session-ios/SignalUtilitiesKit/OWSOutgoingNullMessage.m

//
//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
//

#import "OWSOutgoingNullMessage.h"
#import "OWSVerificationStateSyncMessage.h"
#import "TSContactThread.h"
#import <SessionProtocolKit/Cryptography.h>
#import <SessionProtocolKit/NSDate+OWS.h>
#import <SignalUtilitiesKit/SignalUtilitiesKit-Swift.h>

NS_ASSUME_NONNULL_BEGIN

@interface OWSOutgoingNullMessage ()

@property (nonatomic, readonly) OWSVerificationStateSyncMessage *verificationStateSyncMessage;

@end

#pragma mark -

@implementation OWSOutgoingNullMessage

- (instancetype)initWithContactThread:(TSContactThread *)contactThread
         verificationStateSyncMessage:(OWSVerificationStateSyncMessage *)verificationStateSyncMessage
{
    // MJK TODO - remove senderTimestamp
    self = [super initOutgoingMessageWithTimestamp:[NSDate ows_millisecondTimeStamp]
                                          inThread:contactThread
                                       messageBody:nil
                                     attachmentIds:[NSMutableArray new]
                                  expiresInSeconds:0
                                   expireStartedAt:0
                                    isVoiceMessage:NO
                                  groupMetaMessage:TSGroupMetaMessageUnspecified
                                     quotedMessage:nil
                                      contactShare:nil
                                       linkPreview:nil];
    if (!self) {
        return self;
    }
    
    _verificationStateSyncMessage = verificationStateSyncMessage;
    
    return self;
}

#pragma mark - override TSOutgoingMessage

- (nullable NSData *)buildPlainTextData:(SignalRecipient *)recipient
{
    SSKProtoNullMessageBuilder *nullMessageBuilder = [SSKProtoNullMessage builder];

    NSUInteger contentLength;
    if (self.verificationStateSyncMessage != nil) {
        contentLength = self.verificationStateSyncMessage.unpaddedVerifiedLength;

        OWSAssertDebug(self.verificationStateSyncMessage.paddingBytesLength > 0);

        // We add the same amount of padding in the VerificationStateSync message and it's coresponding NullMessage so that
        // the sync message is indistinguishable from an outgoing Sent transcript corresponding to the NullMessage. We pad
        // the NullMessage so as to obscure it's content. The sync message (like all sync messages) will be *additionally*
        // padded by the superclass while being sent. The end result is we send a NullMessage of a non-distinct size, and a
        // verification sync which is ~1-512 bytes larger then that.
        contentLength += self.verificationStateSyncMessage.paddingBytesLength;
    } else {
        contentLength = arc4random_uniform(512);
    }

    OWSAssertDebug(contentLength > 0);

    nullMessageBuilder.padding = [Cryptography generateRandomBytes:contentLength];

    NSError *error;
    SSKProtoNullMessage *_Nullable nullMessage = [nullMessageBuilder buildAndReturnError:&error];
    if (error != nil || nullMessage == nil) {
        OWSFailDebug(@"Couldn't build protobuf due to error: %@.", error);
        return nil;
    }

    SSKProtoContentBuilder *contentBuilder = [SSKProtoContent builder];
    contentBuilder.nullMessage = nullMessage;

    NSData *_Nullable contentData = [contentBuilder buildSerializedDataAndReturnError:&error];
    if (error != nil || contentData == nil) {
        OWSFailDebug(@"Couldn't serialize protobuf due to error: %@.", error);
        return nil;
    }

    return contentData;
}

- (uint)ttl { return (uint)[LKTTLUtilities getTTLFor:LKMessageTypeEphemeral]; }

- (BOOL)shouldSyncTranscript
{
    return NO;
}

- (BOOL)shouldBeSaved
{
    return NO;
}

@end

NS_ASSUME_NONNULL_END