Native DApps: Go bindings to Ethereum contracts

The original roadmap and/or dream of the Ethereum platform was to provide a solid, high performing client implementation of the consensus protocol in various languages, which would provide an RPC interface for JavaScript DApps to communicate with, pushing towards the direction of the Mist browser, through which users can interact with the blockchain.

Although this was a solid plan for mainstream adoption and does cover quite a lot of use cases that people come up with (mostly where people manually interact with the blockchain), it eludes the server side (backend, fully automated, devops) use cases where JavaScript is usually not the language of choice given its dynamic nature.

This page introduces the concept of server side native Dapps: Go language bindings to any Ethereum contract that is compile time type safe, highly performant and best of all, can be generated fully automatically from a contract ABI and optionally the EVM bytecode.

This page is written in a more beginner friendly tutorial style to make it easier for people to start out with writing Go native Dapps. The used concepts will be introduced gradually as a developer would need/encounter them. However, we do assume the reader is familiar with Ethereum in general, has a fair understanding of Solidity and can code Go.

Token contract

To avoid falling into the fallacy of useless academic examples, we're going to take the official Token contract as the base for introducing the Go native bindings. If you're unfamiliar with the contract, skimming the linked page should probably be enough, the details aren't relevant for now. In short the contract implements a custom token that can be deployed on top of Ethereum. To make sure this tutorial doesn't go stale if the linked website changes, the Solidity source code of the Token contract is also available at token.sol.

Go binding generator

Interacting with a contract on the Ethereum blockchain from Go (or any other language for a matter of fact) is already possible via the RPC interfaces exposed by Ethereum clients. However, writing the boilerplate code that translates decent Go language constructs into RPC calls and back is extremely time consuming and also extremely brittle: implementation bugs can only be detected during runtime and it's almost impossible to evolve a contract as even a tiny change in Solidity can be painful to port over to Go.

To avoid all this mess, the go-ethereum implementation introduces a source code generator that can convert Ethereum ABI definitions into easy to use, type-safe Go packages. Assuming you have a valid Go development environment set up, godep installed and the go-ethereum repository checked out correctly, you can build the generator with:

$ cd $GOPATH/src/github.com/go-ethereum
$ godep go install ./cmd/abigen

Generating Go bindings

The single essential thing needed to generate a Go binding to an Ethereum contract is the contract's ABI definition JSON file. For our Token contract tutorial you can obtain this either by compiling the Solidity code yourself (e.g. via @chriseth's online Solidity compiler), or you can download our pre-compiled token.abi.

To generate a binding, simply call:

$ abigen --abi token.abi --pkg main --type Token --out token.go

Where the flags are:

• --abi: Mandatory path to the contract ABI to bind to
• --pgk: Mandatory Go package name to place the Go code into
• --type: Optional Go type name to assign to the binding struct
• --out: Optional output path for the generated Go source file (not set = stdout)

This will generate a type-safe Go binding for the Token contract. The generated code will look something like token.go, but please generate your own as this will change as more work is put into the generator.

Accessing an Ethereum contract

To interact with a contract deployed on the blockchain, you'll need to know the address of the contract itself, and need to specify a backend through which to access Ethereum. The binding generator provides out of the box an RPC backend through which you can attach to an existing Ethereum node via IPC, HTTP or WebSockets.

We'll use the foundation's Unicorn token contract deployed on the testnet to demonstrate calling contract methods. It is deployed at the address 0x21e6fc92f93c8a1bb41e2be64b4e1f88a54d3576.

package main

import (
	"fmt"
	"log"

	"github.com/ethereum/go-ethereum/accounts/abi/bind/backends"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/rpc"
)

func main() {
	// Create an IPC based RPC connection to a remote node
	conn, err := rpc.NewIPCClient("/home/karalabe/.ethereum/testnet/geth.ipc")
	if err != nil {
		log.Fatalf("Failed to connect to the Ethereum client: %v", err)
	}
	// Instantiate the contract and ready its name
	token, err := NewToken(common.HexToAddress("0x21e6fc92f93c8a1bb41e2be64b4e1f88a54d3576"), backends.NewRPCBackend(conn))
	if err != nil {
		log.Fatalf("Failed to instantiate a Token contract: %v", err)
	}
	name, err := token.Name(nil)
	if err != nil {
		log.Fatalf("Failed to retrieve token name: %v", err)
	}
	fmt.Println("Token name:", name)
}

And the output (yay):

Token name: Testnet Unicorn

If you look at the method invoked to read the token name token.Name(nil), it required a parameter to be passed, even though the original Solidity contract requires none. This is a *bind.CallOpts type, which can be used to fine tune the call. Most importantly, it can be used to specify whether to run the call against the current final state of the contract on the blockchain (default), or to also include any pending modifications (&bind.CallOpts(Pending: true)).

Transacting with an Ethereum contract

Authorized sessions

Deploying new instances of a contract