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Building services with AtomPub

Building services with AtomPub. An exploration of Atom, AtomPub , REST, and HTTP. About me. Open Source: Mule, CXF/XFire, Abdera, Apache-* Exploring how to make building distributed services more powerful/approachable/scalable/etc <plug> MuleSource </plug>. Topic Map.

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Building services with AtomPub

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  1. Building services with AtomPub An exploration of Atom, AtomPub, REST, and HTTP

  2. About me • Open Source: Mule, CXF/XFire, Abdera, Apache-* • Exploring how to make building distributed services more powerful/approachable/scalable/etc • <plug>MuleSource</plug>

  3. Topic Map

  4. The model and the protocol

  5. Atom Roots • Atom was created out of frustration with the RSS format • Many inconsistencies, many different versions • Syndication format • Blogs • Monitoring • Search • Directories • Etc • IETF RFC 4287

  6. Atom Feed Structure (roughly) • Feed • ID • Author • Link • Title • Updated • * • Entry • ID • Updated • Link • Summary • Content • *

  7. The Bare Minimum Atom Feed <?xml version="1.0" encoding="utf-8"?> <feed xmlns="http://www.w3.org/2005/Atom"> <title>Dan’s Blog</title> <link href="http://netzooid.com/blog/"/> <updated>2007-11-07T18:30:02Z</updated> <author> <name>Dan Diephouse</name> </author> <id>urn:uuid:60a76c80-d399-11d9-b91C-0003939e0af6</id> <entry> <title>Building services with AtomPub</title> <link href="http://netzooid.com/blog/atompub_services"/> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id> <updated>2007-11-07T18:30:02Z</updated> <content> … (you must have content or a summary) </content> </entry> </feed>

  8. Atom Publishing Protocol Model

  9. APP Model: Services & Workspaces <service xmlns="http://www.w3.org/2007/app" xmlns:atom="http://www.w3.org/2005/Atom"> <workspace> <atom:title>Dan’s Website</atom:title> <collection href="http://netzooid.com/blog/feed"> <atom:title>Dan’s Blog</atom:title> </collection> <collection href="http://netzooid.com/pics"> <atom:title>Dan’s Pictures</atom:title> <accept>image/png</accept> <accept>image/jpeg</accept> <accept>image/gif</accept> </collection> </workspace> </service>

  10. What is the Atom Publishing Protocol? • Create, edit, delete resources • Extensible Protocol • Authentication extensions (i.e. WSSE) • Opensearch • GData • Properly uses HTTP so it can be scalable and reliable • Builds on Atom model

  11. Description AtomPub Resources

  12. GET / <service xmlns="http://www.w3.org/2007/app" xmlns:atom="http://www.w3.org/2005/Atom"> <workspace> <atom:title>Dan’s Website</atom:title> <collection href="http://netzooid.com/blog/feed"> <atom:title>Dan’s Blog</atom:title> </collection> <collection href="http://netzooid.com/pics"> <atom:title>Dan’s Pictures</atom:title> <accept>image/png</accept> <accept>image/jpeg</accept> <accept>image/gif</accept> </collection> </workspace> </service>

  13. GET / <service xmlns="http://www.w3.org/2007/app" xmlns:atom="http://www.w3.org/2005/Atom"> <workspace> <atom:title>Dan’s Website</atom:title> <collection href="http://netzooid.com/blog/feed"> <atom:title>Dan’s Blog</atom:title> </collection> <collection href="http://netzooid.com/pics"> <atom:title>Dan’s Pictures</atom:title> <accept>image/png</accept> <accept>image/jpeg</accept> <accept>image/gif</accept> </collection> </workspace> </service>

  14. GET /blog/feed <?xml version="1.0" encoding="utf-8"?> <feed xmlns="http://www.w3.org/2005/Atom"> <title>Dan’s Blog</title> <link href="http://netzooid.com/blog/"/> <updated>2007-12-13T18:30:02Z</updated> <author> <name>Dan Diephouse</name> </author> <id>urn:uuid:60a76c80-d399-11d9-b91C-0003939e0af6</id> <entry> <title>Building services with AtomPub</title> <link href="http://netzooid.com/blog/app_services"/> <link href="http://netzooid.com/blog/app_services“ rel="edit"/> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id> <updated>2007-12-13T18:30:02Z</updated> <content> … (you must have content or a summary) </content> </entry> </feed>

  15. A note on <link> • Entries contain a set of links • Each link has a relationship attribute • No “rel” attribute means its an alternate representation – i.e. HTML

  16. GET /blog/feed/app_services.atom <entry> <title>Building services with AtomPub</title> <link href="http://netzooid.com/blog/app_services"/> <link href="http://netzooid.com/blog/feed/app_services.atom“ rel=“edit” /> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id> <updated>2007-12-13T18:30:02Z</updated> <content> … </content> </entry>

  17. POST /blog/feed (request) <entry> <title>Atom Pub Patterns</title> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxxx</id> <updated>2007-11-07T18:30:02Z</updated> <content> There are many ways to integrate with Atom services… </content> </entry>

  18. POST /blog/feed (response) Location: http://netzooid.com/blog/feed/patterns.atom <entry> <title>Atom Pub Patterns</title> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxxx</id> <updated>2007-11-07T18:30:02Z</updated> <link href="http://netzooid.com/blog/patterns"/> <link href="http://netzooid.com/blog/feed/patterns.atom“ rel=“edit” /> <content> There are many ways to integrate with Atom services… </content> </entry>

  19. GET /blog/feed/patterns.atom <entry> <title>Atom Pub Patterns</title> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxxx</id> <updated>2007-11-07T18:30:02Z</updated> <link href="http://netzooid.com/blog/patterns"/> <link href="http://netzooid.com/blog/feed/patterns.atom“ rel=“edit” /> <content> There are many ways to integrate with Atom services… </content> </entry>

  20. PUT /blog/feed/patterns (request) <entry> <title>Atom Pub Patterns</title> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxxx</id> <updated>2007-11-08T18:30:02Z</updated> <content> AtomPub can be used in a variety of integration scenarios. … </content> </entry>

  21. DELETE /blog/feed/patterns 200 OK

  22. ETag Example HTTP/1.1 200 OK Date: … ETag: "3e86-410-3596fbbc" Content-Length: 1040 Content-Type: text/html … Client Server GET /blog/feed Host: netzooid.com … Client GET /blog/feed If-None-Match: "3e86-410-3596fbbc" Host: netzooid.com … Server HTTP/1.1 304 Not Modified Date: … ETag: "3e86-410-3596fbbc" Content-Length: 0…

  23. Media Resources and Media Link Entries • What about data which you don’t want to necessarily redistribute all the time? • i.e. it’s too large • What about non-XML data? • Images • APP defines: • Media Resource: your data • Media Link Entry: An atom entry which describes your data

  24. Description Media Resources

  25. Service <service xmlns="http://www.w3.org/2007/app" xmlns:atom="http://www.w3.org/2005/Atom"> <workspace> <atom:title>Dan’s Website</atom:title> <collection href="http://netzooid.com/blog/feed"> <atom:title>Dan’s Blog</atom:title> </collection> <collection href="http://netzooid.com/pics"> <atom:title>Dan’s Pictures</atom:title> <accept>image/png</accept> <accept>image/jpeg</accept> <accept>image/gif</accept> </collection> </workspace> </service>

  26. POST /pics/ (request) Content-Type: image/png Slug: Dan Rambles … binary data …

  27. POST /pics/ (request) <entry xmlns="http://www.w3.org/2005/Atom"> <title>Dan rambles</title> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efe6b</id> <updated>2007-11-07T17:26:43Z</updated> <author> <name>Dan Diephouse</name> </author> <summary type="text" /> <content type="image/png" src="http://netzooid.com/pics/dan_rambles.png" /> <link rel="edit-media" href="http://netzooid.com/pics/dan_rambles.png" /> <link rel="edit" href="hhttp://netzooid.com/pics/dan_rambles.atom" /> </entry>

  28. The Media Link Entry • You can add summary later or have it auto-generated from the content. • Allows you to store, browse, updated, delete anything! • Pictures • XML documents • Jars • Videos • Messages…

  29. Why oh why?

  30. Universal • Atom is widely understood • Provides ubiquitous elements which have meaning across all contexts • Summary/Content • Updated date • ID • Links • Clients do not need to understand your specific application to interact with it

  31. Leverage HTTP • AtomPub (nearly) guarantees you’ll follow RESTful best practices and have a scalable service • Uniform Interface • ETags • Caching • Reliability • Avoid writing your own protocol

  32. Existing Infrastructure • Many Atom/AtomPub libraries/frameworks are popping up • Abdera (Java) • Propono (Java) • Amplee (Python) • You don’t need a framework though: Just use HTTP • wget • commons httpclient • etc

  33. Building Services: Patterns and Strategies Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say that there is more stupidity than hydrogen, and that is the basic building block of the universe. – Frank Zappa

  34. Microcontent • Embed your own extensions inside Atom entries • Extensions become your model • Examples: • Contacts • Calendars • Event Monitoring • Purchase Orders • Anything…

  35. GET /contacts <feed xmlns="http://www.w3.org/2005/Atom"> <title>Contacts</title> <link href="http://example.org/contacts/"/> <updated>2007-12-13T18:30:02Z</updated> <author> <name>Contact Manager</name> </author> <id>urn:uuid:60a76c80-d399-11d9-b91C-0003939e0af6</id> <entry> <title>Dan Diephouse</title> <link href="http://example.org/contacts/dan_diephouse“ rel="edit"/> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id> <updated>2007-12-13T18:30:02Z</updated> <summary type="xhtml"> Dan Diephouse<br/> +1 555.555.5555 </summary> <acme:contact name="Dan Diephouse" phone="+15555555555" city="Grand Rapids"> </entry> </feed>

  36. GET /contacts <feed xmlns="http://www.w3.org/2005/Atom"> <title>Contacts</title> <link href="http://example.org/contacts/"/> <updated>2007-12-13T18:30:02Z</updated> <author> <name>Contact Manager</name> </author> <id>urn:uuid:60a76c80-d399-11d9-b91C-0003939e0af6</id> <entry> <title>Dan Diephouse</title> <link href="http://example.org/contacts/dan_diephouse“ rel="edit"/> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id> <updated>2007-12-13T18:30:02Z</updated> <summary type="xhtml"> Dan Diephouse<br/> +1 555.555.5555 </summary> <acme:contact name="Dan Diephouse" phone="+15555555555" city="Grand Rapids"> </entry> </feed>

  37. PUT /contacts/dan_diephouse <entry> <title>Dan Dipehouse</title> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id> <updated>2007-12-13T18:30:02Z</updated> <summary/> <acme:contact name="Dan Diephouse" phone="+10000000000" city="Grand Rapids"> </entry>

  38. Microformat <feed xmlns="http://www.w3.org/2005/Atom"> <title>Contacts</title> <link href="http://example.org/contacts/"/> <updated>2007-12-13T18:30:02Z</updated> <author> <name>Contact Manager</name> </author> <id>urn:uuid:60a76c80-d399-11d9-b91C-0003939e0af6</id> <entry> <title>Dan Diephouse</title> <link href="http://example.org/contacts/dan_diephouse“ rel="edit"/> <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id> <updated>2007-12-13T18:30:02Z</updated> <content type="xhtml"> <span class="name">Dan Diephouse</span> <span class="phone">+1 555 555 5555</span> <span class="city">Grand Rapids</span> </content> </feed>

  39. Microcontent • Microcontent can be anything to do with your application • Summary, date, link, id can provide information which is understandable by everyone • Atom servers preserve all metadata not specifically updated • Media entries may be more suitable for some applications – even if you are using XML content • Becomes searchable with things like OpenSearch & GData…

  40. OpenSearch • An XML format for describing how to query resources • Like WSDL for search…

  41. Example <OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/"> <ShortName>Contact Search</ShortName> <Description>Search the contact database.</Description> <Tags>example web</Tags> <Contact>admin@example.com</Contact> <Url type="application/atom+xml" template="http://example.com/?q={searchTerms}&amp;pw={startPage?}" /> </OpenSearchDescription>

  42. OpenSearch • Offers a way to tell people how to search your service • Several standard parameters: • searchTerms: Search criteria • count: The number of results per page • startPage: The page of results • language: The language of the results • etc.. • Define your own terms as well

  43. Example <?xml version="1.0" encoding="UTF-8"?> <feed xmlns="http://www.w3.org/2005/Atom" xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/"> <!-- ... ---> <link rel="search" href="http://example.com/opensearchdescription.xml" type="application/opensearchdescription+xml" title="Content Search" /> <!-- ... ---> </feed>

  44. GET /feed?q=Dan&pw=0 <feed xmlns="http://www.w3.org/2005/Atom"> ... <opensearch:totalResults>35</opensearch:totalResults> <opensearch:startIndex>1</opensearch:startIndex> <opensearch:itemsPerPage>10</opensearch:itemsPerPage> <opensearch:Queryrole="request" searchTerms="Dan" startPage="1" /> <link rel="alternate" href="...search.html?pw=1" type="text/html"/> <link rel="self" href="...?q=Dan&amp;pw=1" type="application/atom+xml"/> <link rel="first" href="...?q=Dan&amp;pw=1" type="application/atom+xml"/> <link rel="next" href="...?q=Dan&amp;pw=2" type="application/atom+xml"/> <link rel="last" href="...?q=Dan&amp;pw=4" type="application/atom+xml"/> <link rel="search" type="application/opensearchdescription+xml" href="http://example.com/opensearchdescription.xml"/> <entry> ... <acme:contactname="Dan Diephouse" phone="+15555555555" city="Grand Rapids"> </entry> </feed>

  45. What is GData? “simple standard protocol for reading and writing data on the web”

  46. What does that mean? • Standard way to query feeds • Specifies optimistic concurrency model • Way to authenticate users • Common elements for Google services • A way to do batch operations • All built on AtomPub • Used for all Google’s APIs

  47. Batch • APP doesn’t specify a way to do batch operations • GData supplies one way, but it has received a cold reception as a general purpose way to do batch things • Some things to think about: • How do you deal with errors? • Does your batch method lose the benefits of the uniform interface?

  48. GData Batch <feed> <entry> <batch:operationtype="insert"/> ... what to insert ... </entry> <entry> <batch:operationtype="update"/> ... what to update ... </entry> <entry> <batch:operationtype="delete"/> ... what to delete ... </entry> <entry> <batch:operationtype="query"/> ... what to query ... </entry> </feed>

  49. GData Batch response <feed> <entry> ... <batch:operation type="insert"/> <batch:id>itemB</batch:id> <batch:status code="201" reason="Created"/> </entry> </feed>

  50. Thoughts on GData • Weakness in APP? • Or strength because its extensible?

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