WebAPI/WebNFC: Difference between revisions

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System level apps declare an additional certified system message permissions, as it fires the nfc-ndef-discovered WebActivities to applications that declare NFC NDEF support:
System level apps declare an additional certified system message permissions, as it fires the nfc-ndef-discovered WebActivities to applications that declare NFC NDEF support:


Example:
Application Usage Example:


   "permissions": {
   "permissions": {

Revision as of 09:48, 24 January 2014

Introduction

Current Status (As to Firefox OS v1.4)

  • Gecko meta bug, bug 860906
  • Gaia meta bug, bug 933640
  • Gonk
    • Use a native daemon nfcd which links to native NFC library. nfcd github
  • Hardware
    • Using Nexus-4, which uses Broadcom NFC chipset with libnfc-nci library.

Security Review (By Paul Theriault)

Contributers

  • Gecko Engineers: Markus Neubrand, Arno Puder, Garner Lee, Siddartha Pothapragada, Philipp von Weitershausen, Yoshi Huang, Dimi Lee.

Roadmap

First iteration: NDEF (Firefox OS v1.3)

  • Technologies:
    • Focus on NDEF standard only for now
    • Others (e.g. proprietary MIFARE) to be investigated later.
  • Capabilities:
    • Read/write NDEF records on tags
    • P2P mode. bug 933136
  • Implementation:
    • See bug 674741
    • NDEF-only API is available on MozNFCTag object.
    • Discovered NDEF tags are automatically parsed and dispatched to content in the "nfc-manager-tech-discovered" system message.
    • 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 WebActivity.
  • Gonk
  • Hardware
    • Using Nexus-4, which uses Broadcom NFC chipset with libnfc-nci library.

Second iteration: Handover, Secure Element (Firefox OS v1.4)

Proposed API

MozNFCTag.webidl

 enum NFCTechType {
   "NFC_A",
   "NFC_B",
   "NFC_ISO_DEP",
   "NFC_F",
   "NFC_V",
   "NDEF",
   "NDEF_FORMATABLE",
   "MIFARE_CLASSIC",
   "MIFARE_ULTRALIGHT",
   "NFC_BARCODE",
   "P2P",
   "UNKNOWN_TECH"
 };

 interface MozNFCTag : EventTarget {
   DOMRequest getDetailsNDEF();
   DOMRequest readNDEF();
   DOMRequest writeNDEF(sequence<MozNdefRecord> records);
   DOMRequest makeReadOnlyNDEF();

   DOMRequest connect(NFCTechType techType);
   DOMRequest close();
 };

MozNFCPeer.webidl

sendNDEF does a P2P send of an NDEF formatted message to another NFC enabled device. NFCPeer will also handle send a generic blob in handover requests where a NDEF formatted "handover" message will conditionally trigger pairing with another device over an available Bluetooth or Wifi connection. 

 interface MozNFCPeer : EventTarget {
   DOMRequest sendNDEF(sequence<MozNdefRecord> records);
   DOMRequest sendFile(Blob blob);
 };

TODO: sendFile is still being implemented in bug 933093 (As of 2013.12.20)

MozNdefRecord.webidl

NDEF records contain a bunch of metadata and a payload that is exposed as a Uint8Array. 

 interface NdefRecord {
   /**
    * Type Name Field (3-bits) - Specifies the NDEF record type in general.
    * tnf_empty: 0x00
    * tnf_well_known: 0x01
    * tnf_mime_media: 0x02
    * tnf_absolute_uri: 0x03
    * tnf_external type: 0x04
    * tnf_unknown: 0x05
    * tnf_unchanged: 0x06
    * tnf_reserved: 0x07
    */
   readonly attribute octet tnf;

   /**
    * type - Describes the content of the payload. This can be a mime type.
    */
   readonly attribute Uint8Array type;

   /**
    * id - Identifer is application dependent.
    */
   readonly attribute Uint8Array id;

   /**
    * payload - Binary data blob. The meaning of this field is application dependent.
    */
   readonly attribute Uint8Array payload;
 };

MozNfc.webidl

 interface mozNfc {
    /* Get the NFCTag */
    DOMRequest getNFCTag(DOMString sessionToken);

    /* Get the NFCPeer for Peer to Peer interactions */
    DOMRequest getNFCPeer(DOMString sessionToken);

   /**
    * API to update chrome about the top-most (visible)
    * application's manifest URL that is capable of
    * handling peer notifications.
    *
    * Users of this API should have valid permissions 'nfc-manager'
    * and 'nfc-write'
    */
   DOMRequest checkP2PRegistration(DOMString manifestUrl);

   /* Sets a callback to notifiy when NDEF Push message communication is available for use. */
   attribute EventHandler onpeerready();
   attribute EventHandler onpeerlost();

   /* Foreground dispatch allows the app, if in the foreground, to get routed all
      NFC messages. Useful for applications that write NFC tags. Privilaged API. */
   attribute EventHandler onforegrounddispatch();
 };

Check bug 933136, or onpeerready for how onpeerready is called.

foreground dispatch is still being implemented, bug 937430

Receiving NDEF messages, via MozActivity

Setup an Activity handler for incoming NDEF messages. The web activity chooser UI will route the messsage to the user selected application if there is more than one match. Currently, only NDEF is supported, although individual nfc tags can actually be compatible with multiple legacy and proprietary technology types.

Applications that do not have "nfc" read or write permissions can still get NDEF events via activities, and act on the data. The raw NDEF data is included with the activity, should the application wish to process any special properties of more complex NDEF data structures.

If the NFC NDEF tag type is well known, such as URIs, the activity will be delievered with some extra fields already parsed.

In the application manifest, declare the following in the activities block to get nfc ndef discovered events. 

 "nfc-ndef-discovered": {
   "filters": {
     "type": "uri",
     "uri": { "required":true, "regexp":"/^https?:.{1,16384}$/i" }
   }
 },

Then implement an activity handler in the application: 

 navigator.mozSetMessageHandler('activity', NfcActivityHandler);
 
 function NfcActivityHandler(activity) {
   var activityName = activity.source.name;
   var data = activity.source.data;
 
   switch (activityName) {
     case 'nfc-ndef-discovered':
       console.log('nfc ndef message records(s): ' + JSON.stringify(data.records));
       console.log('Session Token: ' + JSON.stringify(data.sessionToken));
       console.log('Technology Detected: ' + JSON.stringify(data.tech));
       handleNdefDiscovered(data);
       break;
 }

TODO: Add a diagram to illustrate how tag is dispatched.

Application Permissions

NFC API can be used only by certified app.

To use general reading NDEF API, at least nfc-read permission is required. To write NDEF or to use NFCPeer, nfc-write is required.

For those APIs used by the nfc_manager in System app, nfc-manager permission is required, and is available to certified applications only. It must *not* be used in any other application besides System App.

System level apps declare an additional certified system message permissions, as it fires the nfc-ndef-discovered WebActivities to applications that declare NFC NDEF support:

Application Usage Example: 

 "permissions": {
   "nfc": { "access": "readwrite" }
 }

NFC example

NDEF Utilitiy function

MozNdefRecord is a binary format, and the data is packed into Uint8Array fields. In the following examples, we'll just refer to this helper function to convert javascript strings to Uint8Array buffers. 

 var NfcUtil = {
   fromUTF8: function nu_fromUTF8(str) {
     var buf = new Uint8Array(str.length);
     for (var i = 0; i < str.length; i++) {
       buf[i] = str.charCodeAt(i);
     }
     return buf;
   }
 }

NDEF Connect Example

To establish an NFC application session, all NFCTag operations require an initial connect. It also selects the technology to use for subsequent operations until close/disconnect. 

 nfctag = window.navigator.mozNfc.getNFCTag(sessionToken);

 var connectreq = nfctag.connect("NDEF");
 connectreq.onsuccess = function() {
   console.log('Connect success!');
 };
 connectreq.onerror = function() {
   console.log('ERROR: Failed to connect.');
 };

NFC Close Example

Applications should disconnect when done to release resources. TODO: is it called close or disconnect ? 

 var closereq = nfctag.close();
 closereq.onsuccess = function() {
   console.log('NFC tag close success!');
 };
 closereq.onerror = function() {
   console.log('ERROR: Failed to close.');
 };

NDEF Details Example

 var detailreq = nfctag.getDetailsNDEF();
 detailreq.onsuccess = function() {
   console.log('Max NDEF Message Length: ' + detailreq.result.maxNdefMsgLen);
 };
 detailreq.onerror = function() {
   console.log('ERROR: Failed to get NDEF details.');
 };

NDEF Read Example

The array of ndef records should be passed along in the web activity already read, but applications can still directly read the tag. The session token arrives from a MozActiviy. 

 var conn = nfctag.connect("NDEF");
 conn.onsuccess = function() {
   var req = nfctag.readNDEF();
   req.onsuccess = function() {
     var records = req.result.records;
     showRecords(records);
     nfctag.close(); // This is a DOMRequest call, truncated code here.
   };
   req.onerror = function() {
     nfctag.close(); // This is a DOMRequest call, truncated code here.
   };
 };
 
 function showRecords(records) {
   records.forEach(function (record) {
     console.log("Found a " + record.tnf + " record" +
                 " of type " + record.type +
                 " with ID " + record.id +
                 " and payload " + record.payload);
   });
 };

NDEF Write Tag Example

 var tnf     = 1;                                                            // NFC Forum Well Known type
 var type    = new Uint8Array(NfcUtil.fromUTF8("U"));                        // URL type
 var id      = new Uint8Array(NfcUtil.fromUTF8(""));                         // id
 var payload = new Uint8Array(NfcUtil.fromUTF8("\u0000http://mozilla.org")); // URL data
 
 var ndefRecords = new MozNdefRecord(tnf, type, id, payload);
 
 var writereq = nfctag.writeNDEF(ndefRecords);
 writereq.onsuccess = function(e) {
   console.log("Successfully wrote records to tag");
 };
 writereq.onerror = function(e) {
   console.log("Write failed!");
 };

NDEF P2P Push Example

Peer to Peer communications to another NFC enabled device does not need a connect, as it will automatically connect implicitly. It also only supports NDEF, which is a common standard data format across different NFC devices. 

 var tnf     = 1;                                                            // NFC Forum Well Known type
 var type    = new Uint8Array(NfcUtil.fromUTF8("U"));                        // URL type
 var id      = new Uint8Array(NfcUtil.fromUTF8(""));                         // id
 var payload = new Uint8Array(NfcUtil.fromUTF8("\u0000http://mozilla.org")); // URL data
 
 var ndefRecords = new MozNdefRecord(tnf, type, id, payload);
 
 // TODO: UPDATE ME. NFCPeer isn't passed in the onpeerready callback.
 window.navigator.onpeerready = function(nfcpeer) {
   var peerreq = nfcpeer.sendNDEF(ndefRecords); // push NDEF message to other NFC device.
   peerreq.onsuccess = function(e) {
     console.log("Successfully pushed P2P message");
   };
   peerreq.onerror = function(e) {
     console.log("P2P push failed!");
   };
 };

NDEF P2P SendFile Example

In order to send a file, 

 var nfcdom = window.navigator.mozNfc;
 nfcdom.onpeerready = function(event) {
   var nfcPeer = nfcdom.getNFCPeer(event.detail);
   // Below is only an example to illustrate that sendfile accepts 'blob'.
   var fakeBlob = new Blob([], {type: 'image/png'});
   var sendfilereq = nfcPeer.sendFile(fakeBlob);
   sendfilereq.onsuccess = function(e) {
     console.log("Successfully sent file");
   };
   sendfilereq.onerror = function(e) {
     console.log("Send file failed!");
   };
 };

Note: 'blob' that is being sent by nfc gaia applications will be 'handed-over' to bluetooth interface. (Only handover to BT is supported for now, TBD: WiFi is to be supported). Gaia application that uses this API, should have 'nfc-write' permissions

Handover Example

TODO: UPDATE ME There is some example landed in bug 903305, however it will be refactored in bug 933093.

Application Dispatch Order

TBD.

Priority (low is highest):

Declared support levels: 

1) Foreground App with declared type support (NFC writing apps need to be able to hold the screen so it can write the message, privilaged nfc permisisons).
2) Handover Types (BT transfers, WiFi direct connection, etc.)
3) Specific declared Type support

NFC Resouces

Reference

Similar APIs

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