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The never-ending REST API design debateGuillaume Laforge Restlet — the Web API platform Chair of the Apache Groovy PMC @glaforge
Devoxx Promo Code: ctwdevoxxfrhttp://www.manning.com/koenig2/
GROOVY IN ACTION 2ND EDITION
ROY FIELDING
REST DISSERTATION
ROY FIELDING
REST DISSERTATION
Principled design of the modern
Web architecture
5
Representational State TransferArchitectural properties
• Performance • Scalability • Simplicity • Modifiability • Visibility • Portability • Reliability
Architectural constraints
• Client-server • Stateless • Cacheable • Layered system • Code on demand (optional) • Uniform interface
6
REST — Uniform interface• Identification of resources
• Manipulation of resources through representations
• Self-descriptive messages
• HATEOAS (Hypermedia As The Engine Of Application State)
6
REST — Uniform interface• Identification of resources
• Manipulation of resources through representations
• Self-descriptive messages
• HATEOAS (Hypermedia As The Engine Of Application State)
Resource as URIs http://api.co/cars/123
6
REST — Uniform interface• Identification of resources
• Manipulation of resources through representations
• Self-descriptive messages
• HATEOAS (Hypermedia As The Engine Of Application State)
Resource as URIs http://api.co/cars/123
JSON, XML…
6
REST — Uniform interface• Identification of resources
• Manipulation of resources through representations
• Self-descriptive messages
• HATEOAS (Hypermedia As The Engine Of Application State)
Resource as URIs http://api.co/cars/123
JSON, XML…
HTTP GET, POST, PUT, DELETE media types, cacheability…
6
REST — Uniform interface• Identification of resources
• Manipulation of resources through representations
• Self-descriptive messages
• HATEOAS (Hypermedia As The Engine Of Application State)
Resource as URIs http://api.co/cars/123
JSON, XML…
HTTP GET, POST, PUT, DELETE media types, cacheability…
Hypermedia APIs HAL, JSON-LD, Siren…
7
HTTP methods / URIs for collection/item
GET
POST
PUT
DELETE
http://api.co/v2/cars/ http://api.co/v2/cars/1234
List all the cars Retrieve an individual car
Create a new car Error
Replace the entire collection with a whole new list of cars Update an individual car
Delete all the cars Delete an individual car
NOUNS
ARE GOOD
VERBS
ARE BAD
9
Nouns are good, verbs are bad!• Prefer nouns to verbs
• nouns refer to resources • resources are handled with HTTP verbs
• Verbs can be used for actions or calculations • /login, /logout • /convertTemperature • /repositories/123/star
11
Singular or plural resources?• Prefer plural forms
• /tickets/234 vs /ticket/234
• Avoid confusing odd singular vs plural forms • /person vs /people, or /goose vs /geese • Easier for URL routing (same prefix) • Think of it as:
‘This is the 234th item of the tickets collection’
Camel case?
Camel case?
Snake case!
13
Different casing in the wild• UpperCamelCase or lowerCamelCase • snake_case or dashed-snake-case
• Prefer lowercase • Prefer snake_case • Underscores seem more common in APIs
• But chose one casing and be consistent!
14
Dealing with relations in your URLs• /tickets/123/messages/4
• a ticket could be a group of messages
• /usergroups/234/users/67 • a user could belong to different usergroups • user should have a URL of its own, referenced from the
usergroup payload
API PARAMETERS RULE OF THUMBS
16
API parameters — rule of thumbs• Path
• required, resource identifier • Query
• optional, query collections • Body
• resource specific logic • Header
• global, platform-wide
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HTTP Status Code Map http://bit.ly/stcode
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Common HTTP status codes• Use appropriate HTTP status codes when answering
requests:
• 1xx: Hold on… • 2xx: Here you go! • 3xx: Go away! • 4xx: You fucked up :-D • 5xx: I fucked up :-(
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Common HTTP Status Codes — 1xx
20
Common HTTP Status Codes — 2xx
20
Common HTTP Status Codes — 2xx
20
Common HTTP Status Codes — 2xx
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Common HTTP Status Codes — 2xx
20
Common HTTP Status Codes — 2xx
20
Common HTTP Status Codes — 2xx
NOT JUST 200
201
202
204
206
Anti-pattern: returns 200
for everything, even errors!
23
Not just 200 OK! — 201 Created• Specify a Location header, pointing at the location of the
newly created resource
POST /cars ...
HTTP/1.1 201 Created Location: http://cars.co/v2/cars/5959
API navigation is important to make the API more discoverable
25
DHC by Restlet: API testing tool
26
Not just 200 OK! — 202 Accepted• Request accepted but will be handled asynchronously
• a job might be running later and yield a result later on
POST /jobs ...
HTTP/1.1 202 Accepted
No payload returned
27
Not just 200 OK! — 204 No content• The resource was deleted and no payload is returned
• but could return 200 OK & provide the payload of the deleted element
DELETE /tickets/654
HTTP/1.1 204 No content
28
Not just 200 OK! — 206 Partial content• A partial list of meteorites is returned, using pagination
• add a Link header to facilitate navigation
GET /meteorites?page=4
HTTP/1.1 206 Partial content Link: <http://nasa.co/meteorites?page=1>; rel="first", <http://nasa.co/meteorites?page=3>; rel="prev", <http://nasa.co/meteorites?page=5>; rel="next", <http://nasa.co/meteorites?page=9>; rel="last"
...
29
Not just 200 OK! — 304 Not modified• When HTTP caching headers are in play
• the client should have a version in cache already
GET /meteorites/654
HTTP/1.1 304 Not modified
Caching!
31
Last-Modified
GET /users/123 Modified-Since: Wed, 13 Apr 2016 02:13:11 GMT
HTTP/1.1 200 OK Last-Modified: Fri, 15 Apr 2016 04:58:08 GMT
32
ETag
GET /users/123 If-None-Match: a456ef544eeb7333af
HTTP/1.1 200 OK ETag: 686897696a7c876b7e
GET /users/123 If-None-Match: 686897696a7c876b7e
HTTP/1.1 304 Not modified
PAGINATION
34
Pagination with query parameters• With a page number: ?page=23
• can also specify a page size • might get odd results when insertions happen
• With a cursor: ?cursor=34ea3fd6 • insertion-friendly
• With a semantic parameter: ?page=A • interesting when limited / discrete number of pages
35
Pagination with accept range header• Accept range header not just for bytes
GET /users
HTTP/1.1 206 Partial content Accept-Ranges: users Content-Range: users 0-9/200
GET /users Range: users=0-9
Wrapped CollectionS
37
Wrapped collections• Prefer unwrapped collections
• unless there’s specific collection payload metadata(example: photo album details)
• pagination are better in HTTP headers
GET /tickets Content-Type: application/json
{ data: [ { id: 1, ... }, { id: 2, ... } ] }
GET /tickets Content-Type: application/json
[ { id: 1, ... }, { id: 2, ... } ]
38
Common HTTP Status Codes — 3xx
38
Common HTTP Status Codes — 3xx
38
Common HTTP Status Codes — 3xx
38
Common HTTP Status Codes — 3xx
38
Common HTTP Status Codes — 3xx
38
Common HTTP Status Codes — 3xx
39
Common HTTP Status Codes — 4xx
39
Common HTTP Status Codes — 4xx
39
Common HTTP Status Codes — 4xx
39
Common HTTP Status Codes — 4xx
39
Common HTTP Status Codes — 4xx
39
Common HTTP Status Codes — 4xx
40
Provide helpful error payloads• No definitive standard yet
• http problem proposal and vnd-error mime type
HTTP/1.1 403 Forbidden Content-Type: application/problem+json Content-Language: en
{ "type": "https://example.com/probs/out-of-credit", "title": "You do not have enough credit.", "detail": "Your current balance is 30, but that costs 50.", "instance": "/account/12345/msgs/abc", "balance": 30, "accounts": ["/account/12345", "/account/67890"] }
41
Common HTTP Status Codes — 5xx
41
Common HTTP Status Codes — 5xx
41
Common HTTP Status Codes — 5xx
41
Common HTTP Status Codes — 5xx
42
Treating unknown status codes• An unknown status code should be treated
as the first one of the family
• 4xx — 400 generic client error • 5xx — 500 generic server error
RATE LIMITATION
44
Rate limitation
HTTP/1.1 200 OK Date: Mon, 01 Jul 2013 17:27:06 GMT Status: 200 OK X-RateLimit-Limit: 60 X-RateLimit-Remaining: 56 X-RateLimit-Reset: 1372700873
Total number of requests allowed
Number of requests left
remaining window before the rate limit resets in UTC
epoch seconds
ONE SIZE FITS
ALL
Different payloads for different consumers
46
Selecting with query parameters• Only 5 stars Chinese restaurants
• GET https://api.co/restaurants?type=chinese&stars=5
FILTERING
48
Filtering• Specify fields you’re interested in:
• GET https://api.co/users/123?fields=firstname,lastname,age
• Specify excluded fields: • GET https://api.co/users/123?exclude=biography,resume
• Specify a « style »: • GET https://api.co/users/123?style=compact
49
Prefer… the prefer header
GET /users/123 HTTP/1.1 Content-Type: application/json Prefer: return=minimal Vary: Prefer,Accept,Accept-Encoding
HTTP/1.1 200 OK Content-Type: application/json; charset=utf-8 Vary: Prefer,Accept,Accept-Encoding Preference-Applied: return=minimal
Define different profiles: minimal,
mobile, full…
50
Expanding referenced resources• Use the dot notation to explicit you want sub-resources
• GET https://api.co/users/123?fields=address.zip
• user • name • address
• zip • country • …
• …
SORTING
52
Sorting• SQL-style
• GET https://api.co/books?sort=title+DESC • GET https://api.co/books?sort=title+DESC,author+ASC
• Sort + asc/desc combo • GET https://api.co/books?sort=title&desc=title • GET https://api.co/books?
sort=title,author&desc=title&asc=author
SEARCHING
54
Searching• Combine various filtering fields
• Or provide a full-blown query language
55
Search / filter / sort…• Also have a look at other approaches
• Facebook’s GraphQL • Netflix’s Falcor
v1
57
Different approaches for API versioning• Most frequent, in the URL:
• https://api.com/v2/restaurants/1234
• Custom header: • X-API-Version: 2
• Less frequent, with an accept header • clients don’t have to change endpoint, but update headers
GET /restaurants Accept: application/vnd.restaurants.v2+json
hypermedia
59
Richardson maturity model
60
Pros & Cons of hypermedia• Pros
• more generic clients • can palliate the need for API versioning
• Cons • heavier payload (think mobile devices w/ bad connectivity) • clients still need to understand what links are about and
how to represent them in their UI
CHANGE IS
UNAVOID
ABLE
62
Lots of choice• HAL • JSON-LD • Collection+JSON • SIREN • …
• Which to chose from? • no real consensus yet • but HAL seems quite common
63
A word about IDs for linked resources• If you’re tempted to go your own way for hypermedia…
• Be sure to define direct links to resources • photos: [http://news.co/articles/123/photos/654,
http://news.co/articles/123/photos/659]
• Not mere IDs for which API clients need to figure out the exact resource location (error-prone) • photos: [654, 659]
64
Another word about IDs• Usually avoid counter-type IDs: 1, 2, 3, 4…
• Prefer UUIDs • makes it harder for malignant users
to scan & discover existing resources • auto-incrementing IDs might not be unique
in distributed systems
HAL
I’m sorry Dave, I can do Hypermedia
66
HAL approachGET https://api.com/player/1234567890
HTTP/1.1 200 OK
{
"_links": { "self": { "href": "https://api.com/player/1234567890" }, "friends": { "href": "https://api.com/player/1234567890/friends" } }, "playerId": "1234567890", "name": "Kevin Sookocheff", "alternateName": "soofaloofa", "image": "https://api.com/player/1234567890/avatar.png" }
Special _links property
Resources
68
API design resources• http://www.vinaysahni.com/best-practices-for-a-pragmatic-restful-api • https://github.com/paypal/api-standards/blob/master/api-style-guide.md • http://blog.octo.com/en/design-a-rest-api/ • https://github.com/interagent/http-api-design/blob/master/SUMMARY.md • http://sookocheff.com/post/api/on-choosing-a-hypermedia-format/ • http://www.troyhunt.com/2014/02/your-api-versioning-is-wrong-which-is.html
Thanks for your attention
Questions & Answers