The never ending REST API design debate

What should a good REST API look like? Should you use verbs or nouns in your resource paths? How do you handle versioning of APIs? How to deal with partial responses and pagination? Which status codes should I make use of? What about sorting, filtering, and searching? Have you thought about content negotiation, and hypermedia?

Guillaume will got through all these topics, offering advice on the best approaches to those questions, and opening up the debate on the various options available, so as to make your Web API at REST, as clean and elegant as possible.

Transcript

1. The never-ending REST API design debate Guillaume Laforge Restlet — the Web API platform Chair of the Apache Groovy PMC @glaforge
2. We know about APIs! http://restlet.com
3. We know about APIs! http://restlet.com
4. ROY FIELDING REST DISSERTATION
5. ROY FIELDING REST DISSERTATION Principled design of the modern Web architecture
6. 4 Representational State Transfer Architectural properties • Performance • Scalability • Simplicity • Modifiability • Visibility • Portability • Reliability Architectural constraints • Client-server • Stateless • Cacheable • Layered system • Code on demand (optional) • Uniform interface
7. 5 REST — Uniform interface • Identification of resources • Manipulation of resources 
 through representations • Self-descriptive messages • HATEOAS 
 (Hypermedia As The Engine 
 Of Application State)
8. 5 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
9. 5 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…
10. 5 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…
11. 5 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…
12. 6 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 Replace or create an individual car Delete all the cars Delete an individual car
13. NOUNS ARE GOOD VERBS ARE BAD
14. 8 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
16. 10 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’
17. Camel case?
18. Camel case? Snake case!
19. 12 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!
20. 13 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
21. API PARAMETERS RULE OF THUMBS
22. 15 API parameters — rule of thumbs • Path • required, resource identifier • Query • optional, query collections • Body • resource specific logic • Header • global, platform-wide
23. 16 HTTP Status Code Map http://bit.ly/stcode
24. 17 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 :-(
25. 18 Common HTTP Status Codes — 1xx
26. 19 Common HTTP Status Codes — 2xx
27. 19 Common HTTP Status Codes — 2xx
28. 19 Common HTTP Status Codes — 2xx
29. 19 Common HTTP Status Codes — 2xx
30. 19 Common HTTP Status Codes — 2xx
31. 19 Common HTTP Status Codes — 2xx
32. NOT JUST 200 201 202 204 206
33. Anti-pattern: returns 200 for everything, even errors!
34. 22 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
35. API navigation is important to make the API more discoverable
36. 24 DHC by Restlet: API testing tool
37. 25 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
38. 26 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
39. 27 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" ...
40. 28 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
41. Caching!
42. 30 Last-Modified GET /users/123 Modified-Since: Fri, 13 Nov 2015 02:13:11 GMT HTTP/1.1 200 OK Last-Modified: Sun, 15 Nov 2015 04:58:08 GMT
43. 31 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
44. PAGINATION
45. 33 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
46. 34 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
47. Wrapped CollectionS
48. 36 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, ... } ]
49. 37 Common HTTP Status Codes — 3xx
50. 37 Common HTTP Status Codes — 3xx
51. 37 Common HTTP Status Codes — 3xx
52. 37 Common HTTP Status Codes — 3xx
53. 37 Common HTTP Status Codes — 3xx
54. 37 Common HTTP Status Codes — 3xx
55. 38 Common HTTP Status Codes — 4xx
56. 38 Common HTTP Status Codes — 4xx
57. 38 Common HTTP Status Codes — 4xx
58. 38 Common HTTP Status Codes — 4xx
59. 38 Common HTTP Status Codes — 4xx
60. 38 Common HTTP Status Codes — 4xx
61. 39 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"] }
62. 40 Common HTTP Status Codes — 5xx
63. 40 Common HTTP Status Codes — 5xx
64. 40 Common HTTP Status Codes — 5xx
65. 40 Common HTTP Status Codes — 5xx
66. 41 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
67. RATE LIMITATION
68. 43 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
69. ONE SIZE FITS ALL Different payloads for different consumers
70. 45 Selecting with query parameters • Only 5 stars Chinese restaurants • GET https://api.co/restaurants?type=chinese&stars=5
71. FIL TERING
72. 47 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
73. 48 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…
74. 49 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 • … • …
75. SORTING
76. 51 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
77. SEARCHING
78. 53 Searching • Combien various filtering fields • Or provide a full-blown query language
79. v1
80. 55 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
81. hypermedia
82. 57 Richardson maturity model
83. 58 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
84. C H A N G E IS U N A V O ID A B L E
85. 60 Lots of choice • HAL • JSON-LD • Collection+JSON • SIREN • … • Which to chose from? • no real consensus yet • but HAL seems quite common
86. 61 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]
87. 62 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
88. HAL I’m sorry Dave, I can do Hypermedia
89. 64 HAL approach GET 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
90. Resources
91. 66 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
92. Thanks for your attention
93. Questions & Answers