Ignore _method field in derived FromForm.

Fixes #45.

codegen/src/decorators/derive_form.rs

@@ -191,6 +191,11 @@ fn from_form_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substruct
         for (k, v) in ::rocket::request::FormItems($arg) {
             match k {
                 $arms
+                field if field == "_method" => {
+                    /* This is a Rocket-specific field. If the user hasn't asked
+                     * for it, just let it go by without error. This should stay
+                     * in sync with Rocket::preprocess. */
+                }
                 _ => {
                     println!("    => {}={} has no matching field in struct.",
                              k, v);

codegen/tests/run-pass/derive_form.rs

@@ -47,6 +47,12 @@ struct DefaultInput<'r> {
     arg: Option<&'r str>,
 }
 
+#[derive(Debug, PartialEq, FromForm)]
+struct ManualMethod<'r> {
+    _method: Option<&'r str>,
+    done: bool
+}
+
 fn main() {
     // Same number of arguments: simple case.
     let task = TodoTask::from_form_string("description=Hello&completed=on");
@@ -59,6 +65,13 @@ fn main() {
     let task = TodoTask::from_form_string("other=a&description=Hello&completed=on");
     assert!(task.is_err());
 
+    // Ensure _method isn't required.
+    let task = TodoTask::from_form_string("_method=patch&description=Hello&completed=off");
+    assert_eq!(task, Ok(TodoTask {
+        description: "Hello".to_string(),
+        completed: false
+    }));
+
     let form_string = &[
         "password=testing", "checkbox=off", "checkbox=on", "number=10",
         "checkbox=off", "textarea=", "select=a", "radio=c",
@@ -79,4 +92,18 @@ fn main() {
     assert_eq!(default, Ok(DefaultInput {
         arg: None
     }));
+
+    // Ensure _method can be captured if desired.
+    let manual = ManualMethod::from_form_string("_method=put&done=true");
+    assert_eq!(manual, Ok(ManualMethod {
+        _method: Some("put"),
+        done: true
+    }));
+
+    // And ignored when not present.
+    let manual = ManualMethod::from_form_string("done=true");
+    assert_eq!(manual, Ok(ManualMethod {
+        _method: None,
+        done: true
+    }));
 }

lib/src/request/form/from_form.rs

@@ -38,9 +38,14 @@ use error::Error;
 /// ```
 ///
 /// When deriving `FromForm`, every field in the structure must implement
-/// [FromFormValue](trait.FromFormValue.html). If you implement `FormForm`
+/// [FromFormValue](trait.FromFormValue.html).
-/// yourself, use the [FormItems](struct.FormItems.html) iterator to iterate
+///
-/// through the form key/value pairs.
+/// # Implementing
+///
+/// If you implement `FormForm` yourself, use the
+/// [FormItems](struct.FormItems.html) iterator to iterate through the form
+/// key/value pairs. Be aware that form fields that are typically hidden from
+/// your application, such as `_method`, will be present while iterating.
 pub trait FromForm<'f>: Sized {
     /// The associated error to be returned when parsing fails.
     type Error;

lib/src/rocket.rs

@@ -75,7 +75,7 @@ impl Rocket {
     #[inline]
     fn issue_response(&self, mut response: Response, hyp_res: hyper::FreshResponse) {
         // Add the 'rocket' server header, and write out the response.
-        // TODO: If removing Hyper, write out `Data` header too.
+        // TODO: If removing Hyper, write out `Date` header too.
         response.set_header(header::Server("rocket".to_string()));
 
         match self.write_response(response, hyp_res) {
@@ -134,7 +134,8 @@ impl Rocket {
     }
 
     /// Preprocess the request for Rocket-specific things. At this time, we're
-    /// only checking for _method in forms.
+    /// only checking for _method in forms. Keep this in-sync with derive_form
+    /// when preprocessing form fields.
     fn preprocess_request(&self, req: &mut Request, data: &Data) {
         // Check if this is a form and if the form contains the special _method
         // field which we use to reinterpret the request's method.
@@ -176,7 +177,7 @@ impl Rocket {
                 // convince it to give us another mutable reference.
                 // FIXME: Pay the cost to copy Request into UnsafeCell? Pay the
                 // cost to use RefCell? Move the call to `issue_response` here
-                // to move Request and move directly into a RefCell?
+                // to move Request and move directly into an UnsafeCell?
                 let request: &'r mut Request = unsafe {
                     &mut *(request as *const Request as *mut Request)
                 };

lib/tests/form_method-issue-45.rs

@@ -0,0 +1,35 @@
+#![feature(plugin, custom_derive)]
+#![plugin(rocket_codegen)]
+
+extern crate rocket;
+
+use rocket::request::Form;
+
+#[derive(FromForm)]
+struct FormData {
+    form_data: String,
+}
+
+#[patch("/", data = "<form_data>")]
+fn bug(form_data: Form<FormData>) -> &'static str {
+    assert_eq!("Form data", &form_data.get().form_data);
+    "OK"
+}
+
+
+use rocket::testing::MockRequest;
+use rocket::http::Method::*;
+use rocket::http::ContentType;
+
+#[test]
+fn method_eval() {
+    let rocket = rocket::ignite().mount("/", routes![bug]);
+
+    let mut req = MockRequest::new(Patch, "/")
+        .header(ContentType::Form)
+        .body("_method=patch&form_data=Form+data");
+
+    let mut response = req.dispatch_with(&rocket);
+    let body_str = response.body().and_then(|b| b.into_string());
+    assert_eq!(body_str, Some("OK".to_string()));
+}