Author: sandeeppote

Solidity deployment error – ContractNotFound: No contract deployed at address

July 4, 2022 /

At time when the Ganache tool is re-opened all the Transactions and Constracts are reset. Whilst deploying contract you might see the error –

ContractNotFound: No contract deployed at {address}

PS C:\Projects\Blockchain\Solidity\brownie_fundme> brownie run .\scripts\deploy.py --network ganache-local
INFO: Could not find files for the given pattern(s).
Brownie v1.19.0 - Python development framework for Ethereum

BrownieFundmeProject is the active project.
  File "C:\Users\sandeep\.local\pipx\venvs\eth-brownie\lib\site-packages\brownie\_cli\__main__.py", line 64, in main
    importlib.import_module(f"brownie._cli.{cmd}").main()
  File "C:\Users\sandeep\.local\pipx\venvs\eth-brownie\lib\site-packages\brownie\_cli\run.py", line 45, in main
    network.connect(CONFIG.argv["network"])
  File "C:\Users\sandeep\.local\pipx\venvs\eth-brownie\lib\site-packages\brownie\network\main.py", line 55, in connect
    p._load_deployments()
  File "C:\Users\sandeep\.local\pipx\venvs\eth-brownie\lib\site-packages\brownie\project\main.py", line 370, in _load_deployments
    contract = ProjectContract(self, build, build_json.stem)
  File "C:\Users\sandeep\.local\pipx\venvs\eth-brownie\lib\site-packages\brownie\network\contract.py", line 1305, in __init__
    _DeployedContractBase.__init__(self, address, owner, tx)
  File "C:\Users\sandeep\.local\pipx\venvs\eth-brownie\lib\site-packages\brownie\network\contract.py", line 708, in __init__
    raise ContractNotFound(f"No contract deployed at {address}")
ContractNotFound: No contract deployed at 0x7465E5ca8aFeFba39eFD83bd056ACAafa3d16646

Solution-

Delete all the files and folders in Deployment folder as closing the Ganache tool will reset contracts etc. the deployment folder has references to old contract.

Reference-

https://stackoverflow.com/questions/68460396/contractnotfound-no-contract-deployed-at

Add new network in Ganache using brownie for Ethereum Smart Contract local development

June 30, 2022 /

This should show the list of networks available in Brownie.

brownie networks list

In the Ethereum (persistent network) there is no Ganache(local) network

Add a network to Ethereum 

brownie networks add Ethereum ganache-local host=http://127.0.0.1:7545 chainid=1337

Name of the network- ganache-local

host- where ganache endpoint is listening i.e. RPC Server

chainid – for ganache it is 1337

Output–

Install Ganache for Solidity development

June 26, 2022 /

Ganache is the development tool used to run local blockchain for Ethereum development.

Ganache can be used to deploy the contract to local Blockchain. Its a simutated environemnt like Javascript VM when developing on Remix. It helps spin up a local Blockchain.

Ganache UI

Install the Ganache from following location-

https://trufflesuite.com/ganache/

Click the QUICKSTART to get started with Ethereum. By default Ethereum is selected. Ganache can also be used for Corda development

The next screen shows the local Blockchain with the Accounts having 100 ETH and ready to receive the contracts and transactions.

Options in Ganache in later post.

Ganache CLI-

Similar to Ganache UI the local Blockchain node can be setup using CLI.

Install nodejs – https://nodejs.org/en/download/

Check the version of node js 

node -v

Install yarn

npm install --global yarn

Install Ganache CLI

yarn global add ganache-cli

Verify installation by checking the version

ganache-cli --version
Ganache CLI v6.12.2 (ganache-core: 2.13.2)

Use following command to see the Accounts, Transactions, Contracts etc in command line same as UI.

ganache-cli --deterministic

For more CLI options see –

https://www.npmjs.com/package/ganache-cli

Start deploying Contracts, signing and sending transactions to the local Blockchain.

To use Blockchain as a service use-

https://infura.io/

https://www.alchemy.com/

Blockchain Concepts

June 19, 2022 /

Advantages of Blockchain-

  • Decentralised – Having no single point of authority
  • Transperancy and Flexibility
  • Speed and Effeciency
  • Security and Immutability
  • Removal of counterparty risk
  • Trust minimised agreements
  • Hybrid smart conrtract with Chain Link (Oracle)

Terms and Abbrevations used in Blockchain-

DAO’s – Decentralised Autonomous Organization’s

Testnet – are free and for testing smart contracts

Mainnet – cost money and are considered “live”

Faucet – is and application that gives us free test token, like free test Rinkeby Ethereum

Block Explorer – an application that allows us to “view” transactions that happen on a blockchain.

Gas – is a unit of computational measure. The more computation a transaction uses the more “gas” you have to pay for.

Every transaction that happens on-chain pays a “gas fee” to node operators.

The amount of “gas” used and how much you pay depends on how “computationally expensive” your transaction is.

Sending ETH to 1 address would be “cheaper” than sending ETH to 1,000 addresses.

Gwei (giga-wei) – denomination or a small unit of Ether 1 Ether is 1 billion Gwei. It is used to measure cost of transaction i.e. used in the Ethereum network to but and sell goods and services.

Gas – Measure of computation use

Gas Price – How much it costs per unit of gas.

Gas Limit – Max amount of gas in a transaction

Transaction Fee – Gas used X Gas Price i.e. 21,000 gas @ 1GWEI per gas =21,000 GWEI

Gas Price of Ehtereum fluctuates based on the demand of the blockchain. More perople using or want to make transactions, the higher the gas price and therefore the higher the transaction fees.

Gnesis Block – First block in a blockchain

Hash – Unique fixed length string to identify a piece of data

Hash Algorithm – A function or algorithm that computes data into a unique hash.

Mining – The precess of finding the “solution” to the blockchain “problem”. Node get paid for mining blocks.

Block – A list of transactions mined together

Nonce – A “number used once” to find the “solution” to the blockchain problem. It’s also used to define the transaction number for an account/address.

Public Key – Is derived from your private key. Anyone can “see” it, and user it, and user it to verify that a transaction came from you.

Private key – Only know to the keyholder, its used to “sign” transactions.

Elliptic Curve Digital Signature Algorithm (ECDSA) – generates public key using private key.

Signing Transactions – A “one way” process. Someone with a private key signs a transaction by their private key being hashed with their transaction data. Anyone can then verify this new transaction hash with your public key.

Node: Single instance in a decentralized network. Anyone can join the network. Blockchains are resilient. Blockchain nodes keep lists of the transactions that occur. They are immutable- nothing can corrupt them.

—Consensus – is the mechanism used to agree on the state of a blockchain.

Broken into 2 :-

— Chain Selection –

— Sybil Resistance – Proof of work. Block Author, defends on fake blockchains

— — PoW – Minners. Uses lot of electricity and is hence costly.

-Transaction Fees and Block Reward.- compete each other to find the answer to the problems. Whoever finds first get the transaction fees.

Sybil Attack – creates fake accounts to influence the network

51% attack –

Longest Chain Rule

– — PoS — Validators – nodes put up collateral as a sybil resistance mechanism. Uses less energy. Slightly less decentralised.

ABI– ApplicationBinary Interface- tells Solidity how it can interact with another contract. What functions can be called from the contract. Interfaces compile down to ABI.

Python- Class Method

May 20, 2022 /

Class Methods are like Class Varaibles which works on Class but not on object level.

So this methods are bound to class and not object. See class varaibles here

Clas Methods are decorated with @classmethod attribute to the method in class.

This method can be called without creating instance of the class.

See below example definition and usage of class method.

In the above example get_instance_counter() method is decorated as @classmethod and a cls variable is passed. This holdsthe class reference for which the method is called.

The constructor works normal with __init__ method and updates calss variable counter increments the counter when an instance is created. This class variable accessed in the get_instance_counter() method.

You can also provision Python class to have multiple constructor with class method. See here – How to add multiple constructor to Python class?

Dockerfile Best Practice

May 12, 2022 /

Build Modular Images i.e. Decouple applications

Create a seperate image for each application. Containers can talk to each other and can form a single large application and helps to scale each application

Don’t sotre data in Images

Images are read-only layer. When a container or image is deleted the data is lost

Use Cache Busting strategy

Install the repositories and packages together. As the docker file ises layered architecture having a seperate command for updating repositories and packages may not gurantee the repsoitories will be upto date and may result in dependency issue.

Use Version Pinning

When installing packages specifiy which version you want to install as everytime the image is build it will install the latest package where a application may not be compatible. Version pinning will always ensure the image will have specific version which your application supports.

Create slim images

This will help pull the images from which ever repository you are using quickly

Install only necessary or required packages

This will make image slim or with minimal packages and no unwanted packages are installed so every time image is build with minimal packages the build is fast and light weight. Also the containers created from such images are light weight and fast.

Maintain different images for different environements

Development images may contain debug tools and temprorary files required for debugging and bulding your application. However there tools are not required for production images. Hence remvoe any temporary files/folder and such tools for prodcution by creating a seperate image for different environments.

Use multi-stage builds to create images

Multi-stage build helps to or uses multiple FROM statements where each FROM instruction can use a different base, and each of them begins with new stage of the build and everything that is required for application is in the final image leaving behind unwanted files. This will avoid executing any script that was done traditionaly.

Exclude any unwanted files and folders using .dockerignore file

Use .dockerignore to exlcude any unwanted files and folders e.g.:- temp folder etc. this make the image lighter.

Use CMD instructions to run software in Image

Use CMD instructions to run the software contained in your image along with arguments. CMD should be used in JSON format that is the command and parameters should be seperated by comma.

Minimize build times

By avoiding to send unwanted files to the build context using .dockerengine

References –

https://docs.docker.com/develop/develop-images/multistage-build/

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/

Linux and Docker on Ubuntu Series

May 11, 2022 /

Linux basic commands (Ubuntu)

Linux Kernel and hardware

Linux Runlevels

Linux Package Management for Ubuntu

Linux User Management commands

Linux Networking commands

Install Docker on Linux

Linux File Types

Create a file in Linux

How to check the file size in Linux

Compressing and Uncompressing Files in Linux

Searching files and directories in Linux

Search content with pattern in the file in Linux

Search content with pattern in the file in Linux

File Permissions in Linux

Check running services in Linux

DOCKER–

Docker FAQ’s

Install Docker on Ubuntu

Install Docker using install script on Ubuntu

Setup a Docker Swarm

Cache Busting and Version Pinning when building Docker images

Docker storage on Ubuntu

How to start docker in debug mode in Ubuntu

Docker Restart Policies

Use Docker image offline with Save and Load command in Ubuntu

Export Container and Import as Image using Docker in Ubuntu

Create a custom network in docker for communication between containers

Dcoker Security

Docker Best practice

Index and Search OrderCloud Extended Properties

May 9, 2022 /

This article explains usage of extended properties in OrderCloud-

https://ordercloud.io/knowledge-base/extended-properties

But it doesn’t tell about how to index the extended properties to get the search results.

This blog post helps to setup the XP Indices feature already available with the OrderCloud and search such properties.

This example shows extended properties for Categories for which first Catalog needs to setup

1. Create Catalog from Portal (Assume Marketplace is already created)-

Navigate to Product Catalogs => Catalog => Select an operation “Create a new catalog”

Use below JSON or fill in form to create catalog

{
  "ID": "0001",
  "Active": true,
  "Name": "HabitatMaster",
  "Description": "HabitatMaster"
}

Catalog will be created with 201 status

2. Create Catagories from Portal with reference to Catalog Id created previously-

Navigate to Product Catalogs => Categories=> Select an operation “Create a new category”

Use below JSON to create catqagory for Catalog “0001” with the extended property “DisplayType” as “Text”

{
  "ID": "0001-CategoryDisplayText",
  "Active": true,
  "Name": "CategoryDisplayText",
  "Description": "CategoryDisplayText",
  "xp": {
    "DisplayType": "Text"
  }
}

Likewise create another catagory with DisplayType Image as per below JSON-

{
  "ID": "0001-CategoryDisplayImage",
  "Active": true,
  "Name": "CategoryDisplayImage",
  "Description": "CategoryDisplayImage",
  "xp": {
    "DisplayType": "Image"
  }
}

3. Search Category with newly created extended property i.e. DisplayType

First search all categories with Catalog Id “0001”. Following results will be shown-

Now lets try and search with extended properties i.e. Catalog Id “0001” and DisplayType as Text. For this use “Add Filter” option and key as “xp.DisplayType” and Filter Value as “Text”.

This request wont show any results and hence Xp Indices needs to created for Category

4. Create XP Indices

Navigate to Seller => Xp Indices

Indexable resources Catagory “Add Index” => “xp.DisplayType” and Save Changes

Now search the Catagories same as in Step 3 with Filter option and this time you should be able to see the results-

Compressing and Uncompressing Files in Linux

May 3, 2022 /

Compress a file in Linux using tar command

To compress multiple files us tar command with cf option

tar -cf test.tar <<file1>> <<file2>> <<file3>>

To see the content of the tar files use tf option

tar -tf test.tar

To extract the contents from tar file use xf option-

tar -f test.tar

Use zcf command to reduce the file size

tar -zcf testzcf.tar <<file1>> <<file2>>

See the size of test.tar and testzcf.tar file. The content in the tar is same but the size of the testzcf.tar is reduced with zcf command

There are other utlitlies to reduce the file size i.e. to compress files

Use gzip to compress file-

gzip <<file>>

This created filename.gz file. See the size of the firstfile.txt when comperessed

You can also use bzip2 and xz to compress files

Decompress a file

To decompress the gzip file use gunzip command-

You can use bunzip2 and unxz to decompress file

Use Docker Image offline with Save and Load command in Ubuntu

April 29, 2022 /

Docker Save and Load command

At times if you dont want to always pull the image from image registry which takes time to pull if the image’s are heavy, it makes sense to save the image and use it offline. This avoids to always pull the image from the registry.

Save the image once into tar file and reuse the images.

To Save image use follwoing command

First pull the image from repository

docker pull httpd
docker image save httpd -o httpdimage.tar

Get the image from the tar file instead pulling it from the registry

docker image load -i httpdimage.tar