Scala hyperledger fabric client with akka actors

Akka + Hlf - A marriage made in heaven

(λx.x)eranga

Published in

Coinmonks

4 min readJan 17, 2019

Happyledger :)

This is the second part of my hyperledger fabric blog series - Happyledger blog series :). In this post I’m gonna cover how to write scala based hyperldger fabric client application. Most of the hyperledger fabric client applications writs with node sdk. It’s worth to try it with jvm based language as well. So I have written scala based client to interact with fabric network. Full source code of my application available at gitlab repository in here. Please clone it and follow the steps below.

1. Start fabric network

In my pervious post I have shown how to setup hyperledger fabric network with multiple orderers and kafka. In this post I’m gonna use it to setup the network. If you follow the previous post and up the network you will ended up with following running services

One ca container
Three orderer containers
Three peer containers
Three zookeeper containers
Four kafka containers
One cli container

2. Add fabric dependency

In order to scala client to interact with hlf network build.sbt need to have hyperledger-fabric-java-sdk dependency. Following is the build.sbt file dependencies(it has some other dependencies as well).

3. Implement fabric user

In order to interact with hlf network our client need to have fabric users(admin and normal users). So in our application we need to define a user with implementing org.hyperledger.fabric.sdk.User interface. So I have created a PeezUser with a case class.

Now we can create instances of this user and interact with the hlf network peers.

4. Create CA client

All the users in hlf network need to have their own certificate materials. Since we have ca service running we can use it to generate crypto materials for our users. That is the advantage of having ca service. All the user crypto materials can be generated via communicating with ca service.

In order to interact with ca service we need to have a ca client. Fabric java-sdk provide HFCAClient which we can use instantiate a ca client in our scala application. This function takes the ca service uri as an argument. In our case we are running ca service on 7054 port on local machine.

5. Enroll users

Now our ca client is created, so we can enroll users to the network by generating crypto materials.

There are two types of users in hlf, admin and normal user. In here I have two functions to enroll the different user types. enrollAdmin enrolls the admin users. When enrolling admin users, it user admin user credentials which defines in docker-compose ca service command section. Function enrollUser enrolls normal users(note that to enroll normal users we need to have admin user).

When enrolling a user, ca client returns the enrollment object which contains private key and the certificate of the user. In here I’m using java object serialization to save that enrollment object in local file system. So when enrolling a user it first checks weather the given user already enrolled by UserStore.get(userId) function. If user already enrolled we take enrolled user(UserStore manages saving and loading users from file system).

6. Create fabric client

Next thing is to create hyperledger fabric client which comes in HFClient. This client do all the transaction executions, channel discoveries etc with the hlf network.

7. Connect to channel

Now we can connect to channel by using previously created client. When connecting to channel, we need to define the peer, orderer and channel name. All the peers and orders in hlf exposes GRPC endpoints (peers and orders have their own GRPC endpoints to talk). We need to define GRPC end points of peer and orderer like below and connect to the channel.

8. Execute query transactions

There are two types of transactions which can execute in fabric chaincodes, query and invoke. Following is the function to execute query transaction on mycc chaincode which installed on our fabric network.

There is a builder which comes with ChaincodeID. We can set chaincode name, function and arguments with this builder and execute the queries.

9. Execute invoke transactions

Following is the function to execute invoke transaction on mycc chaincode which installed on our fabric network.

In here we need to send TransactionProposal to the network initially. Then it will response back the ProposalResponse list. If all the responses are correct, we can send the transaction to the network with sendTransaction.

The sendTransaction function returns CompletableFuture with TransactionEvent. We can handle the future and obtained the TransactionEvent to decide weather the transaction is successful or not( weather transaction included to a block or not).

9. Akka actor to communicate

Finally I have created akka actor to interact with the functions defined in above section. It consumes Init and Exec messages. When Init message comes actor setup the ca client, hlf client and channel. When ExecQuery message comes it execute query transactions to the ledger. For ExecInvoke message it executes invoke transactions to the ledger.

References

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