iOS 11 - How does one read/parse the NDEF Message

I have a bunch of tags that are URL tags that have the content "http://WEBSITE.com". Let's say WEBSITE is youtube so http://youtube.com. When I scan them on Android etc, it keeps the http or https.

I'm trying to scan these same tags using the Core NFC framework. I scan them and I get a bunch of bytes that I convert using NSSString initWithData with UTF8 Encoding. I get back \^Cyoutube.com. I want to get http://youtube.com.

How can I interept the payload to get what I need? If I'm to assume the http in front of the string, how am I supposed to know if it is http or https or even ftp?

Edit 1:

I'm having issues with the below answer code for pure text records. When making a text record for "hello world" I get the following outputs from the console:

2017-06-09 12:45:35.151806-0400 testNFC[2963:190724] Payload string:https://www.enhello world

2017-06-09 12:45:35.154959-0400 testNFC[2963:190724] Payload data:<02656e68 656c6c6f 20776f72 6c64>

To get the string I use

NSString *nfcMessage = [nfcType stringByAppendingString:[[[NSString alloc] initWithData:payload.payload encoding:NSUTF8StringEncoding] substringFromIndex:1]];

nfcType is the return from your function but for the None case I return @"";

I'm expecting to just get hello world.

回答1:

For this, you will first need to make sure you have properly formatted NDEF tags. You can use an Android phone or one of these reader accessories along with an NDEF writing app.

Implement the following methods:

- (NSString *)getType:(NSData *)NDEFData {

    NSString *firstByte = [self getFirstByte:NDEFData];

    if ([firstByte isEqualToString:@"00"]) {
        return @"None";
    } else if ([firstByte isEqualToString:@"01"]) {
        return @"http://www.";
    } else if ([firstByte isEqualToString:@"02"]) {
        return @"https://www.";
    } else if ([firstByte isEqualToString:@"03"]) {
        return @"http://";
    } else if ([firstByte isEqualToString:@"04"]) {
        return @"https://";
    } else if ([firstByte isEqualToString:@"05"]) {
        return @"tel:";
    } else if ([firstByte isEqualToString:@"06"]) {
        return @"mailto:";
    } else if ([firstByte isEqualToString:@"07"]) {
        return @"ftp://anonymous:anonymous@";
    } else if ([firstByte isEqualToString:@"08"]) {
        return @"ftp://ftp.";
    } else if ([firstByte isEqualToString:@"09"]) {
        return @"ftps://";
    } else if ([firstByte isEqualToString:@"0A"]) {
        return @"sftp://";
    } else if ([firstByte isEqualToString:@"0B"]) {
        return @"smb://";
    } else if ([firstByte isEqualToString:@"0C"]) {
        return @"nfs://";
    } else if ([firstByte isEqualToString:@"0D"]) {
        return @"ftp://";
    } else if ([firstByte isEqualToString:@"0E"]) {
        return @"dav://";
    } else if ([firstByte isEqualToString:@"0F"]) {
        return @"news:";
    } else if ([firstByte isEqualToString:@"10"]) {
        return @"telnet://";
    } else if ([firstByte isEqualToString:@"11"]) {
        return @"imap:";
    } else if ([firstByte isEqualToString:@"12"]) {
        return @"rtsp://";
    } else if ([firstByte isEqualToString:@"13"]) {
        return @"urn:";
    } else if ([firstByte isEqualToString:@"14"]) {
        return @"pop:";
    } else if ([firstByte isEqualToString:@"15"]) {
        return @"sip:";
    } else if ([firstByte isEqualToString:@"16"]) {
        return @"sips:";
    } else if ([firstByte isEqualToString:@"17"]) {
        return @"tftp:";
    } else if ([firstByte isEqualToString:@"18"]) {
        return @"btspp://";
    } else if ([firstByte isEqualToString:@"19"]) {
        return @"btl2cap://";
    } else if ([firstByte isEqualToString:@"1A"]) {
        return @"btgoep://";
    } else if ([firstByte isEqualToString:@"1B"]) {
        return @"tcpobex://";
    } else if ([firstByte isEqualToString:@"1C"]) {
        return @"irdaobex://";
    } else if ([firstByte isEqualToString:@"1D"]) {
        return @"file://";
    } else if ([firstByte isEqualToString:@"1E"]) {
        return @"urn:epc:id:";
    } else if ([firstByte isEqualToString:@"1F"]) {
        return @"urn:epc:tag:";
    } else if ([firstByte isEqualToString:@"20"]) {
        return @"urn:epc:pat:";
    } else if ([firstByte isEqualToString:@"21"]) {
        return @"urn:epc:raw:";
    } else if ([firstByte isEqualToString:@"22"]) {
        return @"urn:epc:";
    } else if ([firstByte isEqualToString:@"23"]) {
        return @"urn:nfc:";
    }

    return @"";

}

/*!
* gets the the NDEF content
*/
- (NSString *)getNDEFContent:(NSData *)data {
     NSString *dataString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
     return [dataString substringFromIndex:2];
}

/*!
 * gets the first byte of the input NSData
 */
- (NSString *)getFirstByte:(NSData *)data {
     return [[self dataToHexString:data] substringToIndex:2];
}

/*!
 * transforms NSData to NSString
 */
- (NSString *)dataToHexString:(NSData *)data;
{
    // get the length of the data
    NSUInteger bytesCount = data.length;
    if (bytesCount) {
        // string with all the Hex characters
        const char *hexChars = "0123456789ABCDEF";
        // put bytes into an array and initialize the response array
        const unsigned char *dataBuffer = data.bytes;
        char *chars = malloc(sizeof(char) * (bytesCount * 2 + 1));
        char *s = chars;
        // go through data bytes making the transformations so a hex will literally translate to a string, so for example 0x0A will translate to "0A"
        for (unsigned i = 0; i < bytesCount; ++i) {
            // get hexChars character at binary AND between the current byte and 0xF0 bitwise to the right by 4 index and assign it to the current chars pointer
            *s++ = hexChars[((*dataBuffer & 0xF0) >> 4)];
            // get hexChars character at binary AND between the current byte and 0x0F index and assign it to the current chars pointer
            *s++ = hexChars[(*dataBuffer & 0x0F)];
            dataBuffer++;
        }
        *s = '\0';
        // chars to string
        NSString *hexString = [NSString stringWithUTF8String:chars];
        free(chars);
        return hexString;
    }
    return @"";
}

And call the getType method:

[self getType:yourNDEFPayloadNSData]

I'm assuming that all the methods are in the same class and,
that the payload NSData is NDEF compliant, but I modeled the code based on the NFCNDEFPayload payload

回答2:

NFC NDEF message payload is much more complex than you expected. But CoreNFC does not support parsing NFC NDEF message payload. I created an open source parser VYNFCKit to parse payload. Example projects are available in both Objective-C and Swift. Check my tutorial https://medium.com/@vinceyuan/reading-and-parsing-nfc-tag-on-ios-11-60f4bc7a11ea

回答3:

Regarding your EDIT1: You are using the wrong Record Type. You need to write a "Text Record", not a "URI Record". If you have an Android Phone at hand, you could use tools like "NFC TagWriter by NFC" to write the correct record. It might not be important for your use case, but think of interopability with Android Phones, resp. other apps. They would try to open "https://www.enhello world" instead of showing "Hello World", using EN encoding as a Text String.