REST  APIs    for  the    

Internet  Of  Things  

Michael  J  Koster  Open  Source  Internet  Of  Things  

Meetup  19  March  2014  

Resource  oriented  API  

•  Resource  ==  web  resource  (URI)  •  Resources  change  state  in  response  to  what  is  being  sensed  

•  Actuator  changes  state  in  response  to  web  resource  update  

•  Abstract  data  sources  and  sinks  •  REST  API  has  2  important  characterisJcs  for  IoT  use  case…  

RepresentaJonal  State  Transfer  

•  Resource  interacJon  through  exchange  of  representaJon  of  resource  state  

•  E.g.  a  representaJon  of  the  state  of  a  temperature  sensor  might  be  “63.6”    

•  Convenient  for  applicaJon  soTware  to  use  read/write  semanJcs  to  interact  with  resources  

•  Stateful  resource  representaJons  =>  Stateless  applicaJon  soTware  

Based  on  Hypermedia  

•  Use  of  web  links  to  locate  resources  of  interest  

•  IoT  needs  machine-­‐readable  links  that  enable  applicaJon  soTware  to  discover  things  of  interest  

•  Subset  of  web  linking,  semanJc  web  using  relaJon/a\ribute  

•  Links  encode  metadata  about  the  resource,  e.g.  type=‘temperature’,  ct=‘applicaJon/json’  

Web  Linking  for  IoT  

•  Links  are  managed  in  2  ways  •  Object  encapsulaJon:  self-­‐describing  objects  have  links  associated  with  endpoint,  e.g.  ./well-­‐known/core  

•  Resource  Directory:  Directories  and  Catalogs  of  links,  stored  at  well-­‐known  locaJons,  that  point  to  resources  and  to  other  catalogs  

Web  Linking  for  IoT  

•  Links  can  be  registered  with  a  Resource  Directory  when  sensors  are  brought  online  

•  A  crawler  can  discover  links  at  ./well-­‐known/core  locaJons  and  populate  catalogs  

•  ApplicaJon  soTware  can  discover  resources  by  a\ribute,  e.g.  query  using  type=‘temperature’,  units=‘celsius’,  locaJon=‘outdoor’  etc.    

•  System  returns  a  set  of  links  matching  the  query  a\ributes  

CoAP  

•  Part  of  IPV6  for  Constrained  Resource  Environments  (CoRE)  

•  IoT  oriented  REST  API  mapped  to  an  efficient  binary  protocol  

•  End  devices  can  have  both  client  and  server  roles,  can  also  communicate  directly  

•  Resource  representaJon  e.g.  ‘applicaJon/json’,  is  negoJated  as  in  h\p  protocol  

CoAP  

•  Observe  opJon  for  long-­‐term  event  stream  response  to  GET,  asynchronous  updates  

•  Web  linking  using  IETF  standard  core-­‐link-­‐format  (RFC  6690)  

•  Resource  discovery  using  ./well-­‐known/core  or  external  Resource  Directory  

 

HTTP/REST  

•  HTTP  and  REST  is  useful  for  most  web  applicaJons,  services,  and  gateways  

•  Uses  web  callbacks,  websockets,  HTTP  PUT  for  asynchronous  updates  

•  Links  in  JSON,  Link-­‐format,  Hypercat,  linked  data  

•  Well  defined  CoAP-­‐to-­‐HTTP  proxy  pa\erns,  standard  middleware  

Hybrid  system  

•  It’s  possible  to  use  REST  for  resource  discovery  and  other  stateful  interacJons,  and  messaging  e.g.  MQTT  for  asynchronous  updates  

•  Various  methods  to  bind  message  endpoints  to  REST  resources  

•  ApplicaJon  soTware  can  easily  use  both  REST  API  and  event  handler  interfaces  like  onUpdate  

•  IoT  Toolkit  uses  observers  to  bind    

Standards  and  SoTware  •  CoAP    h\ps://datatracker.iel.org/doc/draT-­‐iel-­‐core-­‐coap/  

•  CoRE  link-­‐format  h\p://tools.iel.org/html/rfc6690  

•  CoRE  Observe  h\ps://datatracker.iel.org/doc/draT-­‐iel-­‐core-­‐observe/  

•  CoRE  Resource  Directory  h\ps://tools.iel.org/html/draT-­‐iel-­‐core-­‐resource-­‐directory-­‐00  

•  Hypercat  h\p://wiki.1248.io/doku.php?id=hypercat  

IoT  Toolkit  Interoperability  Demo  

smartobjectservice.com  

Node-­‐RED  

Node-­‐RED  

MQTT  Observer  

MQTT  Broker  

REST  Endpoint  ObservableProperty  

mq\Observer  

PUT   GET  

Publish  from  data  producer  

Publish  From  REST  API  

Publish  to  Other  Subscribers  

SUB  Publish  to  REST  API    

Connects  REST  Resource  to  MQTT  Topic  Publish  and  Subscribe  

MQTT  Observer  

MQTT  Broker  

REST  Endpoint  ObservableProperty  

mq\Observer  

PUT   GET  

Publish  from  data  producer  

Publish  From  REST  API  

Publish  to  Other  Subscribers  

SUB  Publish  to  REST  API    

Publisher    Publishes  REST  Resource  updates  to  the  broker  

MQTT  Observer  

MQTT  Broker  

REST  Endpoint  ObservableProperty  

mq\Observer  

PUT   GET  

Publish  from  data  producer  

Publish  From  REST  API  

Publish  to  Other  Subscribers  

SUB  Publish  to  REST  API    

Subscriber    Makes  last  published  data  available  at  the  REST  endpoint  

MQTT  Observer  

MQTT  Broker  

REST  Endpoint  ObservableProperty  

mq\Observer  

PUT   GET  

Publish  from  data  producer  

Publish  From  REST  API  

Publish  to  Other  Subscribers  

SUB  Publish  to  REST  API    

Pub+Sub  Repeats  data  updates  in  both  direcJons  

MQTT  Bridge  to  mulJple  REST  endpoints    

MQTT  Broker  

REST  Endpoint  ObservableProperty  

mq\Observer  

PUT   GET  

Publish  from  data  producer  

Publish  to  Other  Subscribers  

REST  Endpoint  ObservableProperty  

mq\Observer  

PUT   GET