Designing HTTP Interfaces and RESTful Web Services (T3CON11 2011-10-08)


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Designing HTTP Interfaces and RESTful Web Services (T3CON11 2011-10-08)

  2. 2. David Zuelke
  3. 3. David Zülke
  4. 4.ünchen_Panorama.JPG
  5. 5. Founder
  6. 6. Lead Developer
  7. 7. @dzuelke
  8. 8. THE OLDEN DAYS Before REST was En Vogue
  9. 9.
  10. 10. along came
  11. 11.  dis is srs SEO bsns
  12. 12. and said
  14. 14. at least if they were
  15. 15. so we had to make URLs "SEO friendly"
  16. 16.
  17. 17. and then things got out of control
  18. 18. because nobody really had a clue
  19. 19.
  20. 20.
  21. 21. oh dear…
  22. 22. THE RISE OF WEB SERVICESOhai, Im ur CEO, I canhaz SOAP API plz, today, kthx?
  23. 23. POST  /soapendpoint.php  HTTP/1.1Host:  localhostContent-­‐Type:  text/xml;  charset=utf-­‐8<?xml  version="1.0"  encoding="UTF-­‐8"?><SOAP-­‐ENV:Envelope  xmlns:SOAP-­‐ENV="">    <SOAP-­‐ENV:Body>        <ns1:getProduct  xmlns:ns1="">            <id>123456</id>        </ns1:getProduct>    </SOAP-­‐ENV:Body></SOAP-­‐ENV:Envelope>HTTP/1.1  200  OKContent-­‐Type:  text/xml;  charset=utf-­‐8<?xml  version="1.0"  encoding="UTF-­‐8"?><SOAP-­‐ENV:Envelope  xmlns:SOAP-­‐ENV="">    <SOAP-­‐ENV:Body>        <ns1:getProductResponse  xmlns:ns1="">            <product>                <id>123456</id>                <name>Red  Stapler</name>                <price>3.14</price>            </product>        </ns1:getProductResponse>    </SOAP-­‐ENV:Body></SOAP-­‐ENV:Envelope>
  24. 24. POST  /soapendpoint.php  HTTP/1.1Host:  localhostContent-­‐Type:  text/xml;  charset=utf-­‐8<?xml  version="1.0"  encoding="UTF-­‐8"?><SOAP-­‐ENV:Envelope  xmlns:SOAP-­‐ENV="">    <SOAP-­‐ENV:Body>        <ns1:getProduct  xmlns:ns1="">            <id>987654</id>        </ns1:getProduct>    </SOAP-­‐ENV:Body></SOAP-­‐ENV:Envelope>HTTP/1.1  500  Internal  Service  ErrorContent-­‐Type:  text/xml;  charset=utf-­‐8<?xml  version="1.0"  encoding="UTF-­‐8"?><SOAP-­‐ENV:Envelope  xmlns:SOAP-­‐ENV="">    <SOAP-­‐ENV:Body>        <SOAP-­‐ENV:Fault>            <faultcode>SOAP-­‐ENV:Server</faultcode>            <faultstring>Unknown  Product  </faultstring>        </SOAP-­‐ENV:Fault>    </SOAP-­‐ENV:Body></SOAP-­‐ENV:Envelope>
  25. 25. SOAP sucks, said everyone
  26. 26. lets build APIs without the clutter, they said
  27. 27. example: the API
  28. 28. POST  /api/talk  HTTP/1.1Host:  joind.inContent-­‐Type:  text/xml;  charset=utf-­‐8<?xml  version="1.0"  encoding="UTF-­‐8"?><request>                <auth>                                <user>Chuck  Norris</user>                                <pass>roundhousekick</pass>                </auth>                <action  type="getdetail">                                <talk_id>42</talk_id>                </action></request>HTTP/1.1  200  OKContent-­‐Type:  text/xml;  charset=utf-­‐8<?xml  version="1.0"  encoding="UTF-­‐8"?><response>   <item>     <talk_title>My  Test  Talk</talk_title>     <talk_desc>This  is  a  sample  talk  description</talk_desc>     <ID>42</ID>   </item></response>
  29. 29. PROBLEMS WITH THIS API• Always a POST• Doesnt use HTTP Authentication• Operation information is enclosed in the request ("getdetail")• Nothing there is cacheable• Everything through one endpoint (/api/talks for talks)
  30. 30. Level 0 in the Richardson Maturity Model: Plain old XML over the wire in an RPC fashion
  31. 31. Room for improvement: use one URI for each resource.
  32. 32. That would be Level 1 in Richardsons Maturity Model
  33. 33. Level 0 and Level 1 are a bag of hurt. Do not use them. Ever.
  35. 35. that was awesome
  36. 36. because everyone could say
  37. 37.  I haz REST nao
  38. 38. when in fact
  39. 39. they bloody didn’t
  40. 40. RESTWhat Does That Even Mean?
  41. 41. REpresentational State Transfer
  42. 42. Roy Thomas Fielding: Architectural styles andthe design of network based software architectures.
  43. 43. REST CONSTRAINTS• Client-Server• Stateless• Cacheable• Layered System• Code on Demand (optional)• Uniform Interface
  44. 44. Simple explaination of the Uniform Interface
  45. 45. •A URL identifies a Resource• The URLs have an implicit hierarchy • so you know that something with additional slashes is a subordinate resource (HTTP spec)• Methods perform operations on resources• The operation is implicit and not part of the URL•A hypermedia format is used to represent the data• Link relations are used to navigate a service
  46. 46. a web page is not a resource
  47. 47. it is a (complete) representation of a resource
  48. 48. GETTING JSON BACKGET  /products/  HTTP/1.1Host:  acme.comAccept:  application/jsonHTTP/1.1  200  OKContent-­‐Type:  application/json;  charset=utf-­‐8Allow:  GET,  POST[    {        id:  1234,        name:  "Red  Stapler",        price:  3.14,        location:  ""    }]
  49. 49. GETTING XML BACKGET  /products/  HTTP/1.1Host:  acme.comAccept:  application/xmlHTTP/1.1  200  OKContent-­‐Type:  application/xml;  charset=utf-­‐8Allow:  GET,  POST<?xml  version="1.0"  encoding="utf-­‐8"?><products  xmlns="urn:com.acme.products"  xmlns:xl="">    <product  id="1234"  xl:type="simple"  xl:href="">        <name>Red  Stapler</name>        <price  currency="EUR">3.14</price>    </product></products>
  50. 50. no hypermedia formats yet in those examples!
  51. 51. I will show that in a few minutes
  52. 52. AND FINALLY, HTMLGET  /products/  HTTP/1.1Host:  acme.comAccept:  application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,*/*;q=0.5User-­‐Agent:  Mozilla/5.0  (Macintosh;  U;  Intel  Mac  OS  X  10_5_8;  en-­‐us)  AppleWebKit…HTTP/1.1  200  OKContent-­‐Type:  text/html;  charset=utf-­‐8Allow:  GET,  POST<html  lang="en">    <head>        <meta  http-­‐equiv="Content-­‐Type"  content="text/html;  charset=UTF-­‐8"></meta>        <title>ACME  Inc.  Products</title>    </head>    <body>        <h1>Our  Incredible  Products</h1>        <ul  id="products">            <li><a  href="">Red  Stapler</a>  (€3.14)</li>        </ul>    </body></html>
  53. 53. VOLUME ONEDesigning an HTTP Interface
  54. 54. A FEW EXAMPLESLet’s Start With Proper URL Design
  55. 55. BAD URLS••• WTF?• new what?• sausage ID?•
  56. 56. GOOD URLS a list of products• filtering is a query• a single product• all photos•••
  57. 57. now heres the ironic part
  58. 58. URLs dont matter once you have a fully RESTful interface
  59. 59. but it helps to think in terms of resources
  60. 60. THE NEXT LEVELTime To Throw CRUD Into The Mix
  61. 61. COLLECTION OPERATIONS• • GET to retrieve a list of products • POST to create a new product • returns • 201 Created • Location:
  62. 62. ITEM OPERATIONS• • GET to retrieve • PUT to update • DELETE to, you guessed it, delete
  63. 63. but please
  64. 64. dont let the server maintain client state (e.g. cookies)
  65. 65. Now we are at Level 2 in RMM
  66. 66. RMM LEVEL 2• Use HTTP verbs • GET (safe and idempotent) • POST (unsafe, not idempotent) • PUT & DELETE (unsafe, idempotent)• Use HTTP status codes to indicate result success • e.g. HTTP/1.1 409 Conflict
  67. 67. TWITTERS “REST” API, DISSECTED(well, not the whole API; just the status methods will do)
  68. 68. mind you were not even inspecting the RESTfulness
  69. 69. were just looking at Twitters API from an HTTP perspective
  70. 70. STATUSES/SHOW• GET• Problems: • Operation (“show”) included in the URL • Status ID not a child of the “statuses” collection• Better: GET with Accept header
  71. 71. STATUSES/UPDATE• POST• Problems: • Operation (“update”) included in the URL • Uses the authenticated user implicitly• Better: POST
  72. 72. STATUSES/DESTROY• POST• Problems: • Operation (“destroy”) included in the URL like it’s 1997 • Odd, illogical hierarchy again • Allows both “POST” and “DELETE” as verbs• Better: DELETE
  73. 73. STATUSES/RETWEETS• GET• Problems: • Hierarchy is wrong• Better: GET
  74. 74. STATUSES/RETWEET• PUT• Problems: • “retweets” collection exists, but is not used here • As usual, the action is in the URL (“make retweet” is RPC-y) • Allows both “PUT” and “POST” as verbs• Better: POST
  75. 75. SUMMARY• • POST to create a new tweet• • DELETE deletes, PUT could be used for updates• • POST creates a new retweet
  76. 76. ANGRY GERMAN SUMMARY• Twitters "REST" API sucks, hates HTTP and kills baby kittens.
  77. 77. INTERMISSIONWhats the Biggest Reason for the Success of the Web?
  78. 78. WWW
  79. 79. first data exchange system
  80. 80. planetary scale
  81. 81. why is that possible?
  82. 82. Hyperlinks!
  83. 83. the web has no tight coupling
  84. 84. or a notification infrastructure
  85. 85. that limits scalability
  86. 86. the web embraces failure
  87. 87. its loosely coupled by design
  88. 88. HTTP/1.1 404 Not Found
  89. 89. a link can die, others may still work
  90. 90. links are the exclusive mechanism to navigate the web
  91. 91. adding information to the web doesnt increase friction
  92. 92. (other than being able to find it)
  93. 93. the WWW is the biggest application of the Internet because it is protocol-centric
  94. 94. VOLUME TWORESTful Services with Hypermedia
  95. 95. THE UNIFORM INTERFACE• Identification of Resources (e.g. through URIs) • Representations are conceptually separate!• Manipulation Through Representations (i.e. they are complete)• Self-Descriptive Messages (containing all information)• Hypermedia As The Engine Of Application State ("HATEOAS") magic awesomesauce essential to REST
  96. 96. HATEOASThe Missing Piece in the Puzzle
  97. 97. ONE LAST PIECE IS MISSING• How does a client know what to do with representations?• How do you go to the “next” operation?• What are the URLs for creating subordinate resources?• Where is the contract for the service?
  98. 98. HYPERMEDIA AS THE ENGINE OF APPLICATION STATE• Use links to allow clients to discover locations and operations• Link relations are used to express the possible options• Clients do not need to know URLs, so they can change• The entire application workflow is abstracted, thus changeable• The hypermedia type itself could be versioned if necessary• No breaking of clients if the implementation is updated!
  99. 99. XHTML and Atom are Hypermedia formats
  100. 100. Or you roll your own...
  101. 101. A CUSTOM MEDIA TYPEGET  /products/1234  HTTP/1.1 Remind clients ofHost:  acme.comAccept:  application/ Uniform Interface :) re-use Atom forHTTP/1.1  200  OKContent-­‐Type:  application/;  charset=utf-­‐8 link relationsAllow:  GET,  PUT,  DELETE<?xml  version="1.0"  encoding="utf-­‐8"?><product  xmlns="urn:com.acme.prods"  xmlns:atom="">    <id>1234</id>    <name>Red  Stapler</name>    <price  currency="EUR">3.14</price>    <atom:link  rel="payment"  type="application/vnd.acmecorpshop+xml"                          href=""/></product> meaning defined in IANA Link Relations list
  102. 102. boom, RMM Level 3
  103. 103. XML is really good for hypermedia formats
  104. 104. (hyperlinks, namespaced attributes, re-use of formats, …)
  105. 105. JSON is more difficult
  106. 106. (no hyperlinks, no namespaces, no element attributes)
  107. 107. XML VERSUS JSON<?xml  version="1.0"  encoding="utf-­‐8"?><product  xmlns="urn:com.acme.prods"  xmlns:atom="">    <id>1234</id>    <name>Red  Stapler</name>    <price  currency="EUR">3.14</price>    <atom:link  rel="payment"  type="application/"                          href=""/></product>{    id:  1234,    name:  "Red  Stapler",    price:  {        amount:  3.14,        currency:  "EUR"    },    links:  [        {            rel:  "payment",            type:  "application/",            href:  ""        }    ]}
  108. 108. also, JSON is hard to evolve without breaking clients
  109. 109. <?xml  version="1.0"  encoding="utf-­‐8"?><products  xmlns="">    <product  id="123">        <name>Bacon</name>        <price>5.99</price>    </product></products>
  110. 110. <?xml  version="1.0"  encoding="utf-­‐8"?><products  xmlns="">    <product  id="123">        <name>Bacon</name>        <price>5.99</price>        OMNOMNOM  Bacon    </product></products>
  111. 111. <?xml  version="1.0"  encoding="utf-­‐8"?><products  xmlns="">    <product  id="123">        <name>Bacon</name>        <price>5.99</price>        <price  currency="EUR">4.49</price>    </product></products>
  112. 112. <?xml  version="1.0"  encoding="utf-­‐8"?><products  xmlns="">    <product  id="123">        <name  xml:lang="en">Bacon</name>        <name  xml:lang="de">Speck</name>        <price>5.99</price>    </product></products>
  113. 113. <?xml  version="1.0"  encoding="utf-­‐8"?><products  xmlns="">    <product  id="123">        <name  xml:lang="en">Bacon</name>        <name  xml:lang="de">Speck</name>        <price>5.99</price>        <link  rel="category"  href="..."  />    </product></products>
  114. 114. and hey
  115. 115. without hypermedia, your HTTP interface is not RESTful
  116. 116. that’s totally fineand sometimes even the only way to do it
  117. 117. (e.g. CouchDB or S3 are never going to be RESTful)
  118. 118. just avoid calling it a "REST API" :)
  119. 119. one more hypermedia format example: the Lovefilm API
  120. 120. <?xml  version="1.0"  encoding="utf-­‐8"  standalone="yes"?><search>    <total_results>6</total_results>    <items_per_page>2</items_per_page>    <start_index>1</start_index>    <link  href=";items_per_page=2&amp;term=old"                rel="self"  title="self"/>    <link  href=";items_per_page=2&amp;term=old"                rel="next"  title="next"/>    <link  href=";items_per_page=2&amp;term=old"                rel="last"  title="last"/>    <catalog_title>        <can_rent>true</can_rent>        <release_date>2003-­‐09-­‐12</release_date>        <title  full="Star  Wars:  Knights  of  the  Old  Republic"  clean="Star  Wars:  Knights  of  the  Old  Republic"/>        <id></id>        <adult>false</adult>        <number_of_ratings>574</number_of_ratings>        <rating>4</rating>        <category  scheme=""  term="games"/>        <category  scheme=""  term="Xbox"/>        <category  scheme=""  term="Adventure"/>        <category  scheme=""  term="Role-­‐playing"/>        <category  scheme=""  term="TBC"/>        <link  href=""                    rel=""  title="synopsis"/>        <link  href=""                    rel=""  title="reviews"/>        <link  href="­‐Star-­‐Wars-­‐Knights-­‐of-­‐the-­‐Old-­‐Republic.html?cid=LFAPI"                    rel="alternate"  title="web  page"/>    </catalog_title></search>
  121. 121. ROOM FOR IMPROVEMENT IN THE LOVEFILM API• Uses application/xml instead of a custom media type • Once that is fixed, all the link elements could also have a “type” attribute indicating the media type• Shoulduse XML namespaces on the root element, with one namespace per type (e.g. “urn:com.lovefilm.api.item”, “urn:com.lovefilm.api.searchresult” and so on) • That way, clients can determine the resource type easily
  122. 122. HOSTS AND VERSIONING• Q: Why not ? • A: Because and http:// would be different resources!• Q: What about /1/ or /2/ for versioning? • A: Again, different resources. Instead, use the media type: application/ or application/;ver=2
  123. 123. Also, imagine every install of phpBB or TYPO3 had an API
  124. 124. If the version is in the URL, clients need to regex those
  125. 125.
  126. 126.
  127. 127. that would be fail
  128. 128. or what if another forum software wants the same API?
  129. 129. also would have to use “/v1/” in their URLs
  130. 130. URI based versioning kills interoperability
  131. 131. YOU MIGHT BE WONDERING Why Exactly Is This Awesome?
  132. 132. THE MERITS OF REST• Easyto evolve: add new • Easyto implement: build it features or elements without on top of HTTP, and profit! breaking BC • Authentication & TLS• Easy to learn: developers can "browse" service via link rels • Caching & Load Balancing• Easyto scale up: grows well • Conditional Requests with number of features, users and servers • Content Negotiation
  133. 133. but...
  134. 134. hold on, you say
  135. 135. a plain HTTP-loving service does the job, you say
  136. 136. surely, there is a merit to REST beyond extensibility, you ask
  137. 137. nope
  138. 138. "REST is software design on the scale of decades: everydetail is intended to promote software longevity andindependent evolution. Many of the constraints aredirectly opposed to short-term efficiency. Unfortunately,people are fairly good at short-term design, and usuallyawful at long-term design." Roy Fielding
  139. 139. "Most of RESTs constraints are focused on preservingindependent evolvability over time, which is onlymeasurable on the scale of years. Most developerssimply dont care what happens to their product yearsafter it is deployed, or at least they expect to be aroundto rewrite it when such change occurs." Roy Fielding
  140. 140. FURTHER READING• Ryan Tomayko How I Explained REST to my Wife• Jim Webber, Savas Parastatidis & Ian Robinson How to GET a Cup of Coffee• Roy Thomas Fielding Architectural Styles and the Design of Network-based Software Architectures
  141. 141. BOOKS ON REST• Jim Webber, Savas Parastatidis, Ian Robinson REST in Practice ISBN: 978-0596805821• Subbu Allamaraju RESTful Web Services Cookbook ISBN: 978-0596801687• Leonard Richardson, Sam Ruby RESTful Web Services ISBN: 978-0596529260
  142. 142. !e End
  143. 143. Questions?
  144. 144. THANK YOU! This was a presentation by @dzuelkeSend me questions or hire