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The never-ending REST API design debate

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At the Devoxx 2015 conference in Belgium, Guillaume Laforge, Product Ninja & Advocate at Restlet, presented about the never-ending REST API design debate, covering many topics like HTTP status codes, Hypermedia APIs, pagination/searching/filtering, and more.

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The never-ending REST API design debate

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

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