WebAPI/WebNFC

First iteration: NDEF

Scope

• Technologies:
  • Focus on NDEF standard only for now
  • Others (e.g. proprietary MIFARE) to be investigated later.
• Capabilities:
  • Read-only for now
  • Tag creation/simulation and two-way communication to be investigated later
• Implementation:
  • NDEF-only API available on navigator.mozNfc.ndef object
  • Discovered NDEF tags are automatically parsed and dispatched to content in the "tagdiscovered" event on navigator.mozNfc.ndef
  • navigator.mozNfc only available to a specific privileged content page (cf. WebTelephony, WebSMS).
  • For now, content is expected to do filtering and dispatching to handlers e.g. via WebIntents/WebActions/postMessage

Proposed API

navigator.mozNfc for now has only one event restricted to NDEF tag discovery. The "ndefdiscovered" NfcNdefEvent will be fired when a new NDEF tag is discovered. The event will contain a reference to the NfcNdefMessage object.

 interface Nfc
 {
   attribute EventListener onndefdiscovered;
 };

 interface NfcNdefEvent : nsIDOMEvent
 {
   readonly attribute NfcNdefMessage message;
 };

An NDEF message is merely a container for NDEF records:

 interface NfcNdefMessage
 {
   readonly attribute NfcNDefRecords[] ndefRecords;  
 };

NDEF records contain a bunch of metadata and a payload that is exposed as both a string and a Typed Array buffer (akin to the response on XMLHttpRequest).

 interface NfcNdefRecord 
 {
   readonly attribute DOMString tnf;
   readonly attribute DOMString type;
   readonly attribute DOMString id;
   readonly attribute DOMString payloadText;
   readonly attribute ArrayBuffer payloadArrayBuffer;  
 };

Example

 navigator.mozNfc.ndef.ontagdiscovered = function (event) {
   console.log("Discovered an NDEF message with " + event.message.records.length + " records.");
   event.message.records.forEach(function (record) {
     console.log("Found a " + record.tnf + " record" +
                 " of type " + record.type +
                 " with ID " + record.id +
                 " and payload " + record.payloadText);
     // record.payloadArrayBuffer is an typed array representation of the payload
     // Could dispatch event.message here to other web apps based on MIME type, URI, etc.
   });
 };

Implementation

• See bug 674741
• Engineers: Markus Neubrand, Arno Puder, Garner Lee, Philipp von Weitershausen