Implement more of FetchOptions

Cargo.toml

@@ -43,6 +43,8 @@ wasm-bindgen = "0.2.58"
 
 [target.'cfg(all(target_arch = "wasm32", not(target_os="wasi"), not(cargo_web)))'.dev-dependencies]
 wasm-bindgen-test = "0.3.4"
+base64 = "0.11.0"
+ssri = "5.0.0"
 
 [target.'cfg(target_os = "emscripten")'.dependencies]
 ryu = "1.0.2" # 1.0.1 breaks emscripten

src/callback.rs

@@ -64,3 +64,71 @@ impl<IN: 'static> Callback<IN> {
         Callback::from(func)
     }
 }
+
+#[cfg(test)]
+pub(crate) mod test_util {
+    use super::*;
+    use std::cell::RefCell;
+    use std::future::Future;
+    use std::pin::Pin;
+    use std::task::{Context, Poll, Waker};
+
+    struct CallbackHandle<T> {
+        waker: Option<Waker>,
+        output: Option<T>,
+    }
+
+    impl<T> Default for CallbackHandle<T> {
+        fn default() -> Self {
+            CallbackHandle {
+                waker: None,
+                output: None,
+            }
+        }
+    }
+
+    pub(crate) struct CallbackFuture<T>(Rc<RefCell<CallbackHandle<T>>>);
+
+    impl<T> Clone for CallbackFuture<T> {
+        fn clone(&self) -> Self {
+            Self(self.0.clone())
+        }
+    }
+
+    impl<T> Default for CallbackFuture<T> {
+        fn default() -> Self {
+            Self(Rc::default())
+        }
+    }
+
+    impl<T: 'static> Into<Callback<T>> for CallbackFuture<T> {
+        fn into(self) -> Callback<T> {
+            Callback::from(move |r| self.finish(r))
+        }
+    }
+
+    impl<T> Future for CallbackFuture<T> {
+        type Output = T;
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            if let Some(output) = self.ready() {
+                Poll::Ready(output)
+            } else {
+                self.0.borrow_mut().waker = Some(cx.waker().clone());
+                Poll::Pending
+            }
+        }
+    }
+
+    impl<T> CallbackFuture<T> {
+        fn ready(&self) -> Option<T> {
+            self.0.borrow_mut().output.take()
+        }
+
+        fn finish(&self, output: T) {
+            self.0.borrow_mut().output = Some(output);
+            if let Some(waker) = self.0.borrow_mut().waker.take() {
+                waker.wake();
+            }
+        }
+    }
+}