only support GET requests and 200 OK responses

src/middleware/etaghasher.rs

@@ -1,13 +1,14 @@
 //! ETag header and `304 Not Modified` support for HTTP responses
 ///
 /// The `EtagHasher` middleware generates [RFC
-/// 7232](https://tools.ietf.org/html/rfc7232) ETag headers for HTTP
-/// responses, and checks the ETag for a response against those provided
-/// in the `If-None-Match` header of the request, if present.  In the
-/// event of a match, instead of returning the original response, an
-/// HTTP `304 Not Modified` response with no content is returned
-/// instead.  Only response [Body](enum.Body.html)s of type `Binary` are
-/// supported; responses with other body types will be left unchanged.
+/// 7232](https://tools.ietf.org/html/rfc7232) ETag headers for `200 OK`
+/// responses to HTTP `GET` requests, and checks the ETag for a response
+/// against those provided in the `If-None-Match` header of the request,
+/// if present.  In the event of a match, instead of returning the
+/// original response, an HTTP `304 Not Modified` response with no
+/// content is returned instead.  Only response [Body](enum.Body.html)s
+/// of type `Binary` are supported; responses with other body types will
+/// be left unchanged.
 ///
 /// ETag values are generated by computing a hash function over the
 /// bytes of the body of the original response. Thus, using this
@@ -32,9 +33,7 @@
 /// instance is created; the `DefaultHasher` and `DefaultFilter` can be
 /// used if desired. Currently `DefaultHasher` computes an SHA-1 hash,
 /// but this should not be relied upon. The `DefaultFilter` returns
-/// `true` when the request method is `GET` or `HEAD` and the original
-/// response status is `200 OK`. If you provide your own `filter`, you
-/// will want to check for these conditions as well.
+/// `true` for all `(request, response)` pairs.
 ///
 /// ```rust
 /// # extern crate actix_web;
@@ -131,14 +130,11 @@ impl Hasher for DefaultHasher {
     }
 }
 
-/// Returns `true` when the request method is `GET` or `HEAD` and the
-/// original response status is `200 OK`, and `false` otherwise.
+/// Returns `true` for every `(request, response)` pair.
 pub struct DefaultFilter;
 impl<S> Filter<S> for DefaultFilter {
-    fn filter(&self, req: &HttpRequest<S>, res: &HttpResponse) -> bool {
-        use http::{Method, StatusCode};
-        (*req.method() == Method::GET || *req.method() == Method::HEAD)
-            && res.status() == StatusCode::OK
+    fn filter(&self, _req: &HttpRequest<S>, _res: &HttpResponse) -> bool {
+        true
     }
 }
 
@@ -148,8 +144,17 @@ impl<S> Filter<S> for DefaultFilter {
 /// The `EtagHasher` struct contains a Hasher to compute ETag values for
 /// byte slices and a Filter to determine whether ETag computation and
 /// checking should be applied to a particular (request, response)
-/// pair. Only response [Body](enum.Body.html)s of type `Binary` are
-/// supported; responses with other body types will be left unchanged.
+/// pair.
+///
+/// Middleware processing will be performed only if the following
+/// conditions hold:
+///
+/// * The request method is `GET`
+/// * The status of the original response is `200 OK`
+/// * The type of the original response [Body](enum.Body.html) is `Binary`
+///
+/// If any of these conditions is false, the original response will be
+/// passed through unmodified.
 pub struct EtagHasher<S, H, F>
 where
     S: 'static,
@@ -186,10 +191,12 @@ where
     fn response(
         &mut self, req: &mut HttpRequest<S>, mut res: HttpResponse,
     ) -> Result<middleware::Response> {
+        use http::{Method, StatusCode};
         use header;
         use Body;
 
-        if !self.filter.filter(req, &res) {
+        let valid = *req.method() == Method::GET && res.status() == StatusCode::OK;
+        if !(valid && self.filter.filter(req, &res)) {
             return Ok(middleware::Response::Done(res));
         }