Avoid groupsync deadlock - pass in transaction

// FREEBIE

SignalServiceKit/src/Messages/DeviceSyncing/OWSSyncGroupsMessage.h

@@ -1,12 +1,16 @@
-//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "OWSOutgoingSyncMessage.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
+@class YapDatabaseReadTransaction;
+
 @interface OWSSyncGroupsMessage : OWSOutgoingSyncMessage
 
-- (NSData *)buildPlainTextAttachmentData;
+- (NSData *)buildPlainTextAttachmentDataWithTransaction:(YapDatabaseReadTransaction *)transaction;
 
 @end
 

SignalServiceKit/src/Messages/DeviceSyncing/OWSSyncGroupsMessage.m

@@ -40,7 +40,7 @@ NS_ASSUME_NONNULL_BEGIN
     return syncMessageBuilder;
 }
 
-- (NSData *)buildPlainTextAttachmentData
+- (NSData *)buildPlainTextAttachmentDataWithTransaction:(YapDatabaseReadTransaction *)transaction
 {
     // TODO use temp file stream to avoid loading everything into memory at once
     // First though, we need to re-engineer our attachment process to accept streams (encrypting with stream,

SignalServiceKit/src/Messages/OWSMessageManager.m

@@ -615,8 +615,8 @@ NS_ASSUME_NONNULL_BEGIN
                 }];
         } else if (syncMessage.request.type == OWSSignalServiceProtosSyncMessageRequestTypeGroups) {
             OWSSyncGroupsMessage *syncGroupsMessage = [[OWSSyncGroupsMessage alloc] init];
-            DataSource *dataSource =
-                [DataSourceValue dataSourceWithSyncMessage:[syncGroupsMessage buildPlainTextAttachmentData]];
+            DataSource *dataSource = [DataSourceValue
+                dataSourceWithSyncMessage:[syncGroupsMessage buildPlainTextAttachmentDataWithTransaction:transaction]];
             [self.messageSender sendTemporaryAttachmentData:dataSource
                 contentType:OWSMimeTypeApplicationOctetStream
                 inMessage:syncGroupsMessage