[Desktop] Use fallback mirrors for China users (#2424)

src/utils/networkUtil.ts

@@ -24,3 +24,53 @@ export const checkMirrorReachable = async (mirror: string) => {
     isValidUrl(mirror) && (await electronAPI().NetWork.canAccessUrl(mirror))
   )
 }
+
+/**
+ * Checks if the user is likely in mainland China by:
+ * 1. Checking navigator.language
+ * 2. Testing connectivity to commonly blocked services
+ * 3. Testing latency to China-specific domains
+ */
+export async function isInChina(): Promise<boolean> {
+  // Quick check based on language/locale
+  const isChineseLocale = navigator.language.toLowerCase().startsWith('zh-cn')
+
+  try {
+    // Test connectivity to Google - commonly blocked in China
+    const googleTest = await Promise.race([
+      fetch('https://www.google.com', {
+        mode: 'no-cors',
+        cache: 'no-cache'
+      }),
+      new Promise((_, reject) => setTimeout(() => reject(), 2000))
+    ])
+
+    // If Google is accessible, user is likely not in China
+    if (googleTest) {
+      return false
+    }
+  } catch {
+    // Google is not accessible - potential indicator of being in China
+    if (isChineseLocale) {
+      return true
+    }
+
+    // Additional check - test latency to a reliable Chinese domain
+    try {
+      const start = performance.now()
+      await fetch('https://www.baidu.com', {
+        mode: 'no-cors',
+        cache: 'no-cache'
+      })
+      const latency = performance.now() - start
+
+      // If Baidu responds quickly (<150ms), user is likely in China
+      return latency < 150
+    } catch {
+      // If both tests fail, default to locale check
+      return isChineseLocale
+    }
+  }
+
+  return false
+}