SWIFT: Paste Bytes from NSData to Struct?

Question

I am writing a bluetooth packets protocol for communication between iPhone and a peripheral device. The device will send me some bits, possibly 128 or 256, and the communication protocol I am using will let me access this incoming data as some NSData variable. My question is, Can I take the bytes from NSDATA or directly use the NSData somehow to paste the bytes into a struct with entries that have predefined size? For example, in C, you would have a struct like:

struct CD2_CONFIG_TYPE {
    uint8_t     header;         // '<' or '>' start of a new packet from device or base station
    uint8_t     type;           // 'c' indicates device configuration packet
    uint8_t     devSN[8];       // device serial number 
};

and lets say the data we received is an NSData object that has 8 + 8 + 84 bits, which are the header, type, and devSN, respectively. So if I take these bits (or bytes) and make them a pointer using something like:

// swift code    
fun dataBYtesToPointer(incomingDataPacket: NSData){
         var packetBytes = UnsafePointer<UInt8>(incomingDataPacket.bytes)
    }

Is there any way to copy the pointer to the struct and have the struct variables header, type, and devSN populated properly based on the size allocated to them? In C you would use memcopy and copy that pointer to a struct. So I don't get how to make the struct with predefined sizes like in the example, and I don't know how to fill it with a pointer. Any help would be appreciated.

I think the answer to your question is here. http://stackoverflow.com/questions/25079380/swift-how-add-offset-to-memcpy — user3069232, Feb 23 '16 at 05:13

score 0 · Accepted Answer · answered Feb 23 '16 at 08:45

0

You can think of a C method as shown below:

struct CD2_CONFIG_TYPE* commandFromData(uint8_t * data){

  struct CD2_CONFIG_TYPE* command = (struct CD2_CONFIG_TYPE*)malloc(sizeof(struct CD2_CONFIG_TYPE));

  command->type = data[0];
  command->header = data[1];
  memcpy(command->devSN, &data[2], 8* sizeof(uint8_t));

  return command;

}

You can export this function signature in a .h file and import it into the bridging header so that Swift code can access this.

In your swift code, you can call this as:

let bytes = UnsafePointer<UInt8>(incomingDataPacket.bytes)
commandFromData(bytes)

answered Feb 23 '16 at 08:45

Shripada

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Thank you @Shripada for the answer. I didn't know you could use C code with swift like that. I got it to work, but instead of using 2nd, 3rd, and 4th line of the function you gave me, i just used memcpy(&command, &data, sizeof(command)); and it copies the entire pointer to the struct all at once. I am very thankful for your help. – vusiliyK Feb 23 '16 at 21:54
Glad that it helped. Yes, the way you are copying is also legitimate stuff. – Shripada Feb 24 '16 at 07:00

SWIFT: Paste Bytes from NSData to Struct?

1 Answers1