feature: filter for raw query strings (#36)

add `warp::query::raw()` filter

A new filter `raw()` creates a `Filter` that returns the raw query
string as type String.

src/filters/query.rs

@@ -21,3 +21,16 @@ pub fn query<T: DeserializeOwned + Send>() -> impl Filter<Extract=One<T>, Error=
             .unwrap_or_else(|| Err(reject::bad_request()))
     })
 }
+
+/// Creates a `Filter` that returns the raw query string as type String.
+pub fn raw() -> impl Filter<Extract=One<String>, Error=Rejection> + Copy {
+    filter_fn_one(|route| {
+        route
+            .query()
+            .map(|q| {
+                q.to_owned()
+            })
+            .map(Ok)
+            .unwrap_or_else(|| Err(reject::bad_request()))
+    })
+}

tests/query.rs

@@ -14,3 +14,14 @@ fn query() {
     assert_eq!(extracted["foo"], "bar");
     assert_eq!(extracted["baz"], "quux");
 }
+
+#[test]
+fn raw_query() {
+    let as_raw = warp::query::raw();
+
+    let req = warp::test::request()
+        .path("/?foo=bar&baz=quux");
+
+    let extracted = req.filter(&as_raw).unwrap();
+    assert_eq!(extracted, "foo=bar&baz=quux".to_owned());
+}