Three Inconvenient Thruths about REST

1. TRE UBELEILIGE SANNHETER OM REST
COMPUTASDAG, 13. JUNI 2014
1

2. 2
Fra: http://martinfowler.com/articles/richardsonMaturityModel.html

3. SANNHET #1:
GET-kall er aldri nullipotent
3

4. 4
Fra: http://martinfowler.com/articles/richardsonMaturityModel.html

5. Hva betyr «nullipotent»?
5
Fra Wikipedia:
«The GET method is a safe method (or
nullipotent), meaning that calling it
produces no side-effects.»

6. 6
Tomcat Access
Log

7. Moteksempler
●
Access log som REST-ressurs
●
Tilgangskontroll
– Three strikes-regel
●
Engangsnedlasting
7

8. SANNHET #2:
HTTP Response Codes ≠ «REST Response Codes»
8

9. 9
Fra: http://martinfowler.com/articles/richardsonMaturityModel.html

10. 10
Fra: http://www.restapitutorial.com/httpstatuscodes.html

11. 11
Fra: http://www.restapitutorial.com/httpstatuscodes.html

12. 12
Fra: http://www.restapitutorial.com/httpstatuscodes.html

13. 13
Fra: http://www.restapitutorial.com/httpstatuscodes.html

14. Martin Fowler om HATEOAS
14
«The key elements that are supported
by the existence of the web are the
strong separation between safe (eg
GET) and non-safe operations, together
with using status codes to help
communicate the kinds of errors you
run into.»
http://martinfowler.com/articles/richardsonMaturityModel.html

15. SANNHET #3:
HATEOAS YAGNI⇒
15

16. 16
Fra: http://martinfowler.com/articles/richardsonMaturityModel.html

17. HATEOAS
17
Hypermedia as the engine of application
state
Fra Wikipedia:
«Clients make state transitions only
through actions that are dynamically
identified within hypermedia by the server.
Except for simple fixed entry points to the
application, a client does not assume that
any particular action is available for any
particular resources beyond those
described in representations previously
received from the server.»

18. Eksempel: Hire i EPIM LogisticsHub
18
<Hire id="h101442">
<CcuId>141705</CcuId>
<EnclosingHireIds>
<EnclosingHireId distance="1">a1</EnclosingHireId>
</EnclosingHireIds>
<OrgNo>123456789</OrgNo>
<GlnLocation>1234567890123</GlnLocation>
<StartDate>2013-10-09</StartDate>
<EndDate>2013-11-08</EndDate>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="get" rel="self"/>
<Link href="/ccus/141705" method="get" rel="Ccu"/>
<Link href="/ccus/141705/hires/a1" method="get" rel="EnclosingHire"/>
</Hire>

19. Eksempel: Hire i EPIM LogisticsHub
19
<Hire id="h101442">
<CcuId>141705</CcuId>
<EnclosingHireIds>
<EnclosingHireId distance="1">a1</EnclosingHireId>
</EnclosingHireIds>
<OrgNo>123456789</OrgNo>
<GlnLocation>1234567890123</GlnLocation>
<StartDate>2013-10-09</StartDate>
<EndDate>2013-11-08</EndDate>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="get" rel="self"/>
<Link href="/ccus/141705" method="get" rel="Ccu"/>
<Link href="/ccus/141705/hires/a1" method="get" rel="EnclosingHire"/>
</Hire>

20. Eksempel: Hire i EPIM LogisticsHub
20
<Hire id="h101442">
<CcuId>141705</CcuId>
<EnclosingHireIds>
<EnclosingHireId distance="1">a1</EnclosingHireId>
</EnclosingHireIds>
<OrgNo>123456789</OrgNo>
<GlnLocation>1234567890123</GlnLocation>
<StartDate>2013-10-09</StartDate>
<EndDate>2013-11-08</EndDate>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="get" rel="self"/>
<Link href="/ccus/141705" method="get" rel="Ccu"/>
<Link href="/ccus/141705/hires/a1" method="get" rel="EnclosingHire"/>
</Hire>
199 av totalt 477 tegn
(42%)

21. Eksempel: Hire i EPIM LogisticsHub, full HATEOAS
21
<Hire id="h101442">
<CcuId>141705</CcuId>
<EnclosingHireIds>
<EnclosingHireId distance="1">a1</EnclosingHireId>
</EnclosingHireIds>
<OrgNo>123456789</OrgNo>
<GlnLocation>1234567890123</GlnLocation>
<StartDate>2013-10-09</StartDate>
<EndDate>2013-11-08</EndDate>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="get" rel="self"/>
<Link href="/ccus/141705" method="get" rel="Ccu"/>
<Link href="/ccus/141705/hires/a1" method="get" rel="EnclosingHire"/>
<Link href="/organizations/123456789" method="get" rel="Organization"/>
<Link href="/organizations/123456789/locations/1234567890123" method="get" rel="Location"/>
<Link href="/ccus/141705/hires/a1/hires/h101442/documents" method="post" rel="Documents"/>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="put" rel="update"/>
<Link href="/ccus/141705/hires/a1/hires/h101442/hires" method="post" rel="addHire"/>
</Hire>
620 av totalt 899 tegn
(69%)

22. Martin Fowler om HATEOAS
22
«One obvious benefit of hypermedia
controls is that it allows the server to
change its URI scheme without
breaking clients. As long as clients look
up the “addTest” link URI then the
server team can juggle all URIs other
than the initial entry points.»
http://martinfowler.com/articles/richardsonMaturityModel.html

23. Martin Fowler om HATEOAS
23
«A further benefit is that it helps client
developers explore the protocol. The
links give client developers a hint as to
what may be possible next. It doesn't
give all the information: both the
“latest” and “cancel” controls point to
the same URI – they need to figure out
that one is a GET and the other a
DELETE. But at least it gives them a
starting point as to what to think about
for more information and to look for a
similar URI in the protocol
documentation.»
http://martinfowler.com/articles/richardsonMaturityModel.html

24. Kost/nytte av HATEOAS
Hva endrer seg oftest?
●
Oppførsel
●
Innhold
●
URLer
Hva er vanskelig å refaktorere?
●
Oppførsel
●
Innhold
●
URLer
24

25. Eksempel: Hire i EPIM LogisticsHub
25
<Hire id="h101442">
<CcuId>141705</CcuId>
<EnclosingHireIds>
<EnclosingHireId distance="1">b2</EnclosingHireId>
<EnclosingHireId distance="2">a1</EnclosingHireId>
</EnclosingHireIds>
<OrgNo>123456789</OrgNo>
<GlnLocation>1234567890123</GlnLocation>
<StartDate>2013-10-09</StartDate>
<EndDate>2013-11-08</EndDate>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="get" rel="self"/>
<Link href="/ccus/141705" method="get" rel="Ccu"/>
<Link href="/ccus/141705/hires/a1" method="get" rel="EnclosingHire"/>
<Link href="/organizations/123456789" method="get" rel="Organization"/>
<Link href="/organizations/123456789/locations/1234567890123" method="get" rel="Location"/>
<Link href="/ccus/141705/hires/a1/hires/h101442/documents" method="post" rel="Documents"/>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="put" rel="update"/>
<Link href="/ccus/141705/hires/a1/hires/h101442/hires" method="post" rel="addHire"/>
</Hire>

26. Eksempel: Hire i EPIM LogisticsHub
26
<Hire id="h101442">
<CcuId>141705</CcuId>
<EnclosingHireIds>
<EnclosingHireId distance="1">b2</EnclosingHireId>
<EnclosingHireId distance="2">a1</EnclosingHireId>
</EnclosingHireIds>
<OrgNo>123456789</OrgNo>
<GlnLocation>1234567890123</GlnLocation>
<StartDate>2013-10-09</StartDate>
<EndDate>2013-11-08</EndDate>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="get" rel="self"/>
<Link href="/ccus/141705" method="get" rel="Ccu"/>
<Link href="/ccus/141705/hires/a1" method="get" rel="EnclosingHire"/>
<Link href="/organizations/123456789" method="get" rel="Organization"/>
<Link href="/organizations/123456789/locations/1234567890123" method="get" rel="Location"/>
<Link href="/ccus/141705/hires/a1/hires/h101442/documents" method="post" rel="Documents"/>
<Link href="/ccus/141705/hires/a1/hires/h101442" method="put" rel="update"/>
<Link href="/ccus/141705/hires/a1/hires/h101442/hires" method="post" rel="addHire"/>
</Hire>

27. HATEOAS
27
●
Bruker mye båndbredde
●
For å kunne slippe å refaktorere
noe som er lett å refaktorere
●
Og som nesten aldri endrer seg
●
YAGNI (You aren't gonna need it)