CODEWITHSUNDEEP
iphoneobjective-cnsstream
Juulie
Juulie

Reputation: 79

How to send integer through NSOutputStream?

So I'm making an iOS app that constantly sends and array of points through NSStreams, but because sometimes the sender writes two arrays before the receiver receives one, I decided to first write the length, then the array data itself, so that the receiver knows how many bytes to process.

sender:

if (_outStream && [_outStream hasSpaceAvailable]){
    const uint8_t *buffer = [data bytes];
    uint64_t length = CFSwapInt64HostToLittle([data length]);
    NSLog(@"Sending bytes with length: %llu", length);
    int er1 = [_outStream write:(const uint8_t *)&length maxLength:sizeof(length)];
    int er2 = [_outStream write:buffer maxLength:length];  
    if (er1 < 0 || er2 < 0) {
        [self _showAlert:@"Failed sending data to peer"];
    }
}

receiver:

case NSStreamEventHasBytesAvailable:
    {
        if (stream == _inStream) {
            uint8_t *b;
            int len = 0;
            len = [_inStream read:b maxLength:8];
            uint64_t dataLength = CFSwapInt64LittleToHost(*b);
            NSLog(@"Received bytes with length: %llu", dataLength);
            if(len < 0) {
                if ([stream streamStatus] != NSStreamStatusAtEnd)
                    [self _showAlert:@"Failed reading data from peer"];
            } else if (len > 0){
                uint8_t bytes[dataLength];
                int length = [_inStream read:bytes maxLength:dataLength];

                [currentDownload appendBytes:bytes length:length]; 
                 id pointsArray = [NSKeyedUnarchiver unarchiveObjectWithData:currentDownload];
                [currentDownload release];
                currentDownload = [[NSMutableData alloc] init];
                if ([pointsArray isKindOfClass:[NSArray class]]) {
                    [drawScene addNewPoint:[[pointsArray objectAtIndex:0] CGPointValue] previousPoint:[[pointsArray objectAtIndex:1] CGPointValue]];
                }

            }
        }
        break;
    }

The problem is that the receiver receives an incorrect integer, hence it reads an incorrect amount of bytes.

Can anyone help me with this?

Upvotes: 3

Views: 982

Answers (1)

Wienke
Wienke

Reputation: 3733

Could it be that when you read the data, you're starting with the introductory bits intended to convey length, rather than starting with the actual data?

For:

[currentDownload appendBytes:bytes length:length];

try substituting something like this:

NSRange rangeLeftover = NSMakeRange(sizeof(uint8_t), [currentDownload length] - sizeof(uint8_t));
NSData *dataLeftover = [currentDownload subdataWithRange:rangeLeftover];
uint8_t bytesLeftover[[dataLeftover length]];
[dataLeftover getBytes:&bytesLeftover length:[dataLeftover length]];
currentDownload = [NSMutableData data]; // clear
[currentDownload appendBytes:bytesLeftover length:[dataLeftover length]];

Upvotes: 1

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