Before following this tutorial, make sure you’ve installed

• Docker (https://www.docker.com/)
• Metamask (https://metamask.io)

You will need a private-public key pair to register your service in SNET. Generate them in Metamask before you start this tutorial.

Run this tutorial from a bash terminal.

We’ll use Go gRPC, for more details see https://grpc.io/docs/

In this tutorial we’ll create a Go service and publish it in SingularityNET.

Step 1

Setup a ubuntu:18.04 docker container (with current SNET Daemon version) using provided Dockerfile.

docker build \
    --build-arg language=go \
    -t snet_go_service https://github.com/singnet/dev-portal.git#master:/tutorials/docker

ETCD_HOST=$HOME/.snet/etcd/example-go-service/
ETCD_CONTAINER=/opt/singnet/etcd/
docker run -p 7000:7000 -v $ETCD_HOST:$ETCD_CONTAINER -ti snet_go_service bash

From this point we follow the tutorial in the Docker container’s prompt.

cd dev-portal/tutorials/go

Step 2

Create the skeleton structure for your service’s project

./create_project.sh PROJECT_NAME ORGANIZATION_ID SERVICE_ID SERVICE_PORT

PROJECT_NAME is a short tag for your project. It will be used to name project’s directory and as a namespace tag in the .proto file.

ORGANIZATION_ID is the id of an organization that you are a member or owner.

SERVICE_ID is the id of your service.

SERVICE_PORT is the port number (in localhost) the service will listen to.

create_project.sh will create a directory named PROJECT_NAME with a basic empty implementation of the service.

In this tutorial we’ll implement a service with two methods:

• int div(int a, int b)
• string check(int a)

So we’ll use this command line to create project’s skeleton

./create_project.sh tutorial my-org math-operations 7070
cd /opt/singnet/go/src/tutorial

Step 3

Now we’ll customize the skeleton code to actually implement our basic service. We need to edit ./service_spec/tutorial.proto and define

• the data structures used to carry input and output of the methods, and
• the RPC API of the service.

Take a look at https://developers.google.com/protocol-buffers/docs/overview to understand everything you can do in the .proto file.

In this tutorial our ./service_spec/tutorial.proto will be like this:

syntax = "proto3";

package tutorial;

message IntPair {
    int32 a = 1;
    int32 b = 2;
}

message SingleInt {
    int32 v = 1;
}

message SingleString {
    string s = 1;
}

service ServiceDefinition {
    rpc div(IntPair) returns (SingleInt) {}
    rpc check(SingleInt) returns (SingleString) {}
}

Each message statement define a data structure used either as input or output in the API. The service statement defines the RPC API itself.

Step 4

In order to actually implement our API we need to edit server.go.

Look for SERVICE_API and replace doSomething() by our actual API methods:

func (s *server) Div(ctx context.Context, in *pb.IntPair) (*pb.SingleInt, error) {
	return &pb.SingleInt{V: in.A / in.B}, nil
}
func (s *server) Check(ctx context.Context, in *pb.SingleInt) (*pb.SingleString, error) {
	return &pb.SingleString{S: fmt.Sprintf("%v", in.V)}, nil
}

Step 5

Now we’ll write a client to test our server locally (without using the Blockchain). Edit client.go.

Look for TEST_CODE and replace doSomething() implementation by our testing code:

func doSomething(conn *grpc.ClientConn) (*pb.SingleInt, error) {
	// Check the compiled proto file (.pb.go) to get this method name
	c := pb.NewServiceDefinitionClient(conn)
	// Set variables 'a' and 'b' to be sent to the server.
	var a int32 = 12
	var b int32 = 4
	if len(os.Args) > 2 {
		if i, err := strconv.ParseInt(os.Args[1], 10, 32); err == nil {
			a = int32(i)
		}
		if i, err := strconv.ParseInt(os.Args[2], 10, 32); err == nil {
			b = int32(i)
		}
	}
	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
	defer cancel()
	r, err := c.Div(ctx, &pb.IntPair{A: a, B: b})
	if err != nil {
		return nil, err
	} else {
	    return r, nil
    }
}

Step 6

To compile the protobuf file:

./build.sh

Step 7

To test our server locally (without using the Blockchain)

./server &
./client 12 4

You should have something like the following output:

./server &

# [1] 4217
# Server listening on 0.0.0.0:7070

./client 12 4
# 3

At this point you have successfully built a gRPC Go service. The executables can be used from anywhere inside the container (they don’t need anything from the installation directory) or outside the container if you have Go gRPC libraries installed.

The next steps in this tutorial will publish the service in SingularityNET.

Step 8

Now you must follow the publish tutorial to publish this service or use our script (next step).

You’ll also need a SNET CLI identity (check step 3 from publish tutorial).

Step 9

First, make sure you killed the server process started in Step 7.

Then publish and start your service:

./publishAndStartService.sh PAYMENT_ADDRESS

Replace PAYMENT_ADDRESS by your public key (wallet).

Example:

./publishAndStartService.sh 0x501e8c58E6C16081c0AbCf80Ce2ABb6b3f91E717

This will start the SNET Daemon and your service. If everything goes well you will see the Blockchain transaction logs and then the following messages (respectively from: your service and SNET Daemon):

# [Blockchain log]
# Server listening on 0.0.0.0:7070
# [daemon initial log]
# INFO[0002] Blockchain is enabled: instantiate payment validation interceptor 
# INFO[0002]                                               PaymentChannelStorageClient="&{ConnectionTimeout:5s RequestTimeout:3s Endpoints:[http://127.0.0.1:2379]}"
# INFO[0002] Default payment handler registered            defaultPaymentType=escrow
# DEBU[0002] starting daemon                              

You can double check if it has been properly published using

snet organization list-services my-org

Optionally you can un-publish the service

snet service delete my-org math-operations

Actually, since this is just a tutorial, you are expected to un-publish your service as soon as you finish the tests.

Other snet commands and options (as well as their documentation) can be found here.

Step 10

You can test your service making requests in command line:

The openChannel.sh script will open and initialize a new payment channel, it’ll output the new channel id (that will be used by testServiceRequest.sh):

./openChannel.sh

# [Blockchain log]
# #channel_id
# 10

In this example the channel id is 10.

Now you can run testServiceRequest.sh VALUE_A VALUE_B:

./testServiceRequest.sh 12 4

# [Blockchain log]
#   response:
#       v: 3

That’s it. Remember to delete your service as explained in Step 9.

snet service delete my-org math-operations

Last modified on : 15-Oct-24