Question

Hi I am trying to create a packet that I want to send over the network to a server, I have pretty much got the packet sorted however its missing a length identifier which I need to calculate at the end of my method and add into the packet.

The packet structure is like this

• leading value identifier (UInt16)
• content size (UInt32)
• packet Content (string)

currently my method looks something like this

- (NSMutableData *) addRegCode
{
    //Supply some default string for testing
    NSString *regCode = [[NSString alloc] initWithString:@"abcd1"];
    //create NSData object
    NSData *registrationCodeData = [regCode dataUsingEncoding:NSUTF8StringEncoding];

    NSMutableData * RegistrationCodeMutableData = [[NSMutableData alloc] init]; //send this object
    //create leading value
    UInt16 leadingValue = 8;
    NSData * leadingValueData = [[NSData alloc] initWithBytes:&leadingValue length:sizeof(leadingValue)];

    //append data to mutableData
    [RegistrationCodeMutableData appendData:leadingValueData];
    [RegistrationCodeMutableData appendData:registrationCodeData];

    return RegistrationCodeMutableData;
}

what I would like to know is how to calculate the size of registrationCodeData and then add it between where I append leadingValueData & registrationCodeData

I think I have to be using dataWithBytes:length: but I’m not 100% sure of how to use this

Answer 1

this should do it.

NSUInteger size = [registrationCodeData length];
NSData *sizeData = [NSData dataWithBytes:&size length:sizeof(size)];
[RegistrationCodeMutableData appendData:leadingValueData];
[RegistrationCodeMutableData appendData:sizeData];
[RegistrationCodeMutableData appendData:registrationCodeData];

also of note using capital letters to start variable names is a little atypical and can be confusing to read!