Incorporating Web Services in Mobile Applications

1. Incorporating Web Services in Mobile Applications April 3, 2009 – San Francisco

2. Slides available atwww.aduci.com/web2expo2009sf.ppt

3. Disclaimer Web services and APIs of third parties referenced in this presentation are owned by the third parties and governed by their agreements. Before using any of the APIs or code referenced in this presentation review the terms of use by the third party providing the API. These slides are available under the Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. You can blog, photograph, and share this information with others. Trademarks and brands are the property of their respective owners.

4. Introduction - Convergence • Available APIs are growing daily • Currently 1229 (and growing) APIs registered at Programmable Web • Shifts in Consumer Expectations • Consumers now expect mobile devices to be connected to Internet Sites and Services • Platform Development becoming easier and more standardized • iPhone SDK – Greater than 50,000 registered developers • Android – 5% of smart phone web usage in just three months1 • Seeing extension of enterprise applications to mobile devices • Salesforce.com 1Techcrunch, March 24, 2009, Erick Schonfeld

5. Introduction • Many Web Services and APIs were originally developed with server to server or server to browser in mind, not mobile applications • Mobile platforms have their own set of challenges given: • Bandwidth • Memory and CPU Availability • Storage Capacity • Connectivity Options and Issues • Security • User Interaction and Display Web Service

6. Mobile Integration Challenges

7. API Developer Programs • Is mobile access allowed? • Other considerations: • Call Limitations (# per second, total per hour/day, pricing above) • Caching and Storage of Data • Persistence of Data – Length of time stored • Freshness of Data – Length of time before refreshing • “5.1.5. Unless we have provided you our express written consent in advance, you are not permitted to use Amazon Associates Web Service in connection with any handheld, mobile or mobile phone application.” • From the Amazon Web ServicesTM Customer Agreement • http://aws.amazon.com/agreement/

8. Caching and Storage Limits • Persistence Limitations • Refreshing Requirements • You may otherwise store Amazon Properties generally (other than pricing or availability information) for caching purposes for up to 24 hours. However, you may store the following Amazon Properties for caching purposes for up to 1 month:… • From the Amazon Web Services User Agreement • You must refresh and re-display any Amazon Properties (other than pricing or availability information) at least once every 24 hours or once every month, as applicable, by making a call to AWS and refreshing your Application’s contents immediately after the call. • From the Amazon Web Services User Agreement

9. Application Verification • Certification of your Mobile Application • Some API sets require certification on top of distributor certification • Determine Costs / Timeframe / Effort given a mobile app • Prepare for testing – typically looking for error handling, API abuse • Certification is a positive! • Credibility, validation, marketing • Keeps the neighborhood safe • “If any of your Facebook Platform Applications are client-resident (including on a mobile device), you agree to furnish a copy of such Facebook Platform Applications and any supporting documentation upon request for the purpose of verifying your compliance with this Agreement; and …” • From the Facebook Developer Terms of Service

10. Mobile Techniques

11. Authentication vs. Authorization • The Difference Authentication from the API provider – API Key Authorization from the user – authToken • Session Key • By providing combination of API Key and authToken can then receive the session key • What is the shelf life of the session key • Authorization will commonly affect user’s experience on mobile • eBay authentication and authorization screens

12. Last.fm - Sample Flow • http://www.lastfm.com/api/mobileauth • Get an API key • Request auth – auth.getMobileSession • Inputs: • username • authToken (md5(username + md5(password))) • api_key • api_sig • Returns session key • Make API call with sk (session key) • Note: Try to keep credentials in one area to facilitate later changes

13. Last.fm auth.getmobilesession • auth.getmobilesession • Result with new session key http://ws.audioscrobbler.com/2.0/?method=auth.getmobilesession&api_key=be8c2…&username=chudsonfm&authToken=4eb71…&api_sig=e93fb… <lfm status="ok”> <session> <name>chudsonfm</name> <key>142c0085138a4b72d1782215b1da770a</key> <subscriber>0</subscriber> </session> </lfm> username (Required) : The last.fm username. authToken (Required) : A 32-byte ASCII hexadecimal MD5 hash of the user's Last.fm credentials. api_key (Required) : A Last.fm API key. api_sig (Required) : A Last.fm method signature.

14. Last.fm – Call Execution • Now we can make the call with our sk (session key) – user.getinfo • Response http://ws.audioscrobbler.com/2.0/?method=user.getinfo&api_key=be8c2…&sk=142c0…&api_sig=ccbd1…cc9dd • <lfm status="ok”> • <user> • <id>17317105</id> • <name>chudsonfm</name> • <realname/> • <url>http://www.last.fm/user/chudsonfm</url> • <image/> • <lang>en</lang> • <country/> • <age/> • <gender>n</gender> • <subscriber>0</subscriber> • <playcount>0</playcount> • <playlists>0</playlists> • </user> • </lfm> sk (Required) : The session key returned by auth.getMobileSession service. api_key (Required) : Your 32-character API key. api_sig (Required) : Your API method signature

15. Speed Traps • Could be on wifi, 3G or 1G based signal and bandwidth • Segment functionality / calls to prevent issues • Standard Apple test for approval is bandwidth usage when on cell network • Polling • Create subset of calls and functionality when on slower bandwidth • Use notifications if possible • Modify polling interval based on need • Recovery from intermittent or lost connections • Test the use of APIs via public vendor API test tools on various bandwidths

16. Large Data Set Handling • Decreasing returns for XML with large data sets and repetitive XML sections • Even more the case with mobile devices given: • Communication challenges • Memory and processing limitations • Minimize large data sets: • Use Just-in-Time (JIT) methodology • Ask for only those elements that you require • Ask for only those items that you require • Store what you can locally instead of requesting the same data

17. Response Processing • Leverage Stream Parsing for mobile environments • Provides low memory overhead • But, requires more heavy lifting • iPhone SDK based on stream parsing – NSXMLParser class • Android has Xstream as the streaming parser

18. iPhone Parsing • NSXMLParser delegate methods • 5 key methods • Parser:didStartElement: • Parser:foundCharacters: • Parser:didEndElement: • Parser:didEndDocument: • Parser:parseErrorOccurred:

19. Typical didStartElement, foundCharacters, and didEndElement

20. Parsing • In long parsing streams provide feedback when available • Example: Control4 My House • Home control from your iTouch/iPhone • During initial project load describes the sections being processed • Stores those items that will not change including house devices • But when providing current data, requests from server current state • Blends stored information with real time status information to provide display

21. Filtering • Types of Request Filtering • Selection criteria for narrowing data set returned • In general determine how efficient are the calls – reduce data waste • How much extra data, streaming, parsing is happening to access the data you use? How much data is being dropped on the floor? <?xml version="1.0" encoding="utf-8"?> <FindItemsAdvancedRequest xmlns="urn:ebay:apis:eBLBaseComponents"> <!-- Standard Input Fields --> <MessageID> string </MessageID> <!-- Call-specific Input Fields --> <BidCountMax> int </BidCountMax> <BidCountMin> int </BidCountMin> <CategoryHistogramMaxChildren> int </CategoryHistogramMaxChildren> <CategoryHistogramMaxParents> int </CategoryHistogramMaxParents> <CategoryID> string </CategoryID> <CharityID> int </CharityID> <Condition> ItemConditionCodeType </Condition> <Currency> CurrencyCodeType </Currency> … <ShippingLocation> CountryCodeType </ShippingLocation> <ShippingPostalCode> string </ShippingPostalCode> <SortOrder> SortOrderCodeType </SortOrder> <StoreName> string </StoreName> <StoreSearch> StoreSearchCodeType </StoreSearch> </FindItemsAdvancedRequest>

22. Paging • Provide paging functionality to users • Not all calls have paging available • Inform user of current location in set, easy access to next and previous if applicable • Cache key information depending on • The user flow (detail page from results page) • The aging of the information (when does it expire)

23. Page Requests Specify the page that you are requesting <PageNumber> • How many items are on a page • Set the number of entries per page returned <MaxEntries> • http://developer.ebay.com/products/overview/ <?xml version="1.0" encoding="utf-8"?> <FindItemsAdvancedRequestxmlns="urn:ebay:apis:eBLBaseComponents"> <PageNumber>2</PageNumber> <QueryKeywords>iphone</QueryKeywords> <MaxEntries>20</MaxEntries> </FindItemsAdvancedRequest>

24. List Paging Example • Must cache of course the current page • Remember though the total pages can change dynamically so check total pages after subsequent requests <TotalItems> int </TotalItems> <TotalPages> int </TotalPages> <?xml version="1.0" encoding="utf-8"?> <FindItemsAdvancedResponse xmlns="urn:ebay:apis:eBLBaseComponents"> <Timestamp>2007-07-06T00:51:05.250Z</Timestamp> <Ack>Success</Ack> <Build>e525_core_APILW_4863605_R1</Build> <SearchResult> <ItemArray> <Item> <ItemID>123000268897</ItemID> <EndTime>2009-07-23T09:26:21.000Z</EndTime> … </Item> <Item> <ItemID>123000268898</ItemID> <EndTime>2009-07-24T09:26:21.000Z</EndTime> … </Item> …. </ItemArray> </SearchResult> <PageNumber>2</PageNumber> <TotalPages>6</TotalPages> <TotalItems>103</TotalItems> … </FindItemsAdvancedResponse>

25. Display • Caching of information for future retrieval and navigation • Be careful of data aging depending on what is being shown • Execute web service parsing and display in background when possible to prevent UI blocking • example – eBay item description and images • When parsing large data blocks, progress indications can be provided from element name (sections of the XML) • Synchronous versus Asynchronous calls • Use JIT and Information on Demand to maximize small layouts and minimize web service calls

26. Caching Options • To minimize API round trips leverage caching and storage • Cache in memory • Cache in onboard light weight database or file • Off device persistence

27. Expanding Your Options

28. Blending Multiple Results • What if you have to: • Blend results from multiple calls in the same API • Blend results from multiple API sources • This could take the form of: • Extra item information on top of item details call • Note this is simplified so does not show authentication and authorization checking, encoding, or the like. Mobile View Mobile App API Service Trigger Request 1 Fulfill Result 1 Request 2 Fulfill Result 2 Blend Outlet

29. Blending Multiple Services • Multiple Services • Dependent on multiple services • Example: • Weather request from additional WS based on zip code returned by latitude and longitude from a geoposition service Mobile View Mobile App API Service 1 API Service 2 Trigger Request 1 Fulfill Result 1 Request 2 Fulfill Result 2 Blend Outlet

30. Proxy Server Solution • Provides layer of abstraction to consolidate or manage web services • Proxy Server retrieves data on demand or on scheduled basis • Allows for single consolidated call from the mobile device • Processes data and returns subset or stores data for retrieval later • Can also reduce API calls by caching similar results across user • Allows for extending business logic layer

31. Proxy Flow • Provides for single round trip for mobile application • Provides easy maintenance of web services business logic layer • Easily modify • Business logic • API credentials Mobile View Mobile App Proxy Server API Services Trigger Request Request Fulfill Result Request Fulfill Result Result Outlet

32. Proxy Landscape Web Service Web Service Proxy Server

33. Designing your WS/API Destiny

34. Creating Web Services • Try to serve lowest common device • Balance flexibility with overhead in calls: • Filtering of criteria and paging of data functionality • Split out high traffic calls versus critical requests • Easy but secure authentication and authorization for both the consumer and application • Benefit for mobile consumers, application programmers and web service providers • Decreased round trips • Increased efficiency of calls and applications • Better use of call volume restrictions • User experience improves

35. Wrap Up Provide user preference options that translate into better tuned API calls - number of items to show on a page as an example This will translate to data efficiency, fewer callers and greater use of data retrieved Minimize the number of trips, combine in single calls when possible Leverage caching and data storage when allowed Balance data granularity with length of returns for parsing Final thought to ponder The mobile device that is typically serving as a web service client could in the now or future be a web service provider…

36. Thank youSlides available at:www.aduci.com/web2expo2009sf.ppt Chuck Hudson chudson@aduci.com aduci

37. Appendix A - Resources • API / Web Service Online Catalogues • Programmable Web • www.programmableweb.com/api • Web Service List • www.webservicelist.com

38. Appendix B – Code Resources • iPhone URL Connections • http://developer.apple.com/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLConnection.html • iPhone Rest Wrapper • ihttp://github.com/akosma/iphonerestwrapper/tree/master • iPhone XML Parsing – Cocoa Stream Parser • http://developer.apple.com/documentation/Cocoa/Conceptual/XMLParsing/XMLParsing.html • SOAP with iPhone examples • http://icodeblog.com/2008/11/03/iphone-programming-tutorial-intro-to-soap-web-services/ • http://developer.omniture.com/node/321 • Façade Server landscape – O’REILLY – Windows platform • http://www.ondotnet.com/pub/a/dotnet/2004/02/23/mobilewebserviceapps.html • Connecting to Web Services – Sean Sullivan • http://www.slideshare.net/sullis/connecting-to-web-services-on-android

39. Appendix C - Efficient XML Interchange (EXI) • W3C Working Draft 19 September 2008 - http://www.w3.org/TR/2008/WD-exi-20080919/ • “EXI is a very compact representation for the Extensible Markup Language (XML) Information Set that is intended to simultaneously optimize performance and the utilization of computational resources.” • Components of XML Complexity 1. size 2. total number of elements 3. number of unique elements 4. tree-height (nesting) 5. number of unique external references 6. total number of attributes 7. number of unique attributes 8. regularity, or "self-similarity"

40. Appendix D - Other Auth Examples • Facebook • Notice the session key expiration • http://wiki.developers.facebook.com/index.php/Authorizing_Applications • Oauth • MPOAuthMobile – compiled in project library - Karl Adam • http://code.google.com/p/mpoauthconnection/wiki/MPOAuthMobile <?xml version="1.0" encoding="UTF-8"?> <auth_getSession_responsexmlns="http://api.facebook.com/1.0/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://api.facebook.com/1.0/ http://api.facebook.com/1.0/facebook.xsd"> <session_key>5f34e11bfb97c762e439e6a5-8055</session_key> <uid>8055</uid> <expires>1243814400</expires> </auth_getSession_response>