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 summing up of 2x numbers transferred to the contract entry in call-transactions.

Program listing contract.py on Python:

import json
import sys
import os

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

if __name__ == '__main__':
    command = os.environ['COMMAND']
    tx = json.loads(os.environ['TX'])
    if command == 'CALL':
        a = find_param_value(tx['params'], 'a')
        b = find_param_value(tx['params'], 'b')
        if a is None or b is None: sys.exit(-1)
        print(json.dumps([{
            "key": '{0}+{1}'.format(a, b),
            "type": "integer",
            "value": a + b}], separators=(',', ':')))
    elif command == 'CREATE':
        sys.exit(0)
    else:
        sys.exit(-1)

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” and “b” fields.
Returns the result as a value of fields “{a} + {b}” in json format.

Example of incoming parameters

"params":[
    {
        "key":"a",
        "type":"integer",
        "value":1
    },
    {
        "key":"b",
        "type":"integer",
        "value":2
    }
]

Installing a smart contract¶

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

../../../_images/sum-contract-structure.png

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/sum-contract-kv
docker build -t sum-contract-kv .
docker image tag sum-contract-kv localhost:5000/sum-contract-kv
docker start registry
docker push localhost:5000/sum-contract-kv

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-API-Key: key word' -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-API-Key: key word' -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",
    "type": 104,
    "version": 1,
    "params": [
        {
            "type": "integer",
            "key": "a",
            "value": 1
        },
        {
            "type": "integer",
            "key": "b",
            "value": 100

        }
    ]
}

Sample query

curl -X POST --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'X-API-Key: key word' -d '{ \
    "contractId": "2sqPS2VAKmK77FoNakw1VtDTCbDSa7nqh5wTXvJeYGo2", \
    "fee": 10, \
    "sender": "3PKyW5FSn4fmdrLcUnDMRHVyoDBxybRgP58", \
    "type": 104, \
    "version": 1, \
    "params": [ \
        { \
            "type": "integer", \
            "key": "a", \
            "value": 1 \
        }, \
        { \
            "type": "integer", \
            "key": "b", \
            "value": 100 \
\
        } \
    ] \
}' '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
        },
        {
        "key": "b",
        "type": "integer",
        "value": 100
        }
    ]
}

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-API-Key: key word' -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 \
    }, \
    { \
    "key": "b", \
    "type": "integer", \
    "value": 100 \
    } \
] \
}' 'http://localhost:6862/transactions/broadcast'

Get the result of smart contract execution by its ID.

Sample response

[
    {
        "key": "1+100",
        "type": "integer",
        "value": 101
    }
]