, 'a, 'b>, Response<'a>)
                             -> MiddlewareResult<'a> + Send + Sync { f }
 
         restrict_closure(move |as_pat!($req), $res_binding| {

src/middleware.rs

@@ -17,13 +17,13 @@ pub enum Action<T=(), U=()> {
 // the usage of + Send is weird here because what we really want is + Static
 // but that's not possible as of today. We have to use + Send for now.
 pub trait Middleware: Send + 'static + Sync {
-    fn invoke<'a, 'b>(&'a self, _req: &mut Request<'b, 'a, 'b>, res: Response<'a, net::Fresh>) -> MiddlewareResult<'a> {
+    fn invoke<'a, 'b>(&'a self, _req: &mut Request<'a, 'a, 'b>, res: Response<'a, net::Fresh>) -> MiddlewareResult<'a> {
         Ok(Continue(res))
     }
 }
 
-impl<T> Middleware for T where T: for<'r, 'b, 'a> Fn(&'r mut Request<'b, 'a, 'b>, Response<'a>) -> MiddlewareResult<'a> + Send + Sync + 'static {
-    fn invoke<'a, 'b>(&'a self, req: &mut Request<'b, 'a, 'b>, res: Response<'a>) -> MiddlewareResult<'a> {
+impl<T> Middleware for T where T: for<'r, 'b, 'a> Fn(&'r mut Request<'a, 'a, 'b>, Response<'a>) -> MiddlewareResult<'a> + Send + Sync + 'static {
+    fn invoke<'a, 'b>(&'a self, req: &mut Request<'a, 'a, 'b>, res: Response<'a>) -> MiddlewareResult<'a> {
         (*self)(req, res)
     }
 }

src/request.rs

@@ -5,7 +5,7 @@ use hyper::server::Request as HyperRequest;
 use hyper::uri::RequestUri::AbsolutePath;
 
 ///A container for all the request data
-pub struct Request<'a, 'b: 'k, 'k: 'a> {
+pub struct Request<'a, 'b, 'k: 'a> {
     ///the original `hyper::server::Request`
     pub origin: HyperRequest<'a, 'k>,
     ///a `HashMap<String, String>` holding all params with names and values

src/router/router.rs

@@ -95,7 +95,7 @@ impl HttpRouter for Router {
 }
 
 impl Middleware for Router {
-    fn invoke<'a, 'b>(&'a self, req: &mut Request<'b, 'a, 'b>, mut res: Response<'a>)
+    fn invoke<'a, 'b>(&'a self, req: &mut Request<'a, 'a, 'b>, mut res: Response<'a>)
                         -> MiddlewareResult<'a> {
         debug!("Router::invoke for '{:?}'", req.origin.uri);
 

src/server.rs

@@ -19,9 +19,9 @@ struct ArcServer(Arc<Server>);
 
 impl Handler for ArcServer {
     fn handle<'a, 'k>(&'a self, req: Request<'a, 'k>, res: Response<'a>) {
+        let req: Request<'a, 'k> = req;
         let nickel_req = request::Request::from_internal(req);
         let nickel_res = response::Response::from_internal(res, &self.0.templates);
-
         self.0.middleware_stack.invoke(nickel_req, nickel_res);
     }
 }