consume/return a JSON response when executing flow using Spring boot API - spring

Question

I'm a beginner in corda and I'm trying to execute flows using Spring boot API. When I used:
#PostMapping(value = [ "create-iou" ], produces = [ TEXT_PLAIN_VALUE ] , headers = [ "Content-Type=application/x-www-form-urlencoded" ])
my flow is getting executed (by testing it using insomnia). But When I changed it to
#PostMapping(value = [ "create-iou" ], produces = [ APPLICATION_JSON_VALUE ], headers = [ "Content-Type=application/json" ])
It gives me a 406 not acceptable error: No body returned for response.
Here's the API I've created/copied:
#PostMapping(value = [ "create-iou" ], produces = [ TEXT_PLAIN_VALUE ] , headers = [ "Content-Type=application/x-www-form-urlencoded" ])
fun createIOU(request: HttpServletRequest): ResponseEntity<String> {
val iouValue = request.getParameter("iouValue").toInt()
val partyName = request.getParameter("partyName")
?: return ResponseEntity.badRequest().body("Query parameter 'partyName' must not be null.\n")
if (iouValue <= 0 ) {
return ResponseEntity.badRequest().body("Query parameter 'iouValue' must be non-negative.\n")
}
val partyX500Name = CordaX500Name.parse(partyName)
val otherParty = proxy.wellKnownPartyFromX500Name(partyX500Name) ?: return ResponseEntity.badRequest().body("Party named $partyName cannot be found.\n")
return try {
val signedTx = proxy.startTrackedFlow(::Initiator, iouValue, otherParty).returnValue.getOrThrow()
ResponseEntity.status(HttpStatus.CREATED).body("Transaction id ${signedTx.id} committed to ledger.\n")
} catch (ex: Throwable) {
logger.error(ex.message, ex)
ResponseEntity.badRequest().body(ex.message!!)
}
}
I would like to return something like this:
{
iouValue: 99,
lender: PartyA,
borrower: PartyB
}
When executing the flow using http endpoint.

Answer 1

You need to use the RPC connection libraries provided by Corda:
import net.corda.client.rpc.CordaRPCClient
import net.corda.client.rpc.CordaRPCConnection
Take a look to this example to see how to use them.
You are not showing how your proxy is instantiate, but you need to instantiate a proxy to connect via RPC to the node, like so:
val rpcAddress = NetworkHostAndPort(host, rpcPort)
val rpcClient = CordaRPCClient(rpcAddress)
val rpcConnection = rpcClient.start(username, password)
proxy = rpcConnection.proxy
and once you have the proxy, you can create SpringBoot APIs to call that proxy that makes the RPC calls:
#RestController
#RequestMapping("/")
class StandardController(rpc: NodeRPCConnection) {
private val proxy = rpc.proxy
#GetMapping(value = ["/addresses"], produces = arrayOf("text/plain"))
private fun addresses() = proxy.nodeInfo().addresses.toString()
#GetMapping(value = ["/identities"], produces = arrayOf("text/plain"))
private fun identities() = proxy.nodeInfo().legalIdentities.toString()