REST Services Caching

1. REST Services: HTTP caching

2. “A distributed system is one in which the failure
of a computer you didn’t even know existed can
render your own computer unusable.”
- Leslie Lamport

3. • REST stands for REpresentational State Transfer
• Representation is just a very simple rendering
of the object
• Has benefits when leverages existing HTTP
protocol
What is REST?

4. • Up-to-date
• Fresh
• Stale
States of Resource Representation

5. Up-to-Date state means the Representation is
current according to the origin server
Representation is being sent back with no expiry
and no caching instructions means the client is
allowed to cache for however long or not cache
at all
Up-to-Date State

6. Fresh State considered as long as the
Representation hasn’t expired at client side,
proxy or browser
Fresh State

7. • Sending must-revalidate means the client must
revalidate once the representation is Stale
• Stale means it’s gone over it’s expiration date
Stale State

8. • Doesn’t actually mean do not cache
• Means the client must revalidate both Fresh
and Stale entries and then may use the cached
copy if it’s up to date
No-cache Directive

9. • In plain English text format
• Starting line: Method URI
HTTP/version
• Headers
• Body
HTTP Message

10. Request:
GET /wiki HTTP/1.1
Host: wikipedia.org
Accept: text/html
Connection: close
Response:
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Language: en
Content-Length: 1234
Sample HTTP Request/Response

11. • Get
• Post
• Put
• Delete
• Options
• Head
• Patch
• Trace
• Link
• Unlink
• Connect
Cache-enabled methods are in Red
HTTP Methods

12. Response:
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 1234
Expires: Fri, 27 Jan 2012 02:33:12 GMT
•Allows only HTTP date
•Good for static resources
•Limited control
HTTP Expires header

13. • Enough for static content
• For things that rarely change
• Or don’t change at all like Calculator
/Calculator/Multiply?x=2&y=2/Calculator/Multiply?x=2&y=2 ClientClient
Expires is Enough?

14. • public
• private
• no-cache
• no-store
• max-age=[seconds]
• s-maxage=[seconds]
• must-revalidate
• proxy-revalidate
• no-transform
HTTP Cache-Control directives

15. Response:
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 1234
Cache-Control: max-age=3600, must-revalidate
HTTP Cache-Control Sample

16. What if we need to update data?
Cache-Control is Enough for REST

17. • Optimistic is when we version our data
• And do not have any transactions
• Make use of ETag, If-Match and If-None-
Match headers
Optimistic Locking: ETag

18. /Orders/Orders ClientClient
GET /Orders HTTP/1.1
HTTP/1.1 200 OK
Etag: 1
[content goes in body]
GET /Orders HTTP/1.1
If-None-Match: 1
HTTP/1.1 304 Not Modified
[no ETag]
[no content returned!]
ETag: GET Not Modified Resource

19. /Orders/Orders ClientClient
GET /Orders HTTP/1.1
HTTP/1.1 200 OK
Etag: 1
[content goes in body]
GET /Orders HTTP/1.1
If-None-Match: 1
HTTP/1.1 200 OK
Etag: 2
[new content goes in body!]
ETag: GET modified resource

20. /Orders/Orders ClientClient
HTTP/1.1 200 OK
Etag: 1
[content goes in body]
PUT /Orders HTTP/1.1
If-Match: 1
[new content goes in body]
HTTP/1.1 100 Continue
[no ETag]
[no content!]
GET /Orders HTTP/1.1
ETag: Modify Resource (PUT)

21. /Orders/Orders ClientClient
HTTP/1.1 200 OK
Etag: 1
[content goes in body]
PUT /Orders HTTP/1.1
If-Match: 1
[new content goes in body]
HTTP/1.1 412 Precondition Failed
[no ETag]
[no content!]
GET /Orders HTTP/1.1
ETag: Modify Changed Resource (PUT)

22. God damned HTTP!
What we gonna do?
• Override changes!
• Yeah! It’s possible!
• Download the latest version using GET method
• We will know the new Etag then
Etag: mismatch when PUT

23. /Orders/Orders ClientClient
HTTP/1.1 412 Precondition Failed
[no ETag]
[no content!]
PUT /Orders HTTP/1.1
If-None-Match: 1
[new content goes in body]
HTTP/1.1 100 Continue
[no ETag]
[no content!]
PUT /Orders HTTP/1.1
If-Match: 1
[new content goes in body]
Etag: Override Changes When PUT

24. • ETag and If-* headers came with HTTP 1.1
• In HTTP 1.0 there are another set of headers:
Last-Modified: Sat, 29 Oct 2011 19:43:31 GMT
If-Modified-Since: Sat, 29 Oct 2011 19:43:31
GMT
Additional HTTP Headers

25. int Multiply(int x, int y)int Multiply(int x, int y)
HTTPHTTP
IPC (Named Pipes)IPC (Named Pipes)
TCPTCP
ClientClient
TCPTCP
SOAPSOAP
UDPUDP
Web Services: Protocols

26. POST /search HTTP/1.1
Host: www.domain.com
Content-Type: application/x-www-form-
urlencoded
term=something
HTTP/1.1 303 See Other
Location: /search/something/1
POST-Redirect-GET pattern