Saturday, March 30, 2019

Oracle BlockChain Service: creating a smart contract aka how to write a chaincode

In the first blog about blockchain, I used Oracle Compute Cloud Classic and installed MultiChain on it. Since then, Oracle has released a Blockchain Cloud Service with a lot of out of the box functionality, based on Hyperledger.

In this blog post I will describe how to create a smart contract for a webshop use case: getting offers from different suppliers for a specific order. I already know node.js so I will write the ChainCode in node. Note that go is also supported.

Prerequisites

  • A running instance of Oracle Blockchain Service
  • Node.js installed on your laptop
There are a number of steps involved in writing a smart contract (or chaincode).
  1. Design the chaincode
  2. Write a chaincode (in Node)
  3. Deploy a ChainCode to a Peer 
  4. Test the chaincode with Postman

Design 

Before you write a chaincode, you need to know what transactions need to be supported. In our example we have a webshop, that issues requests for shipping after ordering an item. Shippers can create an offer. If they are selected by the customer, they pickup the shipment. The customer receives the goods at the end of the cycle. For more information about designing the chaincode, see the hyperledger documentation


Write a ChainCode

The easiest way to write the chaincode is to download an example from the Oracle BlockChain Service and modify it.

  1. Navigate to the Blockchain console and click on Developers tools.
  2. Click on Download oracle samples
  3. Download the Cardealer sample and unzip it
  4. Navigate to [yourpath]\CarDealer\artifacts\src\github.com\node and copy cardealer_cc
  5. Paste the cardealer_cc in a new folder where you want to store your code and rename it to shipment_cc
  6. Leave the methods Init and Invoke as is and create methods to issue, offer, select, pickup and receive a shipment. 

        ---------------code snippet--------------------------------
        shipment.orderId = args[0];
        shipment.product = args[1].toLowerCase();
        shipment.customer = args[2].toLowerCase();
        shipment.shippingAddress = args[3];
        shipment.orderDate = parseInt(args[4]);
        if (typeof shipment.orderDate !== 'number') {
            throw new Error('5th argument must be a numeric string');
        }
        shipment.custodian = args[5].toLowerCase();
        shipment.currentState = shState.ISSUED;
        shipment.offers = [];

        // ==== Check if shipment already exists ====
        let shipmentAsBytes = await stub.getState(shipment.orderId);
        if (shipmentAsBytes.toString()) {
            console.info('This shipment already exists: ' + shipment.orderId);
            jsonResp.Error = 'This shipment already exists: ' + shipment.orderId;
            throw new Error(JSON.stringify(jsonResp));
        }

        // ==== Create shipment object and marshal to JSON ====
        let shipmentJSONasBytes = Buffer.from(JSON.stringify(shipment));

        // === Save shipment to state ===
        await stub.putState(shipment.orderId, shipmentJSONasBytes);


        -------------end code snippet --------------------------

Deploy the chaincode

After writing the chaincode, it needs to be deployed to the blockchain. In this example we will deploy it to the shipment channel using the quick start. This will instantiate it and use the default endorsement policy. Please note that channels and chaincodes can't be deleted after creating and deploying them.

  1. Zip the code and the package.json in a zip
  2. Click on "Deploy a new Chaincode" in the chaincode menu in the blockchain console.
  3. Click on Quick Deployment
  4. Fill out the right details




  5. Upload the zipfile and wait until the dialog shows that the chaincode is instantiated and deployed succesfully. 
  6. Enable the rest proxy by going to the chaincode and clicking on the hamburger menu. Click on "Enable on REST Proxy". 
  7. Fill out the fields as shown in the figure below

Test the chaincode

Now that we have deployed the chaincode, we can test it using the REST proxy. Before you do this, make sure you have the right role associated with your user (RESTPROXY4_USER)
  1. Open postman
  2. Create a new "Post request" to issue a shipment
  3. Go to the blockchain console and find the URL that is listed for the RESTProxy that you enabled for your chaincode
  4. Create a request that looks as follows: 
curl -X POST \
      https://restserver:port/restproxy4/bcsgw/rest/v1/transaction/asyncInvocation \
        -H 'Authorization: Basic xxx' \
          -H 'Content-Type: application/json' \
            -H 'cache-control: no-cache' \
              -d '{
              "args":[1,"iron","John Doe","Rembrandtlaan 22c Bilthoven","0330","webshop"],
                "channel": "testshipping",
                  "chaincode": "shipment",
                    "chaincodeVer":"1.0",
                      "method": "issueShipment"
                        }'

                        The result should like this:


                        {
                            "returnCode": "Success",
                            "txid": "a4f5e851734f7e3ebdfa0761bfd54bab090cdaf08266363fe2451eacc3a14826"
                        }

                        Next steps

                        You can now query the result of this transaction, read the shipment etc.

                        Happy coding! 😃

                        Monday, January 21, 2019

                        Another blockchain: installing Ethereum on Oracle Cloud

                        After installing MultiChain on Oracle Compute Cloud, and playing around with HyperLedger on the Oracle Blockchain Cloud service, I now ran into a case where Ethereum was used.

                        This blog post describes how I installed a Ethereum node on Oracle Cloud Infrastructure.

                        Prerequisites

                        • An account on Oracle Cloud with Administrator rights
                        • You have generated an ssh key-pair
                        • You are logged in to your cloud account

                        Create Compartment

                        Create a compartment with the name Ethereum to separate this from your other infrastructure. You can find this under "Identity".

                        Create a Virtual Cloud Network

                        1. Navigate to Virtual Cloud Network, by selecting Network from the Menu
                        2. Select the compartment you just created
                        3. Click "Create Virtual Cloud Network"
                        • The compartment will default to the compartment you just selected
                        • Name: ethereum-network
                        • select "Create Virtual Cloud Network plus related resources" to quickly get up and running
                        • Click "Create"
                        A dialog is displayed that shows you what has been created, after a few seconds.

                        Create compute nodes

                        For this example I will create 3 nodes on 3 separate VMs.
                        1. Go to the Compute Menu
                        2. Select "Ethereum" in the compartment dropdown (left side of the menu)
                        3. Click Create Instance
                        4. Give the instance a name (ethereum-node1 for example)
                        5. Leave all the defaults for shape and OS
                        6. Upload your public key
                        7. Select the networking you created (ethereum-network)
                        8. Click "Create"
                        Repeat this process for 2 more nodes (giving them separate names of course).

                        You should have three nodes now, like the picture below shows. It might take a couple of minutes before they are completely done, but not longer than 5 minutes.











                        You can connect to your instance as "opc" using the private key and the public IP address that is published in the console.

                        Install Ethereum

                        To install Ethereum for Oracle Enterprise Linux, you have to install it from source. There is no package available.

                        You need git, go and gcc. The easiest way is to install development tools

                        • sudo /usr/bin/ol_yum_configure.sh
                        • sudo yum update
                        • sudo yum groupinstall 'Development Tools'
                        • sudo yum install gettext-devel openssl-devel perl-CPAN perl-devel zlib-devel
                        • sudo yum install curl-devel

                        Install git

                        • sudo wget https://github.com/git/git/archive/v2.10.1.tar.gz -O git.tar.gz
                        • tar -zxf git.tar.gz
                        • cd git-2.10.1/
                        • make configure
                        • ./configure --prefix=/usr/local
                        • sudo make install
                        • git --version to check the installation

                        Install go

                        • cd ~
                        • wget https://dl.google.com/go/go1.11.4.linux-amd64.tar.gz
                        • sudo tar -C /usr/local -xzf go1.11.4.linux-amd64.tar.gz
                        • add go to your path by editing .bash_profile
                        • go version to check the installation

                        Install geth

                        To create the private network, we need to install geth, the command line tool that runs a ful Ethereum node implemented in Go. It offers three interfaces: 
                        1. the command line subcommands and options
                        2. a Json-rpc server
                        3. An interactive console
                        Execute the following commands
                        • cd ~
                        • git clone https://github.com/ethereum/go-ethereum
                        • cd go-ethereum
                        • make geth
                        • add build/bin to your path by editing your .bash_profile

                        Start the node

                        You can start a node by running build/bin/geth. This will add this node to the public ethereum network. This node is now part of the Ethereum network.


                        If you don't want to be part of the public network, you can also create a private network. https://github.com/ethereum/go-ethereum/wiki/Private-network.


                        Happy coding 😊