Building services with AtomPub

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
• MuleSource

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

• Dans Blog
• 2007-11-07T183002Z
• Dan Diephouse
• urnuuid60a76c80-d399-11d9-b91C-0003939e0af6
  
• Building services with AtomPub
• rvices"/
• urnuuid1225c695-cfb8-4ebb-aaaa-80da344efa
  6a
• 2007-11-07T183002Z
• (you must have content or a summary)

8
Atom Publishing Protocol Model
9
APP Model Services Workspaces

• xmlnsatom"http//www.w3.org/2005/Atom"
• Dans Website
• href"http//netzooid.com/blog/feed"
• Dans Blog
• href"http//netzooid.com/pics"
• Dans Pictures
• image/png
• image/jpeg
• image/gif

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
AtomPub Resources

• Description

12
GET /

• xmlnsatom"http//www.w3.org/2005/Atom"
• Dans Website
• href"http//netzooid.com/blog/feed"
• Dans Blog
• href"http//netzooid.com/pics"
• Dans Pictures
• image/png
• image/jpeg
• image/gif

13
GET /

• xmlnsatom"http//www.w3.org/2005/Atom"
• Dans Website
• href"http//netzooid.com/blog/feed"
• Dans Blog
• href"http//netzooid.com/pics"
• Dans Pictures
• image/png
• image/jpeg
• image/gif

14
GET /blog/feed

• Dans Blog
• 2007-12-13T183002Z
• Dan Diephouse
• urnuuid60a76c80-d399-11d9-b91C-0003939e0af6
  
• Building services with AtomPub
• es"/
• es
• rel"edit"/
• urnuuid1225c695-cfb8-4ebb-aaaa-80da344efa
  6a
• 2007-12-13T183002Z

15
A note on

• 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

• Building services with AtomPub
• s"/
• rvices.atom
• reledit /
• urnuuid1225c695-cfb8-4ebb-aaaa-80da344efa6
  a
• 2007-12-13T183002Z

17
POST /blog/feed (request)

• Atom Pub Patterns
• urnuuid1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxx
  x
• 2007-11-07T183002Z
• There are many ways to integrate with Atom
  services

18
POST /blog/feed (response)

• Location http//netzooid.com/blog/feed/patterns.a
  tom
• Atom Pub Patterns
• urnuuid1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxx
  x
• 2007-11-07T183002Z
• 
  
• ns.atom
• reledit /
• There are many ways to integrate with Atom
  services

19
GET /blog/feed/patterns.atom

• Atom Pub Patterns
• urnuuid1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxx
  x
• 2007-11-07T183002Z
• 
  
• ns.atom
• reledit /
• There are many ways to integrate with Atom
  services

20
PUT /blog/feed/patterns (request)

• Atom Pub Patterns
• urnuuid1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxx
  x
• 2007-11-08T183002Z
• AtomPub can be used in a variety of
  integration
• scenarios.

21
DELETE /blog/feed/patterns

• 200 OK

22
ETag Example
Client
Server

• HTTP/1.1 200 OK
• Date
• ETag "3e86-410-3596fbbc"
• Content-Length 1040
• Content-Type text/html

• GET /blog/feed
• Host netzooid.com

Server
Client
HTTP/1.1 304 Not Modified Date ETag
"3e86-410-3596fbbc" Content-Length 0

• GET /blog/feed
• If-None-Match
• "3e86-410-3596fbbc"
• Host netzooid.com

23
Media Resources and Media Link Entries

• What about data which you dont want to
  necessarily redistribute all the time?
• i.e. its 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
Media Resources

• Description

25
Service

• xmlnsatom"http//www.w3.org/2005/Atom"
• Dans Website
• href"http//netzooid.com/blog/feed"
• Dans Blog
• href"http//netzooid.com/pics"
• Dans Pictures
• image/png
• image/jpeg
• image/gif

26
POST /pics/ (request)

• Content-Type image/png
• Slug Dan Rambles
• binary data

27
POST /pics/ (request)

• Dan rambles
• urnuuid1225c695-cfb8-4ebb-aaaa-80da344efe6
  b
• 2007-11-07T172643Z
• Dan Diephouse
• src"http//netzooid.com/pics/dan_rambles.png"
  /
• href"http//netzooid.com/pics/dan_rambles.png"
  /
• href"hhttp//netzooid.com/pics/dan_rambles.ato
  m" /

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 youll 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 dont 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

• Contacts
• 2007-12-13T183002Z
• Contact Manager
• urnuuid60a76c80-d399-11d9-b91C-0003939e0af6
  
• Dan Diephouse
• phouse
• rel"edit"/
• urnuuid1225c695-cfb8-4ebb-aaaa-80da344efa
  6a
• 2007-12-13T183002Z
• Dan Diephouse
  1 555.555.5555

36
GET /contacts

• Contacts
• 2007-12-13T183002Z
• Contact Manager
• urnuuid60a76c80-d399-11d9-b91C-0003939e0af6
  
• Dan Diephouse
• phouse
• rel"edit"/
• urnuuid1225c695-cfb8-4ebb-aaaa-80da344efa
  6a
• 2007-12-13T183002Z
• Dan Diephouse
  1 555.555.5555

37
PUT /contacts/dan_diephouse

• Dan Dipehouse
• urnuuid1225c695-cfb8-4ebb-aaaa-80da344efa6
  a
• 2007-12-13T183002Z
• name"Dan Diephouse"
• phone"10000000000"
• city"Grand Rapids"

38
Microformat

• Contacts
• 2007-12-13T183002Z
• Contact Manager
• urnuuid60a76c80-d399-11d9-b91C-0003939e0af6
  
• Dan Diephouse
• phouse
• rel"edit"/
• urnuuid1225c695-cfb8-4ebb-aaaa-80da344efa
  6a
• 2007-12-13T183002Z
• Dan Diephouse
• 1 555 555 5555

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

• /opensearch/1.1/"
• Contact Search
• Search the contact
  database.
• example web
• admin_at_example.com
• type"application/atomxml"
• template"http//example.com/?qsearchTerms
  amppwstartPage?" /

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

• xmlnsopensearch"http//a9.com/-/spec/opensearc
  h/1.1/"
• rel"search"
• href"http//example.com/opensearchdescription
  .xml"
• type"application/opensearchdescriptionxml"
• title"Content Search" /

44
GET /feed?qDanpw0

• ...
• 35ults
• 1
  
• 10Page
• searchTerms"Dan" startPage"1" /
• type"text/html"/
• type"application/atomxml"/
• type"application/atomxml"/
• type"application/atomxml"/
• type"application/atomxml"/
• escriptionxml"
• href"http//example.com/opensearchdescrip
  tion.xml"/
• ...
• phone"15555555555"

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 Googles APIs

47
Batch

• APP doesnt 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

• ... what to insert ...
• ... what to update ...
• ... what to delete ...
• ... what to query ...

49
GData Batch response

• ...
• itemB

50
Thoughts on GData

• Weakness in APP?
• Or strength because its extensible?

51
Hierarchies

• How do I model collections of collections/trees/hi
  erarchies?
• Example

1 N
1 N
52
Hierarchical data with Atom

• Customer Acme Inc.
• urnuuid1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxx
  x
• 2007-11-07T183002Z
• Acme Inc.
• href"http//example.com/customers/purchaseOrd
  ers"
• Purchase Orders

53
Hierarchical data with Atom

• Customer Acme Inc.
• urnuuid1225c695-cfb8-4ebb-aaaa-xxxxxxxxxxx
  x
• 2007-11-07T183002Z
• Acme Inc.
• href"http//example.com/customers/purchaseOrd
  ers"
• rel"purchase-orders"
• Purchase Orders
• href"http//example.com/customers/contacts"
• rel"contacts"
• Contacts

54
Thoughts on Hierarchies

• It works!
• But is ugly Clients do not inherently understand
  hierarchies
• Multiple collections require rel attribute,
  which makes the relationships even less clear

55
Eventing

• Publish and consume entries which map to events
• Application level events
• Exceptions/fault monitoring
• Business level events
• A expense over 1000 was registered
• Use query parameters to narrow down the criteria
• Works with any client which understands Atom
• Powerful combination with opensearch

56
Security

• Goals?
• Privacy, Integrity, authentication, authorization
• SSL
• HTTP Auth
• WSSE
• Google Auth
• XML Signature Encryption

57
Why not?
58
Why not AtomPub?

• More appropriately when not
• Data is not time indexed
• Universality does not yield any benefits
• Batch
• Performance
• Messaging may be a more appropriate model
• Hierarchy kinda sucks
• Transactions

59
Contrasts and Comparisons

• A possibly pointless comparison to WS-

60
Comparing to WS- scaling

• AtomPub

• WS-

• Builds on HTTPs scalability
• Stateless
• ETags
• Caching

• No inherent caching/etags
• Can be stateless or stateful
• A message oriented approach which may be more
  suited to some applications
• (there is also Atom over XMPP)

61
Comparisons feature applicability

• AtomPub

• WS-

• Constraints in format bring universality, but
  also limit use cases
• Covers many of the security, reliability use
  cases
• Requires dev to know HTTP ins and outs

• Provides useful things like
• Message ordering
• WS-Trust
• WS-Policy
• Of course it also provides things like
• WSDL
• Interop problems
• Complexity

62
Comparisons interoperability

• AtomPub

• WS-

• Atom format is widely understood
• Avoids interop problems by not trying to support
  everything WS- supports
• Proprietary extensions are still liable to have
  interop problems just like WS-

• Core (SOAP/WSDL/Schema) is highly interoperable
  now
• WS- is interoperable to various degrees, mainly
  on Java/.NET

63
Comparisons developers

• AtomPub

• WS-

• Currently a pain to muck with many HTTP libraries
  and Atom parsers
• Improving with future releases of APP frameworks
• Simple and understandable

• Can write a .NET/Java interop application within
  a couple minutes
• Must understand WSDL, XML-Schema, SOAP, WS-I BP,
  etc, etc

64
The one true protocol?

• No, but
• AtomPub can be applied to a wide variety of
  business applications
• Universality can be powerful
• Hypertext model is powerful
• AtomPub is a great example of how to build a
  RESTful protocol

65
Questions?

• Blog http//netzooid.com/blog
• Email dan.d_at_mulesource.com
• Some stuff Ive been working on
• http//incubator.apache.org/abdera
• http//www.mulesource.org/display/ABDERA