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Co-authored-by: Mudit Gupta <guptamudit@ymail.com>
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Fork off substrate

This script allows bootstrapping a new substrate chain with the current state of a live chain. Using this, you can create a fork of Polkadot, Kusama and other substrate chain for development purposes.

Usage

  1. Clone this repository and install dependencies

    git clone https://github.com/maxsam4/fork-off-substrate.git
    cd fork-off-substrate
    npm i
  2. Create a folder called data inside the top folder (fork-off-substrate).

    mkdir data
  3. Copy the executable/binary of your substrate based node inside the data folder and rename it to binary.

  4. Copy the runtime WASM blob of your substrate based blockchain to the data folder and rename it to runtime.wasm. To get the WASM blob, compile your blockchain and look for ./target/release/wbuild/runtime/runtime.compact.wasm. If you are forking Polkadot/Kusama/Westend, you can download the WASM blobs from Polkadot's release page.

  5. If your substrate chain uses additional custom types than what are available in polkadot.js, define them in a JSON file of format { "types": { <YOUR_TYPES> } }. Copy the file to the data folder and rename it to schema.json.

  6. Either run a full node for your blockchain locally(Recommended) or have an external endpoint handy.

  7. Run the script

    • If using a local node, simply run the script using

      npm start
    • If you are using an external/non-default endpoint, you need to provide it to the script via the HTTP_RPC_ENDPOINT environment variable

      HTTP_RPC_ENDPOINT=https://example.com npm start
  8. You should have the genesis file for the forked chain inside the data folder. It will be called fork.json.

  9. You can now run a new chain using this genesis file

    ./binary --chain fork.json --alice

Configuration

The script can be tweaked and configured using various environment variables -

Environment Variable Effects Default value
HTTP_RPC_ENDPOINT HTTP RPC endpoint that should be used to query state http://localhost:9933
FORK_CHUNKS_LEVEL Determines how many chunks to split the RPC download in. Effect is exponential, recommended value for most is 1. You can try 0 for small chains and 2 for large chains for potential speed improvements 1
ORIG_CHAIN Chain to use as the original chain. $default_of_the_binary
FORK_CHAIN Chain to use as base for the forked chain. dev
ALICE If set, the script will replace the chain's sudo account with //Alice NULL
QUICK_MODE If set, it parallelizes the data download from the RPC endpoint NULL

Read more

If you would like to understand how this script works, please read this blog post

Using Docker

Build the image

docker build -t fork-off-substrate .

Run

BINARY=/full/path/to/your/linux/binary
HTTP_RPC_ENDPOINT=http://localhost:9933
docker run --rm -it \
    -e HTTP_RPC_ENDPOINT=$HTTP_RPC_ENDPOINT \
    -v "$BINARY":/data/binary
    fork-off-substrate

Credits

This script is based on a script shared in the substrate riot channel

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This script allows bootstrapping a new substrate chain with the current state of a live chain

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