1. Presented by group #3 Olena Hunsicker and Divya Josyula
The Atom Publishing Protocol (RFC 5023 October 2007) J. Gregorio, Google B. de hOra, NewBay Software
Presented by group #3 Olena Hunsicker and Divya Josyula

2. Index Introduction Terminology Brief Overview Collections
- Description
- Resource Classification
Protocol Documents
- Category Documents
- Service Documents
Creating Resources
Creating Media Resources and Media Link Entries
Editing Media Resources and Media Link Entries
Listing Collections
Caching and Entity Tags
Security Considerations
Blogger and APP example
Conclusion

3. Introduction
The Protocol was issued as a Proposed Standard in IETF RFC 5023 in October 2007
Atom Publishing protocol is based on the content management of resources using basic HTTP protocol operations like GET, PUT,POST and DELETE.
Atom Publishing Protocol uses REST principles for accessing resources

4. Introduction HTTP CRUD
Representational State Transfer : In order to manipulate resources, components of the internet (clients and servers) communicate via a standardized interface (e.g. HTTP) and exchange representations of these resources (the actual documents conveying the information)
HTTP
CRUD
POST
Create,Update Delete
GET
Read
PUT
Create,Update
DELETE
Delete

5. Terminology - A set or group of resources Collection Service document
- Gives a description of the available collections of resources
Category document
- Gives a description of the various categories in the collection

6. Brief Overview ATOM protocol provides facilities for :
Publishing - pushing content out to others, or simply granting digital access rights to certain content to a particular person or group of persons.
Retrieving Service Information
Retrieving Service Documents giving a Description of the available collections.
Retrieving collections
A set of resources can be retrieved in whole or in part as collections.
Retrieving Category Information
Retrieving Category Documents giving a description of the categories provided in the resource.
Managing resources - Creating, Editing or Deleting Resources like blog entries , wiki pages etc.

7. Collections-Description
A collection is a group of resources called member resources.
A collection is represented as an atom feed document where the feed’s entries contain the IRI’s and metadata about the collection’s member resources
<feed xmlns="
xml:base="
<id>
<title>My Blog Entries</title>
<updated> T13:40:03Z</updated>
<link rel="self" href="/blog/entries" />
<link href=" />
<entry>
<id>tag:example.org,2006:/blog/entries/1</id>
<title>Atom-Powered Robots Run Amok</title>
<link href="
<link rel="edit" href=" />
<author><name>James</name></author>
<summary>Some text.</summary>
</entry>
...
</feed>

8. Collections- Resource Classification
<feed xmlns="
xml:base="
<id>
<title>My Blog Entries</title>
<updated> T13:40:03Z</updated>
<link rel="self" href="/blog/entries" />
<link href=" />
<entry>
<id>tag:example.org,2006:/blog/entries/1</id>
<title>Atom-Powered Robots Run Amok</title>
<link href="
<link rel="edit" href=" />
<author><name>James</name></author>
<summary>Some text.</summary>
</entry>
<entry xmlns="
<id>tag:example.org,2006:/blog/photos/a_trip_to_the_beach</id>
<title>A trip to the beach</title>
<link rel="edit"
href=" />
<link rel="edit-media" type="image.png"
href=" />
<updated> T14:11:04Z</updated>
<summary>A trip to the beach</summary>
<content type="image/png"
src=" />
...
</feed>
MEMBER RESOURCES
ENTRY RESOURCES
MEDIA RESOURCES
MEDIA LINK ENTRY

9. Protocol Documents

10. Category Documents
Category Documents contain a list of categories specifying the categories supported by the resources
Example :
<?xml version="1.0" ?>
<app:categories
xmlns:app="
xmlns:atom="
fixed="yes" scheme="
<atom:category term="animal" />
<atom:category term="vegetable" />
<atom:category term="mineral" />
</app:categories>

11. IRI’s,categories,media types IRI’s,categories,media types
Service Documents
These documents contain a description of the available collections and their locations
The collections are grouped into workspaces
Service
Workspace
Collection
IRI’s,categories,media types
Workspace
Collection
IRI’s,categories,media types

12. Service Document – Example
Service
Main Site
My Blog Entries
Workspace
Pictures
Collections
SideBar Blog
Remaindered Links

13. Service Document – Example
<?xml version="1.0" encoding="utf8" ?>
<service xmlns=" xmlns:atom="
<workspace>
<atom:title>Main Site</atom:title>
<collection href="
<atom:title>My Blog Entries</atom:title>
<categories href=" />
</collection>
<collection href="
<atom:title>Pictures</atom:title>
<accept>image/png</accept>
<accept>image/jpeg</accept>
<accept>image/gif</accept>
</workspace>
<workspace>
<atom:title>Sidebar Blog</atom:title>
<collection
href=" >
<atom:title>Remaindered Links</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories fixed="yes">
<atom:category
scheme="
term="joke" />
term="serious" />
</categories>
</collection>
</workspace>
</service>

14. Service Document – Example
<?xml version="1.0" encoding="utf8" ?>
<service xmlns=" xmlns:atom="
<workspace>
<atom:title>Main Site</atom:title>
<collection href="
<atom:title>My Blog Entries</atom:title>
<categories href=" />
</collection>
<collection href="
<atom:title>Pictures</atom:title>
<accept>image/png</accept>
<accept>image/jpeg</accept>
<accept>image/gif</accept>
</workspace>
<workspace>
<atom:title>Sidebar Blog</atom:title>
<collection
href=" >
<atom:title>Remaindered Links</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories fixed="yes">
<atom:category
scheme="
term="joke" />
term="serious" />
</categories>
</collection>
</workspace>
</service>

15. Service Document – Example
<?xml version="1.0" encoding="utf8" ?>
<service xmlns=" xmlns:atom="
<workspace>
<atom:title>Main Site</atom:title>
<collection href="
<atom:title>My Blog Entries</atom:title>
<categories href=" />
</collection>
<collection href="
<atom:title>Pictures</atom:title>
<accept>image/png</accept>
<accept>image/jpeg</accept>
<accept>image/gif</accept>
</workspace>
<workspace>
<atom:title>Sidebar Blog</atom:title>
<collection
href=" >
<atom:title>Remaindered Links</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories fixed="yes">
<atom:category
scheme="
term="joke" />
term="serious" />
</categories>
</collection>
</workspace>
</service>

16. Service Document – Example
<?xml version="1.0" encoding="utf8" ?>
<service xmlns=" xmlns:atom="
<workspace>
<atom:title>Main Site</atom:title>
<collection href="
<atom:title>My Blog Entries</atom:title>
<categories href=" />
</collection>
<collection href="
<atom:title>Pictures</atom:title>
<accept>image/png</accept>
<accept>image/jpeg</accept>
<accept>image/gif</accept>
</workspace>
<workspace>
<atom:title>Sidebar Blog</atom:title>
<collection
href=" >
<atom:title>Remaindered Links</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories fixed="yes">
<atom:category
scheme="
term="joke" />
term="serious" />
</categories>
</collection>
</workspace>
</service>

17. Our approach to studying APP
We are not going to take this approach
Will take a look at:
- HTTP requests and responses headers
- Atom Entries

18. Creating Resources with POST
201 “Created”
POST request

19. Creating Resources with POST
POST /edit/ HTTP/1.1
Host: example.org
User-Agent: Thingio/1.0
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Type: application/atom+xml;type=entry
Content-Length: nnn
Slug: First Post
<?xml version="1.0"?>
<entry xmlns="
<title>Atom-Powered Robots Run Amok</title>
<id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
<updated> T18:30:02Z</updated>
<author><name>John Doe</name></author>
<content>Some text.</content>
</entry>
Request to use header’s value as a part of URIs (can be ignored or altered)

20. Creating Resources with POST
HTTP/ Created
Date: Fri, 7 Oct :17:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry;charset="utf-8“
Location:
ETag: "c180de84f991g8"
<?xml version="1.0"?>
<entry xmlns="
<title>Atom-Powered Robots Run Amok</title>
<id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
<updated> T18:30:02Z</updated>
<author><name>John Doe</name></author>
<content>Some text.</content>
<link rel="edit" href="
</entry>
URI of Atom Entry, content of Slug header was used
Created Entry may not
match the entry POSTed

21. Adding Media Resources to a Collection
APP allows to add arbitrary media resources such as photographs, documents, audio/video recordings ect. to the collection.
The server creates an Atom Entry document - Media Link Entry - which linked to the Media Resource posted by the client.

22. Adding Media Resources to a Collection
Location:
<content type="image/png" src="
201 “Created”
POST request

23. Adding Media Resources to a Collection
POST /edit/ HTTP/1.1
Host: media.example.org
Content-Type: image/png
Slug: The Sky
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Length: nnn
...some binary data...

24. Adding Media Resources to a Collection
HTTP/ Created
Date: Fri, 7 Oct :17:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry;charset="utf-8"
Location:
<?xml version="1.0"?>
<entry xmlns="
<title>The Sky</title>
<id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
<updated> T17:17:08Z</updated>
<author><name>Daffy</name></author>
<summary type="text" />
<content type="image/png" src="
<link rel="edit-media" href=" />
<link rel="edit" href=" />
</entry>
“MUST include the URI of the Media Link Entry” [1]
“MUST include atom:content element with src attribute”[1]
SHOULD include atom:link element with link relation “edit-media” – used to modify Media Resource
Used to retrieve, update, delete the Resource

25. Editing Media Resources with PUT
PUT /edit/the_sky.png HTTP/1.1
Host: media.example.org
Content-Type: image/png
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Length: nnn
...some binary data...
HTTP/ Ok
Date: Fri, 8 Oct :17:11 GMT
From Media Link Entry
“edit-media” link

26. Editing Media Link Entry with PUT
PUT /media/edit/the_sky.atom HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Type: application/atom+xml;type=entry
Content-Length: nnn
If-Match: "c181bb840673b5"
<?xml version="1.0"?>
<entry xmlns="
<title>The Beach</title>
<id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
<updated> T17:17:08Z</updated> <author><name>Daffy</name></author>
<summary type="text"> A nice sunset picture over the water. </summary>
<content type="image/png" src="
<link rel="edit-media" href=" />
<link rel="edit" href=" />
</entry>
HTTP/ Ok
Date: Fri, 7 Oct :19:11 GMT
Content-Length: 0

27. Deleting Resources DELETE /media/edit/the_sky.atom HTTP/1.1
Host: example.org
Authorization: BASIC ZGFmZnk6c2VjZXJldA==
HTTP/ OK
Date: Fri, 8 Oct :17:11 GMT

28. Listing Collections
Collection Resources represented in a form of Atom Feed Documents.
Collections can be large. On GET request MAY return partial lists.
First list MUST contain most recent resources and include atom:link element with next relation:
<link rel="next" href=" />

29. Collection Partial Lists
<feed xmlns="
<link rel="first" href=" />
<link rel="previous" href=" />
<link rel="next" href=" />
<link rel="last" href=" />
...
</feed>
Final Feed Document
10 linked Feed Documents

30. Caching and Entity Tags
Atom Publishing protocol based on HTTP transfer. Implementers advised to use cache controls when editing Resources
ETag : HTTP response header, opaque cache validator (RFC 2616)
Etag allows to determine if the client have the latest representation of Entry before editing

31. Caching and Entity Tags
To edit an entry, clients first need to retrieve an editable representation with GET request.
Use returned ETag to construct “conditional GET” request
Combined with If-None-Match HTTP headers

32. Caching and Entity Tags
Client: POST request
Server:
HTTP/ Created
Date: Fri, 23 Feb :17:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry
Location:
Content-Location:
ETag: "e180ee84f0671b1"
<?xml version="1.0" ?>
<entry xmlns="
<title>Atom-Powered Robots Run Amok</title>
<id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
<updated> T17:09:02Z</updated>
<author><name>Captain Lansing</name></author>
<content>It's something moving... solid metal</content>
</entry>

33. Caching and Entity Tags
***Atom Entry on the Server wasn’t modified
HTTP/ Not Modified
Date: Sat, 24 Feb :17:11 GMT
GET /edit/first-post.atom HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
If-None-Match: "e180ee84f0671b1"

34. Caching and Entity Tags
***Atom Entry on the Server has been modified
HTTP/ OK +
GET /edit/first-post.atom HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
If-None-Match: "e180ee84f0671b1"

35. Caching and Entity Tags
***Server has more recent copy than client
HTTP/ Precondition Failed
Date: Sat, 24 Feb :34:11 GMT
PUT /edit/first-post.atom HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Type: application/atom+xml;type=entry
Content-Length: nnn
If-Match: "e180ee84f0671b1"

36. Security Considerations
Atom Publishing Protocol does not require that implementations use authentication
At least Basic Authentication is recommended in order to prevent malicious clients from creating and modifying collection members.
On unauthorized request the web server sends HTTP response:
HTTP/ Unauthorized
Date: nnn
WWW-Authenticate: Basic realm=“my blog”

37. Security Considerations
Denial of Service Attacks (consume CPU, memory, disc space)
Replay attacks: APP cannot detect duplicate requests
Code injections: Entry Documents can contain executable content types; thus need to verify the client supplied content before processing and publishing

46. Retrieving “CS791 APP” blog homepage over telnet connection

47. Example of using Entity Tags

48. References:
1. “The Atom Publishing Protocol” RFC 5023, Oct. 2007,
2. “Blogger: Atom API documentation”