Initial example for the Fetch API

examples/fetch/src/lib.rs

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+#![feature(use_extern_macros)]
+
+extern crate wasm_bindgen;
+extern crate js_sys;
+extern crate web_sys;
+extern crate wasm_bindgen_futures;
+extern crate futures;
+#[macro_use]
+extern crate serde_derive;
+
+use wasm_bindgen::prelude::*;
+use wasm_bindgen::JsCast;
+use js_sys::Promise;
+use web_sys::{Request, RequestInit, RequestMode, Response, Window};
+use wasm_bindgen_futures::JsFuture;
+use futures::{future, Future};
+use wasm_bindgen_futures::future_to_promise;
+
+// A struct to hold some data from the github Branch API.
+// Note how we don't have to define every member -- serde will ignore extra data when deserializing
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Branch {
+    pub name: String,
+    pub commit: Commit,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Commit {
+    pub sha: String,
+    pub commit: CommitDetails,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct CommitDetails {
+    pub author: Signature,
+    pub committer: Signature,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Signature {
+    pub name: String,
+    pub email: String,
+}
+
+#[wasm_bindgen]
+extern "C" {
+    static window: Window;
+}
+
+#[wasm_bindgen]
+pub fn run() -> Promise {
+    let mut request_options = RequestInit::new();
+    request_options.method("GET");
+    request_options.mode(RequestMode::Cors);
+
+    let req = Request::new_using_usv_str_and_request_init("https://api.github.com/repos/rustwasm/wasm-bindgen/branches/master", &request_options).unwrap();
+
+    // the RequestInit struct will eventually support setting headers, but that's missing right now
+    req.headers().set("Accept", "application/vnd.github.v3+json").unwrap();
+
+    let req_promise = window.fetch_using_request(&req);
+
+    let to_return = JsFuture::from(req_promise).and_then(|resp_value| {
+        // resp_value is a Response object
+        assert!(resp_value.is_instance_of::<Response>());
+        let resp: Response = resp_value.dyn_into().unwrap();
+
+        resp.json()
+
+
+    }).and_then(|json_value: Promise| {
+        // convert this other promise into a rust Future
+        JsFuture::from(json_value)
+    }).and_then(|json| {
+        // Use serde to parse this into a struct
+        let branch_info: Branch = json.into_serde().unwrap();
+
+        // Send the Branch struct back to javascript as an object
+        future::ok(JsValue::from_serde(&branch_info).unwrap())
+    });
+
+    // Convert this rust future back into a javascript promise.
+    // Return it to javascript so that it can be driven to completion.
+    future_to_promise(to_return)
+}