wasm: avoid dependency on serde-serialize feature (#1337)

Using this feature makes dependency cycles much more likely.

Cargo.toml

@@ -149,7 +149,8 @@ winreg = "0.7"
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 js-sys = "0.3.45"
-wasm-bindgen = { version = "0.2.68", features = ["serde-serialize"] }
+serde_json = "1.0"
+wasm-bindgen = "0.2.68"
 wasm-bindgen-futures = "0.4.18"
 
 [target.'cfg(target_arch = "wasm32")'.dependencies.web-sys]
@@ -169,6 +170,7 @@ features = [
 ]
 
 [target.'cfg(target_arch = "wasm32")'.dev-dependencies]
+wasm-bindgen = { version = "0.2.68", features = ["serde-serialize"] }
 wasm-bindgen-test = "0.3"
 
 [[example]]

src/wasm/client.rs

@@ -1,5 +1,5 @@
 use http::{HeaderMap, Method};
-use js_sys::Promise;
+use js_sys::{Promise, JSON};
 use std::{fmt, future::Future, sync::Arc};
 use url::Url;
 use wasm_bindgen::prelude::{wasm_bindgen, UnwrapThrowExt as _};
@@ -238,11 +238,12 @@ async fn fetch(req: Request) -> crate::Result<Response> {
 
     for item in js_iter {
         let item = item.expect_throw("headers iterator doesn't throw");
-        let v: Vec<String> = item.into_serde().expect_throw("headers into_serde");
-        resp = resp.header(
-            v.get(0).expect_throw("headers name"),
-            v.get(1).expect_throw("headers value"),
-        );
+        let serialized_headers: String = JSON::stringify(&item)
+            .expect_throw("serialized headers")
+            .into();
+        let [name, value]: [String; 2] = serde_json::from_str(&serialized_headers)
+            .expect_throw("deserializable serialized headers");
+        resp = resp.header(name, value);
     }
 
     resp.body(js_resp)