(O)Authenticated rest interaction in Android

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Thanks for coming!

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About me Federico Paolinelli [email protected] mytechaddiction.blogspot.com @fedepaol plus.google.com/+FedericoPaolinelli

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Let’s talk about REST interaction

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Resources….

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… you want to access

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… you want to access http(s)

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Http call (*) URL url = new URL(“https://api.github.com/users/fedepaol/events");! ! HttpURLConnection conn = (HttpURLConnection) url.openConnection();! ! InputStream in = new BufferedInputStream(conn.getInputStream());! // do whatever you want with the stream! conn.disconnect();! (*)Try/Catches not included

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What are our goals?

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Making our apps work like magic

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… or at least • providing a good user experience • being efﬁcient in terms of power / bandwidth

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DON’TS (it would be better not to…)

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Antipatterns • Performing the call on the ui thread

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Antipatterns • Performing the call on the ui thread • Hosting the thread that perform the call in the activity (or fragment)

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Antipatterns • Performing the call on the ui thread • Hosting the thread that perform the call in the activity (or fragment) • Storing the results (only) in memory

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RULE #1 Decouple the UI from the http call

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Decoupling the call from the UI • The activity might be killed

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Decoupling the call from the UI • The activity might be killed • Conﬁg changes handling

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Decoupling the call from the UI • The activity might be killed • Conﬁg changes handling • Can’t schedule requests

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Decoupling the call from the UI • The activity might be killed • Conﬁg changes handling • Can’t schedule requests • Harder to test

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So where am I supposed to perform the call?

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Service A facility for the application to tell the system about something it wants to be doing in the background (even when the user is not directly interacting with the application)

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How to tell the service to initiate a request Activity Service startService() Intent onStartCommand()

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How to tell the service to initiate a request (2) Activity Service bindService() bind() ServiceInterface onBind()

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CONS PROS Services pros / cons • Can run in background • Can be scheduled • When bound, offers a rich interface • Needs to be shut down • Needs to perform requests in a different thread

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IntentService or how to kill two birds with one stone

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IntentService • Performs the request inside a different thread • Dies when onHandleIntent returns • Queued • Command pattern protected void onHandleIntent(Intent intent) {! String myParameter = intent.getExtras().getString(…);! ! // Handle your request here! }

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Activity Service Request

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Where should I store the result data?

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Where to store the data • Reloading the same data has a cost • Decoupled from the ui • Data can be accessed when offline/prefetched Persistent Storage SQLite Content Provider

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Storage Use Transactions (and yieldIfContededSafely()) ! bulkInsert() with content providers ! Load only New data if the api offers a “since” parameter

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Activity Service Request Storage

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Notify the UI of the result of the request one last step..

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Notify the UI • Local Broadcasts ! ! • Bound Interface (not available with intent services) ! • EventBus (Otto, GreenRobot’s EventBus) ! Intent intent = new Intent(Constants.SERVER_REQUEST_DONE);! intent.putExtra(Constants.REQUEST_ID, mRequestId);! intent.putExtra(Constants.IGNORE_PENDING_ID, mIgnorePending);! LocalBroadcastManager.getInstance(c).sendBroadcast(intent);

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Notify the UI when using ContentProviders • Register observers • CursorLoader gets notiﬁed and reloads the cursor @Override! public Cursor query(Uri uri, String[] projection, String selection,! String[] selectionArgs, String sortOrder) {! // perform the query! cursor.setNotificationUri(getContext().getContentResolver(), uri);! return cursor;! }! ! @Override! public Uri insert(Uri uri, ContentValues values) {! // ..! getContext().getContentResolver().notifyChange(insertedId, null);! // ..! }!

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Activity Service Request Storage Notify Update

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When?

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When to fetch the data React to user input ! Scheduled prefetch (using AlarmManager) ! Push from the server ( GCM)

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Big cookie approach CommonsCreative: http://www.flickr.com/photos/shellewill79/5333263261/

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Big cookie approach • The cell radio is one of the biggest battery drains on the phone • It takes up to 2 seconds to turn the radio on • Every time you transfer data, the radio is powered on for nearly 30 seconds

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Off the shelf solutions

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SyncAdapters • Designed to be used together with Content Providers and Account Authenticator • Native retry mechanism and exponential backoff • Check network availability • Sync with other apps • (Were) a bit tricky to setup http://developer.android.com/training/sync-adapters/

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Robospice • Service decouples the interaction from the ui • Very high level, strongly typed • A lot of features such as caching, json parsing, prioritizing • Retry policy • Very active development https://github.com/octo-online/robospice

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Others.. • Volley • DataDroid (https://github.com/foxykeep/datadroid) • Ion (https://github.com/koush/ion) • Retroﬁt (http://square.github.io/retroﬁt)

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PostmanLib CommonsCreative: http://www.flickr.com/photos/workfromtheheart/5881426342/

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PostmanLib • Allows asynchronous requests • Built on top of java scribe library • Tracks the state of pending requests https://github.com/fedepaol/PostmanLib--Rings-Twice--Android

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Implement a RestRequest interface public class PostmanRequest implements RestServerRequest {! @Override! public String getUrl() {! return "https://api.github.com/users/fedepaol/events";! }! ! @Override! public Verb getVerb() {! return Verb.GET;! }! ! @Override! public void onHttpResult(Response result, ! int statusCode, ! RequestExecutor executor,! Context context) throws ResultParseException {! String resultToParse = result.getBody();! // ...! }! } https://github.com/fedepaol/PostmanLib--Rings-Twice--Android

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Send a request and track the result PostmanRequest r = new PostmanRequest();! PostmanRequest r1 = new PostmanRequest();! ServerInteractionHelper.getInstance(this).sendRestAction(this, "ReqID", r, r1);! ! ! ! ! @Override! protected void onResume() {! mHelper.registerEventListener(this, this);! if (mHelper.isRequestAlreadyPending("ReqID")) {! // notify that a request is still pending, ie action bar spinner! }! }! ! @Override! public void onServerResult(String result, String requestId) {! if ("MyRequestID".equals(requestId)) {! // update the ui! }! https://github.com/fedepaol/PostmanLib--Rings-Twice--Android

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PostmanLib • Can batch / chain requests • Does not provide storage / caching • Does not provide scheduling out of the box • Can get a PendingIntent out of a request to schedule • Requests need to implement Parcelable https://github.com/fedepaol/PostmanLib--Rings-Twice--Android

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PostmanLib UI Helper IntentService(s) sendRestAction() Intent Execute() onServerResult() LocalBroadcast https://github.com/fedepaol/PostmanLib--Rings-Twice--Android

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Yes, but I came here to hear of OAuth

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OAuth • Allows to access resources owned by the user without sharing credentials with the app • Used by nearly all the rest apis • User can revoke the permissions

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OAuth All we need is an Access Token

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Get a client id and a client secret

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OAuth 1.0(a) CommonsCreative: http://www.flickr.com/photos/venndiagram/5331296718 Doesn’t look easy

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OAuth 1.0(a)

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OAuth 1.0(a) - SignPost • Lightweight • Does not wrap http calls • Easy to use ! http://code.google.com/p/oauth-signpost/

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OAuth 2.0

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Java Scribe • Uses HttpUrlConnection under the hood • Comes with a lot of api support included • Supports OAuth 1.0 and OAuth 2.0 • Does not expose the HttpUrlConnection outside https://github.com/fernandezpablo85/scribe-java

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At some point, the user needs to interact with the service …

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How to get the Auth Code use the System Browser ! open a WebView ! use a Custom Activity

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PostmanLib uses Scribe under the hood

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PostmanLib Register an oauth service private void setAuthService() {! OAuthHelper o = OAuthHelper.getInstance();! if (!o.isAlreadyAuthenticated("Facebook", this)) {! StorableServiceBuilder builder = new ! StorableServiceBuilder("Facebook")! .provider(FacebookApi.class)! .apiKey("xxxxxxxx")! .apiSecret("yyyyyyyyyy")! .callback("http://www.yoururl.com/callback", "code")! .scope("publish_actions");! ! o.registerOAuthService(builder, this);! }! } https://github.com/fedepaol/PostmanLib--Rings-Twice--Android

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PostmanLib Obtain the access token OAuthHelper o = OAuthHelper.getInstance();! if (!o.isAlreadyAuthenticated("Facebook", this)) {! o.authenticate(this, "Facebook");! } https://github.com/fedepaol/PostmanLib--Rings-Twice--Android

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PostmanLib Perform the request public class ShareOnFacebookAction implements RestServerRequest {! private static final String url = "https://graph.facebook.com/me/feed";! ! @Override! public String getOAuthSigner() {! return "Facebook";! }! // . . .! } https://github.com/fedepaol/PostmanLib--Rings-Twice--Android

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Thanks Federico Paolinelli @fedepaol [email protected]