“A toddler standing at the bottom of a tall staircase” by on Mikito Tateisi Unsplash In this post, we are going to take a step by step look at how to test , deploy and interact with a simple Ethereum smart contract using the Go programming language. There are a number of tutorials on the web detailing with how to deploy and interact with Ethereum smart contracts. However, these tutorials are either exclusively done in Javascript or some combination of Javascript and Go. As a budding Gopher and Ethereum enthusiast, I wanted to build, test, deploy and interact with smart contracts on Ethereum using Go. However, I was not able to find a simple step by step guide to help me get started. I had to collect information from disparate sources and dig through the Go Ethereum source code to understand and put together all the required pieces of the puzzle. In this post, I will attempt to use what I have learned to put together an easy to follow step by step guide in the hopes of helping others get productive with Go and Ethereum quickly. This post will be most useful to you if: You are familiar with the Go programming language and have a Go workspace already setup. You have general understanding of the Ethereum Blockchain and the associated Smart Contracts. You have had some exposure to the Solidity programming language used to write Smart Contracts. If you are a complete novice in the Blockchain and Ethereum arena, I would recommend that you get started by: Watching this great for a high level overview of what a Blockchain is. video Working through (literally pull up your favorite text editor and follow along in your favorite programing language) this excellent post on building a block chain. blog Reading the Ethereum . white paper Installing Go-Ethereum and Associated Developer Tools First off, we need to install the Go bindings for the Ethereum protocol. Assuming you have Go installed and have environment variable set appropriately, you can get bindings via: GOPATH $ go get -d github.com/ethereum/go-ethereum Once we have the source code checked out, then we can go ahead and build (Geth is the main command line tool for running a full Go based implementation of an Ethereum node) along with all the developer tools: geth $ cd $GOPATH/src/ $ go install ./... github.com/ethereum Setup Project Structure We will write and deploy a simple Inbox contract. To do so, lets begin by setting up the following directory and file structure: # Navigate to your Go src directory. Mine looks like:# $GOPATH/src/ github.com/sabbas $ cd $GOPATH/src/ github.com/sabbas   $ mkdir -p inbox/contracts   $ touch contracts/inbox_test.go fetch.go update.go deploy.go $ We create a new project folder called . Within this folder, we create a package folder called This folder will contain the Solidity code for our inbox contract along with its associated Go bindings (which we will be generating soon). Within the package folder, we also have an file. This file will contain all our tests. There are three additional files named We will use these additional files to write code to deploy and interact with an Ethereum contract on a public network. These files can be empty for now. inbox contracts. contracts inbox_test.go deploy.go, fetch.go and update.go. Creating a Simple Ethereum Contract We are now ready to write some Solidity code for our Inbox contract. Navigate to the folder and create a file with the name . inbox/contracts Inbox.sol $ tree inbox/inbox/└── contracts└── Inbox.sol Edit the file and add the following lines of Solidity code for our Inbox contract: inbox.sol pragma solidity ^0.4.17; contract Inbox { string public message;  

function Inbox(string initialMessage) public {  
    message = initialMessage;  
}  

function setMessage(string newMessage) public {  
    message = newMessage;  
} } The Inbox contract is pretty straight forward. It has one public data variable called which holds the contents of the most recent message string. The contract also defines a public method which updates the contents of the data variable. message setMessage message Using the Ethereum Contract from Go Now that we our Inbox contract defined in Solidity, we would like to able to use this contract from within our Go application. To be more specific, we would like to have the ability to deploy this contract onto an Ethereum network and interact with it conveniently from within our Go application. Go-Ethereum makes this pretty simple by providing a code generator tool which can transform a Solidity contract file into a type-safe go package which we can import and use directly from within our Go application. This tool is called and it was built and installed during our go-ethereum setup above. To use navigate to the folder and execute: abigen abigen, inbox/contracts $ abigen -sol inbox.sol -pkg contracts -out inbox.go $ tree inboxinbox└── contracts├── Inbox.sol└── inbox.go We pass the name of the Solidity contract file we want to generate the Go package for to the command line argument. We also specify the Go package name and the output file name to the and command line arguments. Running produces the package file containing the Go bindings for the Inbox Solidity contract. Once we have these bindings, we are ready to begin testing the Inbox contract. sol pkg out abigen inbox.go Testing the Ethereum Contract before Deploying to a Public Network Before we deploy our contract to a public Ethereum network, we want to ensure that it is working as expected. In the case of the Inbox contract, we want to test that we can deploy the contract with an initial message, retrieve this initial message and update its value later on. Go-Ethereum provides a nice utility for a blockchain simulator which is extremely helpful with automated unit testing. In the code snippets that follow, we will see how to use the blockchain simulator utility to test the Inbox contract. The method starts off by invoking to generate a private key. This key is used to create a transaction signer function used for authorizing transactions in the simulated blockchain. The transaction signer function along with an address which we can use to make transactions from is generated via a call to This address is then used to create a genesis block containing a single account with some initial balance (via calls to and ). This genesis block is then used to seed the simulated blockchain. Finally, we the next block by explicitly committing all pending transactions and checking if the Inbox contract was deployed at a valid address. TestDeployInbox crypto.GenerateKey bind.NewKeyedTransactor. make(core.GenesisAlloc core.GenesisAccount “mine” We can navigate to and execute to ensure that our deployment test passes inbox\contracts go test $ go test -v=== RUN   TestDeployInbox--- PASS: TestDeployInbox (0.01s)PASSok   github.com/sabbas/inbox/contracts 0.042s Next, we want to test that when we deploy the Inbox contract, it gets deployed with the correct initial message. Similar to the function, the function kicks off by setting up our simulated blockchain (the simulated block chain function can be refactored out into a separate re-usable function. I have avoided that here just to help with readability a bit). It then invokes the function created as part of the auto generated Go bindings for our Inbox Solidity contract. Note that the function returns a pointer to the instance of the deployed Inbox contract as the third return value. We can use this pointer to interact with our deployed Inbox contract(super cool!). And this is exactly what the test does to query and check the initial message stored in the instance of the inbox contract we just deployed. TestDeployInbox TestGetMessage DeployInbox DeployInbox We can navigate to and execute to ensure that our tests pass inbox\contracts go test $ go test -v=== RUN   TestDeployInbox--- PASS: TestDeployInbox (0.01s)=== RUN   TestGetMessage--- PASS: TestGetMessage (0.00s)PASSok   github.com/sabbas/inbox/contracts 0.045s Finally, we want to test that we can update the message data property in the deployed Inbox contract to a new value. The function begins with the same boiler plate code we saw earlier to setup a simulated blockchain and deploy the Inbox contract. As we saw before , a successful invocation of the function call returns a pointer to the instance of the deployed Inbox contract as the third return value. In the function, we use this contract pointer to update the message data property of the Inbox contract by calling the function. Since the function the Inbox contract, it actually generates a new As a result, we pass in a pointer to a struct populated with the transaction authorization data. Since we dont need to send any funds along with the invocation, we set the property of the struct to TestSetMessage DeployInbox TestSetMessage SetMessage SetMessage modifies transaction. TrasactOpts SetMessage Value TransactOpts nil. We can navigate to and run one more time to ensure all is good. inbox\contracts go test $ go test -v=== RUN   TestDeployInbox--- PASS: TestDeployInbox (0.01s)=== RUN   TestGetMessage--- PASS: TestGetMessage (0.00s)=== RUN   TestSetMessage--- PASS: TestSetMessage (0.01s)PASSok   github.com/sabbas/inbox/contracts 0.051s Once our local tests are passing, our Inbox contract is ready for prime time. In the next section we will take a look at how we can take our Inbox contract and deploy it on a public Ethereum network. We will be deploying the Inbox contract on the Ethereum public network. Deploying and interacting with Ethereum contracts on the Ethereum network costs actual money and not necessary when we are just learning or playing around. Rinkeby Test Main To deploy and interact with an Ethereum contract on a public network such as , a couple of things need to be in place: Rinkeby We need to have an account with some funds (ether) on the network We need to be able to connect to and interact with an Ethereum Node. In the sections that follow, we will look at each of these in turn. Creating an Account using Metamask We can create and manage accounts directly from the cli we built earlier. However, when starting out, I found it much simpler to use the in browser Chrome extension. It is quite simple to install Metamask and create an account. I will leave this as an exercise for the reader. geth Metamask Once we are up and running with Metamask and have an account created, we want to make sure that we point Metamask to the Test network Rinkeby Funding the Account The network has a test faucet ( ) running which we can use to request Ether. However, to request ether from this test faucet, we first need to make a post containing just our Ethereum account address(this is account we want to transfer funds into. We can copy this address by clicking on the ellipses right next to the account name on the Metamask extension) on a social networking site and provide a link to the post to the faucet. It’s pretty straight forward. Rinkeby https://faucet.rinkeby.io/ It will take a few seconds and we should see the funds show up in our account in the Metamask extension. Connecting to an Ethereum Node We can use to spin up and manage our own Ethereum node on the Rinkeby test network. This is both resource and time intensive and not always a smooth process. A better alternative is to connect to a running Ethereum node hosted by a third party provider. One such provider is . We can sign-up for a free account with Infura. Once we sign-up, Infura will send us URLS to connect to nodes running on different Ethereum networks. The URL for the Rinkeby test network should look something like . geth Infura https://rinkeby.infura.io/fYE8qC0WiMx4ZAX4Voff Generating Encrypted JSON key for Our Account In order to deploy and interact contracts on a public Ethereum network such as Rinkeby via Go-Ethereum, we need an encrypted json key for the account we created through Metamask above. This is the account we want to be charged for deploying and interacting with the Inbox contract. We can generate this JSON key by exporting the private key (click on the ellipses right next to the account name in metamask to get to the export private key option) for our account in Metamask to a file and then importing it via geth. Make sure you delete the private key file after you have done the import. geth account import path/to/private/key/file The above command will generate an encrypted JSON key file in on a Mac and Take note of this file. We will use its contents in the next section as we deploy and interact with the Inbox contract on the Rinkeby test network. ~/Library/Ethereum/keystore ~/.ethereum. The Final Frontier We have finally made it to the point where we are ready to deploy the Inbox contract to the Rinkeby network. Lets first look at the code that goes into the file we created earlier and then we will walk through it it detail. deploy.go We use the method with Infura url we generated earlier to connect to an Ethereum node on the Rinkeby test network. We then use the utility method to create an authorized transactor from the contents of the key file (you can use command to retrieve the location of your JSON key file on your system) and its associated password we generated above via . From there on, the code to deploy the contract is exactly the same as we have seen when deploying the Inbox contract using the simulated blockchain. Finally, if all goes well, we print the the address at which the Inbox contract is deployed on the network. ethclient.Dial bind.NewTransactor geth account list geth account import $ go run deploy.goContract pending deploy: 0x491c7fd67ac1f0afeceae79447cd98d2a0e6a9ff It will take a few minutes for this contract to be mined and be part of the blockchain. We can check the status via etherscan by navigating to: https://rinkeby.etherscan.io/address/[contract address]. In my case this would be https://rinkeby.etherscan.io/address/0x491c7fd67ac1f0afeceae79447cd98d2a0e6a9ff We can use the address of the deployed Inbox contract to begin interacting with it once it has been mined and included in the blockchain. For example, we can put the code below in the we created above to retrieve the initial message. fetch.go As seen before, we use the method with Infura url we generated earlier to connect to an Ethereum node on the Rinkeby test network. We then use the method generated as part of the Go bindings for the Solidity contract to attach an instance of the Inbox contract to an Inbox contract deployed at a specific address. Finally we access the property on the contract which should print ethclient.Dial NewInbox Message Hello World. $ go run interact.goHello World <nil> We can also update the property on the deployed Inbox contract. To do so, place the code below in the file created earlier. Message update.go Recall that the function the Inbox contract and actually generates a new As a result, we pass in a pointer to a struct populated with the transaction authorization data. Again, It will take a few minutes for this transaction to be mined and be part of the blockchain. Once it is mined and included in the blockchain, we can follow the earlier example of retrieving the property from the deployed contract to see the updated value. SetMessage modifies transaction. TrasactOpts Message There is a lot we can do with Go Ethereum but just getting started could be a bit over whelming. Hopefully this post has given you a starting point from where you could explore further.

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