github.com/nicholasjackson/building-microservices-youtube/currency

Currency Service

The currency service is a gRPC service which provides up to date exchange rates and currency conversion capabilities.

Building protos

To build the gRPC client and server interfaces, first install protoc:

Linux

sudo apt install protobuf-compiler

Mac

brew install protoc

Then install the Go gRPC plugin:

go get google.golang.org/grpc

Then run the build command:

protoc -I protos/ protos/currency.proto --go_out=plugins=grpc:protos/currency

Testing

To test the system install grpccurl which is a command line tool which can interact with gRPC API's

https://github.com/fullstorydev/grpcurl

go install github.com/fullstorydev/grpcurl/cmd/grpcurl

List Services

grpcurl --plaintext localhost:9092 list
Currency
grpc.reflection.v1alpha.ServerReflection

List Methods

grpcurl --plaintext localhost:9092 list Currency        
Currency.GetRate
Currency.SubscribeRates

Method detail for GetRate

grpcurl --plaintext localhost:9092 describe Currency.GetRate

Currency.GetRate is a method:
rpc GetRate ( .RateRequest ) returns ( .RateResponse );

RateRequest detail

grpcurl --plaintext --msg-template localhost:9092 describe .RateRequest    
RateRequest is a message:
message RateRequest {
  string Base = 1 [json_name = "base"];
  string Destination = 2 [json_name = "destination"];
}

Message template:
{
  "Base": "EUR",
  "Destination": "EUR"
}

Execute a request for GetRate

➜ grpcurl --plaintext -d '{"Base": "GBP", "Destination": "USD"}' localhost:9092 Currency/GetRate
{
  "rate": 1.2229967868538965
}

Execute a request for SubscribeRates

The parameter -d @ means that gRPCurl will read the messages from StdIn.

grpcurl --plaintext --msg-template -d @ localhost:9092 Currency/SubscribeRates 

You can send a message to the server using the following payload

{
  "Base": "EUR",
  "Destination": "GBP"
}