Better handle service unavailable.

app/src/main/java/at/bitfire/davdroid/Constants.java

@@ -37,5 +37,5 @@ public class Constants {
     public static final Uri serviceUrl = Uri.parse((DEBUG_REMOTE_URL == null) ? "https://api.etesync.com/" : DEBUG_REMOTE_URL);
 
     public static final int DEFAULT_SYNC_INTERVAL = 4 * 3600;  // 4 hours
-
+    public static final long DEFAULT_RETRY_DELAY = 30 * 60; // 30 minutes
 }

app/src/main/java/at/bitfire/davdroid/journalmanager/BaseManager.java

@@ -37,6 +37,8 @@ abstract class BaseManager {
 
         if (!response.isSuccessful()) {
             switch (response.code()) {
+                case HttpURLConnection.HTTP_UNAVAILABLE:
+                    throw new Exceptions.ServiceUnavailableException("Service unavailable", Long.valueOf(response.header("Retry-After", "0")));
                 case HttpURLConnection.HTTP_UNAUTHORIZED:
                     throw new Exceptions.UnauthorizedException("Failed to connect");
                 default:

app/src/main/java/at/bitfire/davdroid/journalmanager/Exceptions.java

@@ -19,8 +19,13 @@ public class Exceptions {
     }
 
     public static class ServiceUnavailableException extends HttpException {
+        public long retryAfter;
         public ServiceUnavailableException(String message) {
+            this(message, 0);
+        }
+        public ServiceUnavailableException(String message, long retryAfter) {
             super(message);
+            this.retryAfter = retryAfter;
         }
     }
 

app/src/main/java/at/bitfire/davdroid/syncadapter/SyncManager.java

@@ -29,6 +29,7 @@ import java.util.logging.Level;
 
 import at.bitfire.davdroid.AccountSettings;
 import at.bitfire.davdroid.App;
+import at.bitfire.davdroid.Constants;
 import at.bitfire.davdroid.GsonHelper;
 import at.bitfire.davdroid.HttpClient;
 import at.bitfire.davdroid.InvalidAccountException;
@@ -183,11 +184,8 @@ abstract public class SyncManager {
             syncResult.stats.numIoExceptions++;
 
         } catch (Exceptions.ServiceUnavailableException e) {
-            Date retryAfter = null; // ((Exceptions.ServiceUnavailableException) e).retryAfter;
-            if (retryAfter != null) {
-                // how many seconds to wait? getTime() returns ms, so divide by 1000
-                // syncResult.delayUntil = (retryAfter.getTime() - new Date().getTime()) / 1000;
-            }
+            long retryAfter = (e.retryAfter > 0) ? e.retryAfter : Constants.DEFAULT_RETRY_DELAY;
+            syncResult.delayUntil = retryAfter;
         } catch (InterruptedException e) {
             return;
         } catch (Exception | OutOfMemoryError e) {