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MORENA: A Middleware for Programming
NFC-enabled Android Applications as
Distributed Object-Oriented Programs
Andoni Lombide Carreton
Kevin Pinte
Wolfgang De Meuter

ACM/IFIP/USENIX 13th International Conference on Middleware 2012
December 5 2012
Montreal, Canada

Monday 28 January 13

RFID in Android

• NFC (touch range).
NdefMessage: {
• Callback on activities ,
to detect RFID tags
with subscribed MIME- , NdefRecord
type in memory. byte array
}
• File access abstraction

read write


Drawbacks of the Android NFC API

• Manual failure handling (and NFC causes A LOT of failures because of its
hardware characteristics).

• Blocking communication (Android documentation recommends to use a
separate thread for many RFID operations).

• Manual data conversion

• Tight coupling with activity-based architecture


Lessons Learnt from Previous Ambient-Oriented
Programming Research

• Using objects as ﬁrst class software representations for RFID-tagged “things”
is a nice abstraction.

• These objects can be directly stored in the RFID tags’ memory to minimize
data conversion.

• Event-driven discovery (fortunately built-in into Android).

• Asynchronous reads and writes.


Middleware Architecture

Application

Thing level One middleware
for Android 4.0
Tag level or higher

Android


Evaluation: WiFi Sharing Application


Things

From now on, we don’t
public class WifiConfig extends Thing { have to worry about the
public String ssid_;
activity anymore.
public String key_;

public WifiConfig(ThingActivity<WifiConfig> activity, String ssid, String key) {
super(activity);
ssid_ = ssid;
key_ = key;
}

public boolean connect(WifiManager wm) {
// Connect to ssid_ with password key_
};
Supported serialization:
}
- JSON-serializable ﬁelds.
- Skipping transient ﬁelds.
- Deep serialization, no cycles.

Initializing Things
As soon as an empty
tag is detected
@Override
public void whenDiscovered(EmptyRecord empty) {
empty.initialize(
myWifiThing,
new ThingSavedListener<WifiConfig>() {
@Override
public void signal(WifiConfig thing) {
toast("WiFi joiner created!");
}
},
new ThingSaveFailedListener() {
@Override
public void signal() {
toast("Creating WiFi joiner failed, try again.");
}
});
}

Discovering and Reading Things

As soon as a WifiConfig
tag is detected
@Override
public void whenDiscovered(WifiConfig wc) {
toast("Joining Wifi network " + wc.ssid_);
wc.connect();
}
Contains cached fields for
synchronous access.
Physical reads must be
asynchronous.


Saving Modiﬁed Things

myWifiConfig.ssid_ = "MyNewWifiName";
myWifiConfig.key_ = "MyNewWifiPassword";

myWifiConfig.saveAsync(
new ThingSavedListener<WifiConfig>() {
@Override
public void signal(WifiConfig wc) {
toast("WiFi joiner saved!");
}
},
new ThingSaveFailedListener() {
@Override
public void signal() {
toast("Saving WiFi joiner failed, try again.");
}
});


Broadcasting Things to Other Phones

Will trigger whenDiscovered on the
receiving phone with the broadcasted thing

myWifiConfig.broadcast(
new ThingBroadcastSuccessListener<WifiConfig>() {
@Override
toast("WiFi joiner shared!");
}
},
new ThingBroadcastFailedListener<WifiConfig>() {
@Override
toast("Failed to share WiFi joiner, try again.");
}
});


Detecting RFID Tags

new MyTagDiscoverer(this,
THING_TYPE,
new NdefMessageToStringConverter(),
new StringToNdefMessageConverter());

private class MyTagDiscoverer extends TagDiscoverer {
@Override
public void onTagDetected(TagReference tagReference) {
readTagAndUpdateUI(tagReference);
}

@Override
public void onTagRedetected(TagReference tagReference) {
}
}


The Tag Reference Abstraction


Reading RFID Tags

tagReference.read(
new TagReadListener() {
@Override
public void signal(TagReference tagReference) {
// tagReference.getCachedData()
}
},
new TagReadFailedListener() {
@Override
// Deal with failure
}
});


Writing RFID Tags

tagReference.write(
toWrite,
new TagWrittenListener() {
@Override
// Handle write success
}
},
new TagWriteFailedListener() {
@Override
// Deal with failure
}
});


Fine-grained Filtering

private class MyTagDiscoverer extends TagDiscoverer {
@Override
public void onTagDetected(TagReference tagReference) {
}

@Override
public void onTagRedetected(TagReference tagReference) {
}

@Override
public boolean checkCondition(TagReference tagReference) {
// Can be used to apply a predicate
// on tagReference.getCachedData()
}
}


Conclusion

• Event-driven discovery.

• Non-blocking communication:

• Things: cached copy, asynchronous saving of cached data.

• TagReferences: ﬁrst class references to RFID tags oﬀering asynchronous
reads and writes.

• Automatic data conversion

• Looser coupling from activity-based architecture

• Data structures over several tags, stronger consistency guarantees?


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