multiplayer works!

src/api/websocket.js

@@ -0,0 +1,48 @@
+export default async function websocket_open(url, handler) {
+  const socket = new WebSocket(url);
+  socket.binaryType = "arraybuffer";
+  let versionCbk = null;
+  socket.addEventListener("message", ({data}) => {
+    if (versionCbk) {
+      versionCbk(data);
+    }
+    handler(data);
+  });
+  await new Promise((resolve, reject) => {
+    const onError = err => reject(err);
+    socket.addEventListener("error", onError);
+    socket.addEventListener("open", () => {
+      socket.removeEventListener("error", onError);
+      resolve();
+    });
+  });
+  await new Promise((resolve, reject) => {
+    const to = setTimeout(() => {
+      versionCbk = null;
+      reject(Error("connection timed out"));
+    }, 5000);
+    versionCbk = data => {
+      clearTimeout(to);
+      const u8 = new Uint8Array(data);
+      if (u8[0] === 0x32) {
+        versionCbk = null;
+        const version = u8[1] | (u8[2] << 8) | (u8[3] << 16) | (u8[4] << 24);
+        if (version === 1) {
+          resolve();
+        } else {
+          reject("server version mismatch");
+        }
+      }
+    };
+  });
+
+  const vers = process.env.VERSION.match(/(\d+)\.(\d+)\.(\d+)/);
+  const clientInfo = new Uint8Array(5);
+  clientInfo[0] = 0x31;
+  clientInfo[1] = parseInt(vers[3]);
+  clientInfo[2] = parseInt(vers[2]);
+  clientInfo[3] = parseInt(vers[1]);
+  clientInfo[4] = 0;
+  socket.send(clientInfo);
+  return socket;
+}