Fix NormalizePath trailing slash appending

NormalizePath would append a trailing slash if and only if it would
merge multiple slashes into one. For example, the following path would
not get a trailing slash appended:

"/sample/path"

On the other hand, this path would get a trailing slash appended:

"/sample//path"

After this commit, the trailing slash is appended for both the paths.

src/middleware/normalize.rs

@@ -75,14 +75,26 @@ where
     fn call(&mut self, mut req: ServiceRequest) -> Self::Future {
         let head = req.head_mut();
 
+        let original_path = head.uri.path();
+
         // always add trailing slash, might be an extra one
-        let path = head.uri.path().to_string() + "/";
-        let original_len = path.len();
+        let path = original_path.to_string() + "/";
 
         // normalize multiple /'s to one /
         let path = self.merge_slash.replace_all(&path, "/");
 
-        if original_len != path.len() {
+        // Check whether the path has been changed
+        //
+        // This check was previously implemented as string length comparison
+        //
+        // That approach fails when a trailing slash is added,
+        // and a duplicate slash is removed,
+        // since the length of the strings remains the same
+        // 
+        // For example, the path "/v1//s" will be normalized to "/v1/s/"
+        // Both of the paths have the same length, 
+        // so the change can not be deduced from the length comparison
+        if path != original_path {
             let mut parts = head.uri.clone().into_parts();
             let pq = parts.path_and_query.as_ref().unwrap();
 
@@ -178,11 +190,11 @@ mod tests {
     }
 
     #[actix_rt::test]
-    async fn should_normalize_nothing_notrail() {
+    async fn should_normalize_notrail() {
         const URI: &str = "/v1/something";
 
         let srv = |req: ServiceRequest| {
-            assert_eq!(URI, req.path());
+            assert_eq!(URI.to_string() + "/", req.path());
             ok(req.into_response(HttpResponse::Ok().finish()))
         };