NDEF

NDEF encode and decode library.

Follows Web NFC Spec conventions.

With support for Capability Container and Type 5 wrapper objects.

Encoder / Decoder

The Web NFC spec describes two basic format/class structures when working with NDEF - NDEFMessage and NDEFRecord.

A Message is a wrapper type for a list of records.

Each record represents an object having recordType and data properties (as well as other depending on type).

There are a wide range of "Well Known" record types supported.

Common recordTypes

In most case the data field of the record is an ArrayBuffer or ArrayBufferView (aka Uint8Array). However, some well know types are parsed for the user.

• 'empty'
• 'url' - data is URL string
• 'text'
• 'smart-poster' - data is NDEFMessage call toRecords to iterate or access data directly to parse in application space.
• 'mime' - mediaType contains further information about data
• 'absolute-url' - data is a URL string
• 'unknown'

Example Decoding with CC wrapper

import { CapabilityContainer } from '@johntalton/ndef'

// see st25dv https://github.com/johntalton/st25dv for init
const st25dv = new ST25DVUser(/* ... */)

 // read 64 bytes starting at offset 0
const buffer = await st25dv.readMemory(0, 64)

const cc = CapabilityContainer.decode(buffer)
for(const record of cc.message.records) {
  const { recordType, id, data } = record

  console.log('id:', id)
  console.log('recordType:', recordType)
  if(recordType === 'mime' && record.mediaType === 'application/json') {
    const decoder = new TextDecoder()
    const json = JSON.parse(decoder.decode(data))
  }
  else {
    // do other stuff
  }
}

Example Encoding without CC

import { NDEFMessageEncoder, CONTEXT_ROOT } from '@johntalton/ndef'

const buffer = NDEFMessageEncoder.encode({
  records: [
    {
      recordType: 'url',
      data: 'https://github.com/johntalton/ndef'
    },
    {
      recordType: 'text',
      data: 'NDEF library in JS'
    },
  ]
}, CONTEXT_ROOT, 0)

// do something with buffer ...

Capability Container & Type 5 Tag

Included in this library is an implementation of the CC/T5T wrapper format needed to write NDEF Message onto a device (such as the st25dv)

The CapabilityContainer provides a encode/decode that will account for the TLV (Type Length Value) container as well as the devices CCFile.

CapabilityContainer provides access to permissions for read and write as well as the root NDEFMessage via message.

(This has limited testing beyond above mentioned st25dv device and basic memory layout - feedback welcome :P)