feat(swarm): Add wasm-bindgen executor (#3115)

Cargo.toml

@@ -78,7 +78,7 @@ serde = ["libp2p-core/serde", "libp2p-kad?/serde", "libp2p-gossipsub?/serde"]
 tcp = ["dep:libp2p-tcp"]
 tokio = ["libp2p-swarm/tokio", "libp2p-mdns?/tokio", "libp2p-tcp?/tokio", "libp2p-dns?/tokio", "libp2p-quic?/tokio", "libp2p-webrtc?/tokio"]
 uds = ["dep:libp2p-uds"]
-wasm-bindgen = ["futures-timer/wasm-bindgen", "instant/wasm-bindgen", "getrandom/js"]
+wasm-bindgen = ["futures-timer/wasm-bindgen", "instant/wasm-bindgen", "getrandom/js", "libp2p-swarm/wasm-bindgen"]
 wasm-ext = ["dep:libp2p-wasm-ext"]
 wasm-ext-websocket = ["wasm-ext", "libp2p-wasm-ext?/websocket"]
 webrtc = ["dep:libp2p-webrtc", "libp2p-webrtc?/pem"]

swarm/Cargo.toml

@@ -24,6 +24,8 @@ rand = "0.8"
 smallvec = "1.6.1"
 thiserror = "1.0"
 void = "1"
+wasm-bindgen-futures = { version = "0.4.33", optional = true }
+getrandom = { version = "0.2.3", features = ["js"], optional = true } # Explicit dependency to be used in `wasm-bindgen` feature
 
 [target.'cfg(not(any(target_os = "emscripten", target_os = "wasi", target_os = "unknown")))'.dependencies]
 async-std = { version = "1.6.2", optional = true }
@@ -33,6 +35,7 @@ tokio = { version = "1.15", features = ["rt"], optional = true }
 macros = ["dep:libp2p-swarm-derive"]
 tokio = ["dep:tokio"]
 async-std = ["dep:async-std"]
+wasm-bindgen = ["dep:wasm-bindgen-futures", "dep:getrandom"]
 
 [dev-dependencies]
 async-std = { version = "1.6.2", features = ["attributes"] }

swarm/src/executor.rs

@@ -59,3 +59,14 @@ impl Executor for AsyncStdExecutor {
         let _ = async_std::task::spawn(future);
     }
 }
+
+#[cfg(feature = "wasm-bindgen")]
+#[derive(Default, Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct WasmBindgenExecutor;
+
+#[cfg(feature = "wasm-bindgen")]
+impl Executor for WasmBindgenExecutor {
+    fn exec(&self, future: Pin<Box<dyn Future<Output = ()> + Send>>) {
+        wasm_bindgen_futures::spawn_local(future)
+    }
+}

swarm/src/lib.rs

@@ -420,6 +420,29 @@ where
         builder.build()
     }
 
+    /// Builds a new `Swarm` with a wasm executor.
+    /// Background tasks will be executed by the browser on the next micro-tick.
+    ///
+    /// Spawning a task is similar too:
+    /// ```typescript
+    /// function spawn(task: () => Promise<void>) {
+    ///     task()
+    /// }
+    /// ```
+    #[cfg(feature = "wasm-bindgen")]
+    pub fn with_wasm_executor(
+        transport: transport::Boxed<(PeerId, StreamMuxerBox)>,
+        behaviour: TBehaviour,
+        local_peer_id: PeerId,
+    ) -> Self {
+        Self::with_executor(
+            transport,
+            behaviour,
+            local_peer_id,
+            crate::executor::WasmBindgenExecutor,
+        )
+    }
+
     /// Builds a new `Swarm` without an executor, instead using the current task.
     ///
     /// ## ⚠️  Performance warning