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
   

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2. We know
   about
   APIs!
   http://restlet.com
   

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3. We know
   about
   APIs!
   http://restlet.com
   

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4. ROY FIELDING
   REST
   DISSERTATION
   

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5. ROY FIELDING
   REST
   DISSERTATION
   Principled design
   of the modern
   Web architecture
   

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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
   

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7. 5
   REST — Uniform interface
   • Identification of resources
   • Manipulation of resources 

   through representations
   • Self-descriptive messages
   • HATEOAS 

   (Hypermedia As The Engine 

   Of Application State)
   

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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
   

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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…
   

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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…
    

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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…
    

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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
    

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13. NOUNS
    ARE GOOD
    VERBS
    ARE BAD
    

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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
    

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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’
    

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17. Camel
    case?
    

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18. Camel
    case?
    Snake
    case!
    

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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!
    

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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
    

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21. API PARAMETERS
    RULE OF THUMBS
    

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22. 15
    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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23. 16
    HTTP Status Code Map http://bit.ly/stcode
    

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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 :-(
    

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25. 18
    Common HTTP Status Codes — 1xx
    

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26. 19
    Common HTTP Status Codes — 2xx
    

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27. 19
    Common HTTP Status Codes — 2xx
    

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28. 19
    Common HTTP Status Codes — 2xx
    

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29. 19
    Common HTTP Status Codes — 2xx
    

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30. 19
    Common HTTP Status Codes — 2xx
    

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31. 19
    Common HTTP Status Codes — 2xx
    

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32. NOT
    JUST
    200
    201
    202
    204
    206
    

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33. Anti-pattern:
    returns 200
    for everything,
    even errors!
    

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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
    

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35. API navigation is
    important to make the
    API more discoverable
    

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36. 24
    DHC by Restlet: API testing tool
    

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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
    

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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
    

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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: ; rel="first", 

    ; rel="prev",
    ; rel="next", 

    ; rel="last"
    ...
    

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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
    

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41. Caching!
    

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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
    

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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
    

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44. PAGINATION
    

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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
    

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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
    

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47. Wrapped
    CollectionS
    

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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, ... }
    ]
    

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49. 37
    Common HTTP Status Codes — 3xx
    

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50. 37
    Common HTTP Status Codes — 3xx
    

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51. 37
    Common HTTP Status Codes — 3xx
    

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52. 37
    Common HTTP Status Codes — 3xx
    

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53. 37
    Common HTTP Status Codes — 3xx
    

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54. 37
    Common HTTP Status Codes — 3xx
    

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55. 38
    Common HTTP Status Codes — 4xx
    

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56. 38
    Common HTTP Status Codes — 4xx
    

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57. 38
    Common HTTP Status Codes — 4xx
    

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58. 38
    Common HTTP Status Codes — 4xx
    

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59. 38
    Common HTTP Status Codes — 4xx
    

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60. 38
    Common HTTP Status Codes — 4xx
    

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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"]
    }
    

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62. 40
    Common HTTP Status Codes — 5xx
    

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63. 40
    Common HTTP Status Codes — 5xx
    

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64. 40
    Common HTTP Status Codes — 5xx
    

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65. 40
    Common HTTP Status Codes — 5xx
    

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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
    

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67. RATE
    LIMITATION
    

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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
    

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69. ONE
    SIZE
    FITS
    ALL
    Different payloads
    for different
    consumers
    

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70. 45
    Selecting with query parameters
    • Only 5 stars Chinese restaurants
    • GET https://api.co/restaurants?type=chinese&stars=5
    

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71. FIL
    TERING
    

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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
    

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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…
    

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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
    • …
    • …
    

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75. SORTING
    

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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
    

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77. SEARCHING
    

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78. 53
    Searching
    • Combien various filtering fields
    • Or provide a full-blown query language
    

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79. v1
    

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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
    

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81. hypermedia
    

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82. 57
    Richardson maturity model
    

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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
    

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84. C
    H
    A
    N
    G
    E
    IS
    U
    N
    A
    V
    O
    ID
    A
    B
    L
    E
    

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85. 60
    Lots of choice
    • HAL
    • JSON-LD
    • Collection+JSON
    • SIREN
    • …
    • Which to chose from?
    • no real consensus yet
    • but HAL seems quite common
    

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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]
    

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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
    

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88. HAL
    I’m sorry Dave, I
    can do Hypermedia
    

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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
    

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90. Resources
    

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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
    

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92. Thanks for your attention
    

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93. Questions & Answers
    

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