Send an empty group sync when linking devices if no groups exist.

app/src/main/java/org/thoughtcrime/securesms/jobs/MultiDeviceContactUpdateJob.java

@@ -244,8 +244,8 @@ public class MultiDeviceContactUpdateJob extends BaseJob {
 
   @Override
   public boolean onShouldRetry(@NonNull Exception exception) {
-    if (exception instanceof PushNetworkException) return true;
-    return false;
+    return exception instanceof PushNetworkException ||
+           exception instanceof NetworkException;
   }
 
   @Override

app/src/main/java/org/thoughtcrime/securesms/jobs/MultiDeviceGroupUpdateJob.java

@@ -30,6 +30,7 @@ import org.whispersystems.signalservice.api.messages.multidevice.SignalServiceSy
 import org.whispersystems.signalservice.api.push.SignalServiceAddress;
 import org.whispersystems.signalservice.api.push.exceptions.PushNetworkException;
 
+import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
@@ -128,7 +129,11 @@ public class MultiDeviceGroupUpdateJob extends BaseJob {
                    BlobProvider.getInstance().getStream(context, uri),
                    length);
       } else {
-        Log.w(TAG, "No groups present for sync message...");
+        Log.w(TAG, "No groups present for sync message. Sending an empty update.");
+
+        sendUpdate(ApplicationDependencies.getSignalServiceMessageSender(),
+                   null,
+                   0);
       }
     } finally {
       BlobProvider.getInstance().delete(context, uri);
@@ -149,11 +154,17 @@ public class MultiDeviceGroupUpdateJob extends BaseJob {
   private void sendUpdate(SignalServiceMessageSender messageSender, InputStream stream, long length)
       throws IOException, UntrustedIdentityException
   {
-    SignalServiceAttachmentStream attachmentStream   = SignalServiceAttachment.newStreamBuilder()
-                                                                              .withStream(stream)
-                                                                              .withContentType("application/octet-stream")
-                                                                              .withLength(length)
-                                                                              .build();
+    SignalServiceAttachmentStream attachmentStream;
+
+    if (length > 0) {
+      attachmentStream = SignalServiceAttachment.newStreamBuilder()
+                                                .withStream(stream)
+                                                .withContentType("application/octet-stream")
+                                                .withLength(length)
+                                                .build();
+    } else {
+      attachmentStream = SignalServiceAttachment.emptyStream("application/octet-stream");
+    }
 
     messageSender.sendMessage(SignalServiceSyncMessage.forGroups(attachmentStream),
                               UnidentifiedAccessUtil.getAccessForSync(context));

libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceMessageSender.java

@@ -869,6 +869,7 @@ public class SignalServiceMessageSender {
   private byte[] createMultiDeviceGroupsContent(SignalServiceAttachmentStream groups) throws IOException {
     Content.Builder     container = Content.newBuilder();
     SyncMessage.Builder builder   = createSyncMessageBuilder();
+
     builder.setGroups(SyncMessage.Groups.newBuilder()
                                         .setBlob(createAttachmentPointer(groups)));
 

libsignal/service/src/main/java/org/whispersystems/signalservice/api/messages/SignalServiceAttachment.java

@@ -10,6 +10,7 @@ import org.whispersystems.libsignal.util.guava.Optional;
 import org.whispersystems.signalservice.internal.push.http.CancelationSignal;
 import org.whispersystems.signalservice.internal.push.http.ResumableUploadSpec;
 
+import java.io.ByteArrayInputStream;
 import java.io.InputStream;
 
 public abstract class SignalServiceAttachment {
@@ -39,6 +40,10 @@ public abstract class SignalServiceAttachment {
     return new Builder();
   }
 
+  public static SignalServiceAttachmentStream emptyStream(String contentType) {
+    return new SignalServiceAttachmentStream(new ByteArrayInputStream(new byte[0]), contentType, 0, Optional.absent(), false, false, null, null);
+  }
+
   public static class Builder {
 
     private InputStream             inputStream;