Backup domains

lib/getHost.js

@@ -0,0 +1,57 @@
+let availableDomain = 'update.reactnative.cn';
+
+function ping(domain) {
+  return new Promise((resolve, reject) => {
+    const xhr = new XMLHttpRequest();
+    xhr.onreadystatechange = e => {
+      if (xhr.readyState !== 4) {
+        return;
+      }
+      if (xhr.status === 200) {
+        resolve(domain);
+      } else {
+        setTimeout(reject, 5000);
+      }
+    };
+    xhr.open('HEAD', `https://${domain}`);
+    xhr.send();
+    xhr.timeout = 5000;
+    xhr.ontimeout = reject;
+  });
+}
+
+function logger(...args) {
+  // console.warn('pushy', ...args);
+}
+
+export async function tryBackupDomains() {
+  try {
+    await ping(availableDomain);
+    logger('main domain ok');
+    return;
+  } catch (e) {
+    logger('main domain failed');
+  }
+  let backupDomains = [];
+  try {
+    const resp = await fetch(
+      'https://cdn.jsdelivr.net/gh/reactnativecn/react-native-pushy@master/domains.json',
+    );
+    backupDomains = await resp.json();
+    logger('get remote domains:', backupDomains);
+  } catch (e) {
+    logger('get remote domains failed');
+    return;
+  }
+  const fastestDomain = await Promise.race(backupDomains.map(ping));
+  if (typeof fastestDomain === 'string') {
+    logger(`pick domain: ${fastestDomain}`);
+    availableDomain = fastestDomain;
+  } else {
+    logger('all remote domains failed');
+  }
+}
+
+export default function getHost() {
+  return `https://${availableDomain}/api`;
+}