Blocky

Ethereum based smart contracts for IoT devices

Quick Links

Install Dependencies
Create Private Ethereum Testnet
Create Smart Contracts

Install Dependencies

Install Go

Download precompiled Go binaries from official project site

For x86_64 Linux

$ curl -O https://storage.googleapis.com/golang/go1.7.4.linux-amd64.tar.gz

For Raspberry Pi Linux

$ curl -O https://storage.googleapis.com/golang/go1.7.4.linux-armv6l.tar.gz

Install Go binaries

$ sudo tar -C /usr/local -xzf go$VERSION.$OS-$ARCH.tar.gz

Add path to /etc/profile (for a system-wide installation) or $HOME/.profile

$ export PATH=$PATH:/usr/local/go/bin

Install Ethereum Client

$ git clone https://github.com/ethereum/go-ethereum.git
$ cd go-ethereum
$ make geth
$ sudo cp build/bin/geth /usr/local/bin/geth

Create Private Ethereum Testnet

Setup Node Zero

Create a new account for private net

$ geth --datadir "~/private-iot-chain" account new

Note account number and pre-allocate ether for the new account in genesis.json (i.e. change account address in "alloc" accordingly)

{
    "nonce": "0x0000000000000042",
    "timestamp": "0x0",
    "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "extraData": "0x0",
    "gasLimit": "0x8000000",
    "difficulty": "0x400",
    "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "coinbase": "0x3333333333333333333333333333333333333333",
    "alloc": {
        "0x80d4dddffd9d1292f16045166aecdaf34b82a0fb": {
            "balance": "20000000000000000000"
        }
    }
}

Create a private chain with the custom genesis block

$ geth --datadir "~/private-iot-chain" init genesis.json

Launch geth for private net

$ geth --rpc --rpcport "8000" --rpccorsdomain "*" --datadir "~/private-iot-chain" --port "30303" --nodiscover --ipcapi "admin,db,eth,debug,miner,net,shh,txpool,personal,web3" --rpcapi "db,eth,net,web3" --autodag --identity "zero" --networkid 666 console

Run eth.getBalance(eth.coinbase) command to check the account balance, pre-allocated sum should be there
Run admin.nodeInfo to get enode url (enode://xxxxx) and add ip address of the interface [::] to construct the complete enode address to share with other peers

"enode://6ad5934db83a0266c4c6d5048d02f86b3e69251d45ad411387cde9cc5a86030f2bee4bcbe200d4238d91b01c94444e562986058c9c4acca2a92cb81eb012acfc@192.168.2.41:30303?discport=0"

Setup Node One

Setup second one which is a second computer on our net

$ geth --datadir "~/private-iot-chain" account new
$ geth --datadir "~/private-iot-chain" init genesis.json
$ geth --datadir "~/private-iot-chain" --port "30303" --nodiscover --identity "one" --networkid 666 console

Run admin.addPeer to connect node zero

> admin.addPeer("enode://6ad5934db83a0266c4c6d5048d02f86b3e69251d45ad411387cde9cc5a86030f2bee4bcbe200d4238d91b01c94444e562986058c9c4acca2a92cb81eb012acfc@192.168.2.41:30303")

Send ether from node zero to one using one's wallet address. Execute on node zero, do not forget mine transaction

> personal.unlockAccount(eth.coinbase)
> eth.sendTransaction({from:eth.coinbase, to: '0xcb2a95f964acf8adee7fae30cf5dc6a3f5e14a5c', value: web3.toWei(.000000000001, "ether")})
> miner.start()
> miner.stop()

Ethereum

• Creating a private chain/testnet
• Setting up an Ethereum testnet
• Setting up private network or local cluster

Create Smart Contracts

Install Solidity Compiler

To develop smart contracts Solidity compiler is needed. Either Solidity online compiler or internal/offline compiler should be used. Console command eth.getCompilers() will list available offline compilers, if solidity is not present, build commands are as follows:

$ git clone --recursive https://github.com/ethereum/solidity.git
$ cd solidity
$ git checkout tags/<tag_name>
$ ./scripts/install_deps.sh
$ mkdir build
$ cd build
$ cmake .. && make

Create and Deploy Smart Contracts

Below is a sample smart contract which get/set a variable.

pragma solidity ^0.4.0;

contract store {
    uint data;

    function set(uint x) {
        data = x;
    }

    function get() constant returns (uint) {
        return data;
    }
}

For ease of use Solidity online compiler will be used. Copy the sample contract into code window and it will generate corresponding web3 code (right panel) which should be copied into store.js file

var storeContract = web3.eth.contract([{"constant":false,"inputs":[{"name":"x","type":"uint256"}],"name":"set","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"get","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"}]);
var store = storeContract.new(
   {
     from: web3.eth.accounts[0], 
     data: '0x606060405234610000575b6090806100176000396000f360606040526000357c01000000000000000000000000000000000000000000000000000000009004806360fe47b11460405780636d4ce63c14605a575b6000565b3460005760586004808035906020019091905050607a565b005b3460005760646085565b6040518082815260200191505060405180910390f35b806000819055505b50565b600060005490505b9056', 
     gas: '4700000'
   }, function (e, contract){
    console.log(e, contract);
    if (typeof contract.address !== 'undefined') {
         console.log('Contract mined! address: ' + contract.address + ' transactionHash: ' + contract.transactionHash);
    }
 })

Copied store.js file can be loaded via console (do not forget to personal.unlockAccount())

> loadScript('store.js');
I1211 14:28:58.352087 internal/ethapi/api.go:1045] Tx(0x6a774d17b83dfaf96b1a233107f8b2fa43f7411a71e87d273403b8a9e7efe254) created: 0x366e0869aea00583c5a5ff62309214707d82e60c
null [object Object]
true

Contract is loaded however it should be mined to get deployed.

> miner.start()
true
> I1211 14:29:25.804431 miner/miner.go:137] Starting mining operation (CPU=2 TOT=3)
I1211 14:29:25.808925 miner/worker.go:563] commit new work on block 271 with 1 txs & 0 uncles. Took 4.445739ms
I1211 14:29:26.362327 miner/worker.go:362] 🔨  Mined block (#271 / 1fb173c0). Wait 5 blocks for confirmation
I1211 14:29:26.362897 miner/worker.go:563] commit new work on block 272 with 0 txs & 0 uncles. Took 264.496µs
I1211 14:29:26.363044 miner/worker.go:458] 🔨 🔗  Mined 5 blocks back: block #266
null [object Object]
Contract mined! address: 0x366e0869aea00583c5a5ff62309214707d82e60c transactionHash: 0x6a774d17b83dfaf96b1a233107f8b2fa43f7411a71e87d273403b8a9e7efe254
I1211 14:29:28.336365 miner/worker.go:362] 🔨  Mined block (#272 / f58ea260). Wait 5 blocks for confirmation
I1211 14:29:28.336902 miner/worker.go:563] commit new work on block 273 with 0 txs & 0 uncles. Took 229.156µs
I1211 14:29:28.337054 miner/worker.go:458] 🔨 🔗  Mined 5 blocks back: block #267

> miner.stop()
true

Now contract is ready to be used

> store
{
  abi: [{
      constant: false,
      inputs: [{...}],
      name: "set",
      outputs: [],
      payable: false,
      type: "function"
  }, {
      constant: true,
      inputs: [],
      name: "get",
      outputs: [{...}],
      payable: false,
      type: "function"
  }],
  address: "0x366e0869aea00583c5a5ff62309214707d82e60c",
  transactionHash: "0x6a774d17b83dfaf96b1a233107f8b2fa43f7411a71e87d273403b8a9e7efe254",
  allEvents: function(),
  get: function(),
  set: function()
}

Use store.get() and store.set() to print and modify stored data

> store.get()
0
> personal.unlockAccount(eth.coinbase, YOUR_PASSWORD)

true
> store.set(42,{from: eth.coinbase, gas: 3000000})
I1211 14:58:32.122266 internal/ethapi/api.go:1047] Tx(0x18287c995d686f9fa2bee9136e4b0d92d0d5d0121145eaeba849fd6218a923f0) to: 0x366e0869aea00583c5a5ff62309214707d82e60c
"0x18287c995d686f9fa2bee9136e4b0d92d0d5d0121145eaeba849fd6218a923f0"
> 
> store.get()
0
> miner.start()
true
> I1211 14:58:42.441663 miner/miner.go:137] Starting mining operation (CPU=2 TOT=3)
I1211 14:58:42.446231 miner/worker.go:563] commit new work on block 273 with 1 txs & 0 uncles. Took 4.515457ms
I1211 14:58:42.723401 miner/worker.go:362] 🔨  Mined block (#273 / 54a33c4b). Wait 5 blocks for confirmation
....
> miner.stop()
true
> store.get()
42

In order to access contract from another node (node one) and modify data, contract ABI and ADDRESS should be known. This info can be acquired via commands below on node zero.

> store.abi
[{
    constant: false,
    inputs: [{
        name: "x",
        type: "uint256"
    }],
    name: "set",
    outputs: [],
    payable: false,
    type: "function"
}, {
    constant: true,
    inputs: [],
    name: "get",
    outputs: [{
        name: "",
        type: "uint256"
    }],
    payable: false,
    type: "function"
}]
> store.address
"0x366e0869aea00583c5a5ff62309214707d82e60c"

Following command template should be executed on node one:

> var store_on_blockchain = eth.contract(CONTRACT_ABI).at(CONTRACT_ADDRESS);

Paragraph and line breaks should be removed from CONTRACT_ABI, this site can be used to do it

> var store_on_blockchain = eth.contract([{ constant: false, inputs: [{ name: "x", type: "uint256" }], name: "set", outputs: [], payable: false, type: "function" }, { constant: true, inputs: [], name: "get", outputs: [{ name: "", type: "uint256" }], payable: false, type: "function" }]).at("0x366e0869aea00583c5a5ff62309214707d82e60c");

From now on node one can interact with the deployed "store" contract

> personal.unlockAccount(eth.coinbase, YOUR_PASSWORD)
true
> store_on_blockchain.set(1234,{from: eth.coinbase, gas: 3000000})
I1211 17:39:00.704042 internal/ethapi/api.go:1047] Tx(0x30b562bad71cf67ea4cbf24ad5c7ec8891f6c2ed5f0c9813f3d65be6f05009a2) to: 0x366e0869aea00583c5a5ff62309214707d82e60c
"0x30b562bad71cf67ea4cbf24ad5c7ec8891f6c2ed5f0c9813f3d65be6f05009a2"
> store_on_blockchain.get()
1234

Smart Contracts

• Introduction to Smart Contracts
• Smart Contract Events