Algorithm 4 Responding to a service request using the service broker.

Require:

B:   Global state of the blockchain.

P:   Service broker smart contract caller.

$I_{req}$:    UUID of the request to which the response answers.

$T_{res}$: Date and time when the response is created.

$U_{res}$:   The request processing status.

$R_{res}$:   Optional value to be returned to the service request sender.

Ensure:

Service request information is saved in the blockchain.

1: if $WRITE\notin$ GetCallerPermissions $\left(P\right)$ then

2:  return error      ▹ Abort if caller is not allowed to update the blockchain

3: end if

4: if GetService $(I_{org},I_{dev},N_{srv})=\varnothing$ then

5:  return error             ▹ Abort if requested service is not registered

6: end if

7: $S_{req}=$ GetServiceRequest $\left(I_{req}\right)$

8: if $S_{req}=\varnothing$ then

9:  return error               ▹ Abort if service request does not exist

10: end if

11: if GetDeviceId $\left(S_{req}\right)\ne$ GetContractCallerId $\left(P\right)$ then

12:  return error            ▹ Abort if caller impersonates another device

13: end if

14: if GetOrganizationId $\left(S_{req}\right)\ne$ GetContractCallerOrgId $\left(P\right)$ then

15:  return error      ▹ Abort if caller impersonates another organization

16: end if

17: $S_{res}\leftarrow$ Serialize $(I_{req},T_{res},U_{res},R_{res})$

18: $B\left[I_{req}\right]\leftarrow \{S_{req},S_{res}\}$

19: NotifyEvent $\left(S_{res}\right)$

20: return $S_{res}$