Determine MIME type from NSData?

Question

How would you determine the mime type for an NSData object? I plan to have the user to upload a video/picture from their iPhone and have that file be wrapped in a NSData class.

I was wondering if I can tell the mime type from the NSData. There are only a few answers to this question and the most recent one is from 2010 (4 years ago!). Thanks!

NSData *data; // can be an image or video
NSString *mimeType = [data getMimetype]; // how would I implement getMimeType

Answer 1

Based on ml's answer from a similar post, I've added the mime types determination for NSData:

ObjC:

+ (NSString *)mimeTypeForData:(NSData *)data {
    uint8_t c;
    [data getBytes:&c length:1];

    switch (c) {
        case 0xFF:
            return @"image/jpeg";
            break;
        case 0x89:
            return @"image/png";
            break;
        case 0x47:
            return @"image/gif";
            break;
        case 0x49:
        case 0x4D:
            return @"image/tiff";
            break;
        case 0x25:
            return @"application/pdf";
            break;
        case 0xD0:
            return @"application/vnd";
            break;
        case 0x46:
            return @"text/plain";
            break;
        default:
            return @"application/octet-stream";
    }
    return nil;
}

Swift:

static func mimeType(for data: Data) -> String {

    var b: UInt8 = 0
    data.copyBytes(to: &b, count: 1)

    switch b {
    case 0xFF:
        return "image/jpeg"
    case 0x89:
        return "image/png"
    case 0x47:
        return "image/gif"
    case 0x4D, 0x49:
        return "image/tiff"
    case 0x25:
        return "application/pdf"
    case 0xD0:
        return "application/vnd"
    case 0x46:
        return "text/plain"
    default:
        return "application/octet-stream"
    }
}

This handle main file types only, but you can complete it to fit your needs: all the files signature are available here, just use the same pattern as I did.

PS: all the corresponding mime types are available here