Parse BLE Manufacturer data - Objective-C - ios

Question

I'm working on a custom bluetooth product, the manufacturer has embeded data in the advertisement packet. How do I effectively parse this data so it's usable within an iOS app?
I'm currently grabbing the data from the NSDictionary as follows:
NSData *rawData = [advertisement objectForKey:#"kCBAdvDataManufacturerData"];
The data in the packet is structured like so:
uint8_t compId[2];
uint8_t empty[6];
uint8_t temperature[2];
uint8_t rampRate[2];
uint8_t dutyFactor[2];
uint8_t alarms[2];
uint8_t statusFlag;
uint8_t speedRpm[2];
uint8_t vib[2];
uint8_t deviceTypeId;
uint8_t radioStatus;
uint8_t cycleTimer[2];
uint8_t batteryLevel;
My first thought was to convert it to a string and parse out the data that I need, but this seems slow and really inefficient. There has to be a standard way developers deal with this. I'm still pretty green when it comes to bitwise operators. All the data is formatted in little endian.

Answer 1

Certainly don't convert it to a string, as it isn't one, and you'll have issues with encoding.
Start by checking that the length of the data matches what you're expecting (26 bytes)
Use the bytes method to get a pointer to the data
Add a function or method to combine two bytes into a 16-bit integer. You'll have to find out if those 2-byte fields are signed or unsigned.
Something along these lines:
- (int)getWordFromBuffer:(const unsigned char *)bytes atOffset:(int) offset
{
return (int)bytes[offset] | (bytes[offset+1] << 8);
}
- (NSDictionary *)decodeData:(NSData *)data
{
if (data.length != 26)
{
NSLog(#"wrong length %d instead of 26", data.length);
return nil;
}
const unsigned char *bytes = (unsigned char *)data.bytes;
return
#{
#"compId": #([self getWordFromBuffer:bytes atOffset:0]),
#"temperature": #([self getWordFromBuffer:bytes atOffset:8]),
#"rampRate": #([self getWordFromBuffer:bytes atOffset:10]),
....
};
}