[feat] Add NetworkManager:isConnected() (#3593)

This enables connecting to calibre and FTP without Internet connectivity.

frontend/apps/cloudstorage/cloudstorage.lua

@@ -102,13 +102,17 @@ end
 function CloudStorage:openCloudServer(url)
     local tbl
     local NetworkMgr = require("ui/network/manager")
-    if not NetworkMgr:isOnline() then
-        NetworkMgr:promptWifiOn()
-        return
-    end
     if self.type == "dropbox" then
+        if not NetworkMgr:isOnline() then
+            NetworkMgr:promptWifiOn()
+            return
+        end
         tbl = DropBox:run(url, self.password)
     elseif self.type == "ftp" then
+        if not NetworkMgr:isConnected() then
+            NetworkMgr:promptWifiOn()
+            return
+        end
         tbl = Ftp:run(self.address, self.username, self.password, url)
     end
     if tbl and #tbl > 0 then

frontend/ui/network/manager.lua

@@ -60,6 +60,15 @@ function NetworkMgr:promptWifiOff(complete_callback)
     })
 end
 
+function NetworkMgr:isConnected()
+    if Device:isAndroid() then
+        return self:isWifiOn()
+    else
+        -- `-c1` try only once; `-w2` wait 2 seconds
+        return os.execute([[ping -c1 -w2 $(/sbin/route -n | awk '$4 == "UG" {print $2}')]])
+    end
+end
+
 function NetworkMgr:isOnline()
     local socket = require("socket")
     -- Microsoft uses `dns.msftncsi.com` for Windows, see

plugins/calibrecompanion.koplugin/main.lua

@@ -144,7 +144,7 @@ function CalibreCompanion:connect()
         else
             self:setInboxDir(host, port)
         end
-    elseif not NetworkMgr:isOnline() then
+    elseif not NetworkMgr:isConnected() then
         NetworkMgr:promptWifiOn()
     else
         DEBUG("cannot connect to calibre server")