Add encodeBody and cf to ResponseInit. Adopt builder pattern.

Closes #567

worker-sys/src/ext/response_init.rs

@@ -2,17 +2,32 @@ use wasm_bindgen::prelude::*;
 
 pub trait ResponseInitExt {
     /// Change the `webSocket` field of this object.
-    fn websocket(&mut self, val: &web_sys::WebSocket) -> &mut Self;
+    fn websocket(&mut self, val: &web_sys::WebSocket) -> Result<&mut Self, JsValue>;
+
+    /// Change the `encodeBody` field of this object.
+    fn encode_body(&mut self, val: String) -> Result<&mut Self, JsValue>;
+
+    /// Change the `cf` field of this object.
+    fn cf(&mut self, val: &JsValue) -> Result<&mut Self, JsValue>;
 }
 
 impl ResponseInitExt for web_sys::ResponseInit {
-    fn websocket(&mut self, val: &web_sys::WebSocket) -> &mut Self {
-        let r = js_sys::Reflect::set(self.as_ref(), &JsValue::from("webSocket"), val.as_ref());
-        debug_assert!(
-            r.is_ok(),
-            "setting properties should never fail on our dictionary objects"
-        );
-        let _ = r;
-        self
+    fn websocket(&mut self, val: &web_sys::WebSocket) -> Result<&mut Self, JsValue> {
+        js_sys::Reflect::set(self.as_ref(), &JsValue::from("webSocket"), val.as_ref())?;
+        Ok(self)
+    }
+
+    fn encode_body(&mut self, val: String) -> Result<&mut Self, JsValue> {
+        js_sys::Reflect::set(
+            self.as_ref(),
+            &JsValue::from("encodeBody"),
+            &JsValue::from(val),
+        )?;
+        Ok(self)
+    }
+
+    fn cf(&mut self, val: &JsValue) -> Result<&mut Self, JsValue> {
+        js_sys::Reflect::set(self.as_ref(), &JsValue::from("cf"), val)?;
+        Ok(self)
     }
 }