Example of starting a contract¶

Hint

Technical description of contracts implementation is given in module Docker Smart Contracts.

Description of program logic¶

This module reviews an example of how to create and run a simple smart contract. The contract performs increment the number transferred to the contract entry in call-transactions.

Program listing contract.py on Python:

import json
import os
import requests
import sys


def find_param_value(params, name):
    for param in params:
        if param['key'] == name: return param['value']
    return None


def print_success(results):
    print(json.dumps(results, separators=(',', ':')))


def print_error(message):
    print(message)
    sys.exit(3)


def get_value(contract_id):
    node = os.environ['NODE_API']
    if not node:
        print_error("Node REST API address is not defined")
    token = os.environ["API_TOKEN"]
    if not token:
        print_error("Node API token is not defined")
    headers = {'X-Contract-Api-Token': token}
    url = '{0}/internal/contracts/{1}/sum'.format(node, contract_id)
    r = requests.get(url, verify=False, timeout=2, headers=headers)
    data = r.json()
    return data['value']


if __name__ == '__main__':
    command = os.environ['COMMAND']
    if command == 'CALL':
        contract_id = json.loads(os.environ['TX'])['contractId']
        value = get_value(contract_id)
        print_success([{
            "key": "sum",
            "type": "integer",
            "value": value + 1}])
    elif command == 'CREATE':
        print_success([{
            "key": "sum",
            "type": "integer",
            "value": 0}])
    else:
        print_error("Unknown command {0}".format(command))

Description of operation

The program expects to get the data structure in json format with the field “params”.
It reads the values of the “a” fields.
Returns the result as a value of field “{a} + 1” in json format.

Example of incoming parameters

"params":[
    {
        "key":"a",
        "type":"integer",
        "value":1
    }
]

Installing a smart contract¶

Download and install Docker for Developers for your operating system.
Prepare a contract image. In the stateful-increment-contract folder, create the following files:

contract.py
Dockerfile
run.sh

Listing of run.sh file

#!/bin/sh

python contract.py

Dockerfile File Listing

FROM python:alpine3.8
ADD contract.py /
ADD run.sh /
RUN chmod +x run.sh
RUN apk add --no-cache --update iptables
CMD exec /bin/sh -c "trap : TERM INT; (while true; do sleep 1000; done) & wait"

Important

It is required to install iptables into the smart contract container.

Install the image in Docker registry. Execute the following commands in the terminal:

docker run -d -p 5000:5000 --name registry registry:2
cd contracts/stateful-increment-contract
docker build -t stateful-increment-contract .
docker image tag stateful-increment-contract localhost:5000/stateful-increment-contract
docker start registry
docker push localhost:5000/stateful-increment-contract

Run the following command in the terminal to get the information about the container:

docker inspect 57c2c2d2643d
[
{
    "Id": "sha256:57c2c2d2643da042ef8dd80010632ffdd11e3d2e3f85c20c31dce838073614dd",
    "RepoTags": [
        "wenode:latest"
    ],
    "RepoDigests": [],
    "Parent": "sha256:d91d2307057bf3bb5bd9d364f16cd3d7eda3b58edf2686e1944bcc7133f07913",
    "Comment": "",
    "Created": "2019-10-25T14:15:03.856072509Z",
    "Container": "",
    "ContainerConfig": {
        "Hostname": "",
        "Domainname": "",
        "User": "",
        "AttachStdin": false,
        "AttachStdout": false,
        "AttachStderr": false,

The smart contract identifier Id is the value of the imageHash field and it is used in transactions with the created smart contract.

Sign a transaction to create a smart contract. In this example, the transaction is signed with the key stored in the node keystore.

Hint

To create a key pair and the participant address, use the utility generators.jar. The procedure for creating a key pair is given in item 1 of the module “Connecting to the Network”. The rules for generating queries to the node are given in the module Node REST API.

Query Body

{
  "fee": 100000000,
  "image": "stateful-increment-contract:latest",
  "imageHash": "7d3b915c82930dd79591aab040657338f64e5d8b842abe2d73d5c8f828584b65",
  "contractName": "stateful-increment-contract",
  "sender": "3PudkbvjV1nPj1TkuuRahh4sGdgfr4YAUV2",
  "password": "",
  "params": [],
  "type": 103,
  "version": 1
 }

Sample query

curl -X POST --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'X-Contract-Api-Token' -d '    { \
        "fee": 100000000, \
        "image": "stateful-increment-contract:latest", \
        "imageHash": "7d3b915c82930dd79591aab040657338f64e5d8b842abe2d73d5c8f828584b65", \
        "contractName": "stateful-increment-contract", \
        "sender": "3PudkbvjV1nPj1TkuuRahh4sGdgfr4YAUV2", \
        "password": "", \
        "params": [], \
        "type": 103, \
        "version": 1 \
    }' 'http://localhost:6862/transactions/sign'

Sample response

{
    "type": 103,
    "id": "ULcq9R7PvUB2yPMrmBdxoTi3bcRmQPT3JDLLLZVj4Ky",
    "sender": "3N3YTj1tNwn8XUJ8ptGKbPuEFNa9GFnhqew",
    "senderPublicKey": "3kW7vy6nPC59BXM67n5N56rhhAv38Dws5skqDsjMVT2M",
    "fee": 500000,
    "timestamp": 1550591678479,
    "proofs": [ "yecRFZm9iBLyDy93bDVaNo1PR5Qkkic7196GAgUt9TNH1cnQphq4yGQQ8Fxj4BYA4TaqYVw5qxtWzGMPQyVeKYv" ],
    "version": 1,
    "image": "stateful-increment-contract:latest",
    "imageHash": "7d3b915c82930dd79591aab040657338f64e5d8b842abe2d73d5c8f828584b65",
    "contractName": "stateful-increment-contract",
    "params": [],
    "height": 1619
}

Send the signed transaction to the blockchain. The response from the sign method must be transferred to the input for the broadcast method.

Sample query

curl -X POST --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'X-Contract-Api-Token' -d '{ \
{
    "type": 103, \
    "id": "ULcq9R7PvUB2yPMrmBdxoTi3bcRmQPT3JDLLLZVj4Ky", \
    "sender": "3N3YTj1tNwn8XUJ8ptGKbPuEFNa9GFnhqew", \
    "senderPublicKey": "3kW7vy6nPC59BXM67n5N56rhhAv38Dws5skqDsjMVT2M", \
    "fee": 500000, \
    "timestamp": 1550591678479, \
    "proofs": [ "yecRFZm9iBLyDy93bDVaNo1PR5Qkkic7196GAgUt9TNH1cnQphq4yGQQ8Fxj4BYA4TaqYVw5qxtWzGMPQyVeKYv" ], \
    "version": 1, \
    "image": "stateful-increment-contract:latest", \
    "imageHash": "7d3b915c82930dd79591aab040657338f64e5d8b842abe2d73d5c8f828584b65", \
    "contractName": "stateful-increment-contract", \
    "params": [], \
    "height": 1619 \
}
}' 'http://localhost:6862/transactions/broadcast'

Use the transaction ID to check that the contract initiation transaction is placed in the blockchain.

Sample response

{
    "type": 103,
    "id": "ULcq9R7PvUB2yPMrmBdxoTi3bcRmQPT3JDLLLZVj4Ky",
    "sender": "3N3YTj1tNwn8XUJ8ptGKbPuEFNa9GFnhqew",
    "senderPublicKey": "3kW7vy6nPC59BXM67n5N56rhhAv38Dws5skqDsjMVT2M",
    "fee": 500000,
    "timestamp": 1550591678479,
    "proofs": [ "yecRFZm9iBLyDy93bDVaNo1PR5Qkkic7196GAgUt9TNH1cnQphq4yGQQ8Fxj4BYA4TaqYVw5qxtWzGMPQyVeKYv" ],
    "version": 1,
    "image": "stateful-increment-contract:latest",
    "imageHash": "7d3b915c82930dd79591aab040657338f64e5d8b842abe2d73d5c8f828584b65",
    "contractName": "stateful-increment-contract",
    "params": [],
    "height": 1619
}

Smart Contract Execution¶

Sign a call-transaction to call (execute) the smart contract.

In the ‘’contractID’’ field, specify the contract initialization transaction ID.

Query Body

{
    "contractId": "2sqPS2VAKmK77FoNakw1VtDTCbDSa7nqh5wTXvJeYGo2",
    "fee": 10,
    "sender": "3PKyW5FSn4fmdrLcUnDMRHVyoDBxybRgP58",
    "password": "",
    "type": 104,
    "version": 1,
    "params": [
        {
            "type": "integer",
            "key": "a",
            "value": 1
        }
    ]
}

Sample query

curl -X POST --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'X-Contract-Api-Token' -d '{ \
    "contractId": "2sqPS2VAKmK77FoNakw1VtDTCbDSa7nqh5wTXvJeYGo2", \
    "fee": 10, \
    "sender": "3PKyW5FSn4fmdrLcUnDMRHVyoDBxybRgP58", \
    "password": "", \
    "type": 104, \
    "version": 1, \
    "params": [ \
        { \
            "type": "integer", \
            "key": "a", \
            "value": 1 \
        } \
    ] \
}' 'http://localhost:6862/transactions/sign'

Sample response

{
    "type": 104,
    "id": "9fBrL2n5TN473g1gNfoZqaAqAsAJCuHRHYxZpLexL3VP",
    "sender": "3PKyW5FSn4fmdrLcUnDMRHVyoDBxybRgP58",
    "senderPublicKey": "2YvzcVLrqLCqouVrFZynjfotEuPNV9GrdauNpgdWXLsq",
    "fee": 10,
    "timestamp": 1549365736923,
    "proofs": [
        "2q4cTBhDkEDkFxr7iYaHPAv1dzaKo5rDaTxPF5VHryyYTXxTPvN9Wb3YrsDYixKiUPXBnAyXzEcnKPFRCW9xVp4v"
    ],
    "version": 1,
    "contractId": "2sqPS2VAKmK77FoNakw1VtDTCbDSa7nqh5wTXvJeYGo2",
    "params": [
        {
        "key": "a",
        "type": "integer",
        "value": 1
        }
    ]
}

Send the signed transaction to the blockchain. The response from the sign method must be transferred to the input for the broadcast method.

Sample query

curl -X POST --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'X-Contract-Api-Token' -d '{ \
"type": 104, \
"id": "9fBrL2n5TN473g1gNfoZqaAqAsAJCuHRHYxZpLexL3VP", \
"sender": "3PKyW5FSn4fmdrLcUnDMRHVyoDBxybRgP58", \
"senderPublicKey": "2YvzcVLrqLCqouVrFZynjfotEuPNV9GrdauNpgdWXLsq", \
"fee": 10, \
"timestamp": 1549365736923, \
"proofs": [ \
    "2q4cTBhDkEDkFxr7iYaHPAv1dzaKo5rDaTxPF5VHryyYTXxTPvN9Wb3YrsDYixKiUPXBnAyXzEcnKPFRCW9xVp4v" \
], \
"version": 1, \
"contractId": "2sqPS2VAKmK77FoNakw1VtDTCbDSa7nqh5wTXvJeYGo2", \
"params": [ \
    { \
    "key": "a", \
    "type": "integer", \
    "value": 1 \
    } \
] \
}' 'http://localhost:6862/transactions/broadcast'

Get the result of smart contract execution by its ID.

Sample response

[
    {
        "key": "1+1",
        "type": "integer",
        "value": 2
    }
]