How to Write a SingularityNET Service in C++

Getting started with C++ for your AI Service

Back to tutorials How to Write a SingularityNET Service in Go

Before following this tutorial, make sure you’ve installed

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 C++ gRPC, for more details see https://grpc.io/docs/

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

Step 1

Setup and run a docker container. We’ll install C++ gRPC stuff in a container because of this warning from the authors:

"WARNING: After installing with make install there is no easy way to uninstall,
which can cause issues if you later want to remove the grpc and/or protobuf
installation or upgrade to a newer version."

In this tutorial we’ll develop our service inside the docker container.

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

SNETD_VERSION="v0.1.7"
docker build \
    --build-arg language=cpp \
    --build-arg snetd_version=$SNETD_VERSION \
    -t snet_cpp_service https://github.com/singnet/dev-portal.git#master:/tutorials/docker

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

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

cd dev-portal/tutorials/cpp

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 snet math-operations 7070
cd tutorial

Step 3

Now we’ll customize the skeleton code to actually implement our basic service. We need to edit src/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 src/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 src/server.cc.

Look for PROTO_TYPES and replace the using statements to reflect our data types defined in step 3.

using tutorial::ServiceDefinition;
using tutorial::IntPair;
using tutorial::SingleInt;
using tutorial::SingleString;

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

Status div(ServerContext* context, const IntPair* input, SingleInt* output) override {
    output->set_v(input->a() / input->b());
    return Status::OK;
}

Status check(ServerContext* context, const SingleInt* input, SingleString* output) override {
    if (input->v() != 0) {
        output->set_s("OK");
    } else {
        output->set_s("NOK");
    }
    return Status::OK;
}

Step 5

Now we’ll write a client to test our server locally (without using the blockchain). Edit src/client.cc.

Look for PROTO_TYPES and replace the using statements to reflect our data types defined in Step 3.

using tutorial::ServiceDefinition;
using tutorial::IntPair;
using tutorial::SingleInt;
using tutorial::SingleString;

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

void doSomething(int argc, char** argv) {

    int n1 = atoi(argv[1]);
    int n2 = atoi(argv[2]);

    ClientContext context1;
    SingleInt divisor;
    SingleString checkDivisor;
    divisor.set_v(n2);
    Status status1 = stub_->check(&context1, divisor, &checkDivisor);
    if (! status1.ok()) { 
        std::cout << "doSomething rpc failed." << std::endl;
        return;
    }
    if (checkDivisor.s() != "OK") {
        std::cout << "Check failed." << std::endl;
        return;
    }

    ClientContext context2;
    IntPair input;
    SingleInt result;
    input.set_a(n1);
    input.set_b(n2);
    Status status2 = stub_->div(&context2, input, &result);
    if (status2.ok()) { 
        std::cout << result.v() << std::endl;
    } else {
        std::cout << "doSomething rpc failed." << std::endl;
    }
}

Step 6

To build the service:

./build.sh

At this point you should have server and client in bin/

Step 7

To test our server locally (without using the blockchain)

./bin/server &
./bin/client 12 4

You should have something like the following output:

./bin/server &

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

./bin/client 12 4

# 3

At this point you have successfully built a gRPC C++ service. The executables in bin/ can be used from anywhere inside the container (they don’t need anything from the installation directory) or outside the container if you have C++ 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 snet

Optionally you can un-publish the service

snet service delete snet 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 snet math-operations