Use SignalAccount class to sync contacts.

// FREEBIE

src/Contacts/SignalAccount.h

@@ -0,0 +1,51 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+NS_ASSUME_NONNULL_BEGIN
+
+@class Contact;
+@class SignalRecipient;
+@class YapDatabaseReadTransaction;
+
+// This class represents a single valid Signal account.
+//
+// * Contacts with multiple signal accounts will correspond to
+//   multiple instances of SignalAccount.
+// * For non-contacts, the contact property will be nil.
+//
+// New instances of SignalAccount for active accounts are
+// created every time we do a contacts intersection (e.g.
+// in response to a change to the device contacts).
+@interface SignalAccount : NSObject
+
+// An E164 value identifying the signal account.
+//
+// This is the key property of this class and it
+// will always be non-null.
+@property (nonatomic, readonly) NSString *recipientId;
+
+// This property is optional and will not be set for
+// non-contact account.
+@property (nonatomic, nullable) Contact *contact;
+
+@property (nonatomic) BOOL hasMultipleAccountContact;
+
+// For contacts with more than one signal account,
+// this is a label for the account.
+@property (nonatomic) NSString *multipleAccountLabelText;
+
+- (instancetype)init NS_UNAVAILABLE;
+
+- (instancetype)initWithSignalRecipient:(SignalRecipient *)signalRecipient;
+
+- (instancetype)initWithRecipientId:(NSString *)recipientId;
+
+// In most cases this should be non-null. This should only
+// be null in the case where the SignalRecipient was
+// deleted before this property was accessed.
+- (nullable SignalRecipient *)signalRecipientWithTransaction:(YapDatabaseReadTransaction *)transaction;
+
+@end
+
+NS_ASSUME_NONNULL_END

src/Contacts/SignalAccount.m

@@ -0,0 +1,51 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import "SignalAccount.h"
+#import "SignalRecipient.h"
+#import "TSStorageManager.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface SignalAccount ()
+
+@property (nonatomic) NSString *recipientId;
+
+@end
+
+#pragma mark -
+
+@implementation SignalAccount
+
+- (instancetype)initWithSignalRecipient:(SignalRecipient *)signalRecipient
+{
+    if (self = [super init]) {
+        OWSAssert(signalRecipient);
+
+        _recipientId = signalRecipient.uniqueId;
+    }
+    return self;
+}
+
+- (instancetype)initWithRecipientId:(NSString *)recipientId
+{
+    if (self = [super init]) {
+        OWSAssert(recipientId.length > 0);
+
+        _recipientId = recipientId;
+    }
+    return self;
+}
+
+- (nullable SignalRecipient *)signalRecipientWithTransaction:(YapDatabaseReadTransaction *)transaction
+{
+    OWSAssert([NSThread isMainThread]);
+    OWSAssert(transaction);
+
+    return [SignalRecipient recipientWithTextSecureIdentifier:self.recipientId withTransaction:transaction];
+}
+
+@end
+
+NS_ASSUME_NONNULL_END

src/Devices/OWSContactsOutputStream.h

@@ -1,14 +1,16 @@
-//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "OWSChunkedOutputStream.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
-@class Contact;
+@class SignalAccount;
 
 @interface OWSContactsOutputStream : OWSChunkedOutputStream
 
-- (void)writeContact:(Contact *)contact;
+- (void)writeSignalAccount:(SignalAccount *)signalAccount;
 
 @end
 

src/Devices/OWSContactsOutputStream.m

@@ -1,28 +1,34 @@
-//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "OWSContactsOutputStream.h"
 #import "Contact.h"
 #import "MIMETypeUtil.h"
 #import "OWSSignalServiceProtos.pb.h"
+#import "SignalAccount.h"
 #import <ProtocolBuffers/CodedOutputStream.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
 @implementation OWSContactsOutputStream
 
-- (void)writeContact:(Contact *)contact
+- (void)writeSignalAccount:(SignalAccount *)signalAccount
 {
+    OWSAssert(signalAccount);
+    OWSAssert(signalAccount.contact);
+    
     OWSSignalServiceProtosContactDetailsBuilder *contactBuilder = [OWSSignalServiceProtosContactDetailsBuilder new];
-    [contactBuilder setName:contact.fullName];
-    [contactBuilder setNumber:contact.textSecureIdentifiers.firstObject];
+    [contactBuilder setName:signalAccount.contact.fullName];
+    [contactBuilder setNumber:signalAccount.recipientId];
 
     NSData *avatarPng;
-    if (contact.image) {
+    if (signalAccount.contact.image) {
         OWSSignalServiceProtosContactDetailsAvatarBuilder *avatarBuilder =
             [OWSSignalServiceProtosContactDetailsAvatarBuilder new];
 
         [avatarBuilder setContentType:OWSMimeTypeImagePng];
-        avatarPng = UIImagePNGRepresentation(contact.image);
+        avatarPng = UIImagePNGRepresentation(signalAccount.contact.image);
         [avatarBuilder setLength:(uint32_t)avatarPng.length];
         [contactBuilder setAvatarBuilder:avatarBuilder];
     }
@@ -33,7 +39,7 @@ NS_ASSUME_NONNULL_BEGIN
     [self.delegateStream writeRawVarint32:contactDataLength];
     [self.delegateStream writeRawData:contactData];
 
-    if (contact.image) {
+    if (signalAccount.contact.image) {
         [self.delegateStream writeRawData:avatarPng];
     }
 }

src/Messages/DeviceSyncing/OWSSyncContactsMessage.m

@@ -8,6 +8,7 @@
 #import "NSDate+millisecondTimeStamp.h"
 #import "OWSContactsOutputStream.h"
 #import "OWSSignalServiceProtos.pb.h"
+#import "SignalAccount.h"
 #import "TSAttachment.h"
 #import "TSAttachmentStream.h"
 
@@ -63,8 +64,8 @@ NS_ASSUME_NONNULL_BEGIN
     [dataOutputStream open];
     OWSContactsOutputStream *contactsOutputStream = [OWSContactsOutputStream streamWithOutputStream:dataOutputStream];
 
-    for (Contact *contact in self.contactsManager.signalContacts) {
-        [contactsOutputStream writeContact:contact];
+    for (SignalAccount *signalAccount in self.contactsManager.signalAccounts) {
+        [contactsOutputStream writeSignalAccount:signalAccount];
     }
 
     [contactsOutputStream flush];

src/Protocols/ContactsManagerProtocol.h

@@ -1,14 +1,16 @@
-//  Created by Frederic Jacobs on 05/12/15.
-//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
-@class PhoneNumber;
 @class Contact;
+@class PhoneNumber;
+@class SignalAccount;
 @class UIImage;
 
 @protocol ContactsManagerProtocol <NSObject>
 
 - (NSString * _Nonnull)displayNameForPhoneIdentifier:(NSString * _Nullable)phoneNumber;
-- (NSArray<Contact *> * _Nonnull)signalContacts;
+- (NSArray<SignalAccount *> * _Nonnull)signalAccounts;
 
 #if TARGET_OS_IPHONE
 - (UIImage * _Nullable)imageForPhoneIdentifier:(NSString * _Nullable)phoneNumber;