Sidecar and TxWrapper Integration

This is a guide to using Substrate API Sidecar and TxWrapper to construct, sign, and submit a transaction to a Substrate-based chain.

Note: This will work on any Substrate-based chain, but for now is only set up to work on Polkadot, Kusama, or a development chain using Polkadot's SS58 address encoding.

Instructions

Tested on:

• Polkadot v1,000,001
• Sidecar v17.3.4
• Txwrapper Polkadot v7.2.0

Start a Node

If you have access to a sidecar endpoint, then you can skip this step.

Start a Polkadot node. Can be local development node (--dev) or connect to mainnet. See the Polkadot repo for instructions.

Set up Sidecar

Clone the sidecar repo and start with yarn; yarn build; yarn start;. It will connect to localhost by default and start an http server on port 8080.

Run

The main function will:

1. Connect to the Sidecar and collect all the necessary information to construct a transaction.
2. Create a signing payload for the transaction(s) specified in transaction.json.
3. Wait for you to sign the payload.
4. Submit the transaction.

Construction

You will need to create a transaction.json file. An example is provided. This is where you enter the base info (like IP/port for Sidecar) and an array of transactions you want to construct.

Run yarn start and you will get:

Chain Name: Polkadot
Spec Name:  polkadot
Network Version: 1000001
Transaction Version: 24

Transaction Details:
  Sending Account:   15oF4uVJwmo4TdGW7VfQxNLavjCXviqxT9S1MgbjMNHr6Sp5
  Receiving Account: 14E5nqKAp3oAJcmzgZhUD2RcptBeUBScxKHgJKU4HPNcKVf3
  Amount: 1000000000000
  Tip:    0

Signing Payload: 0xa005038eaf04151687736326c9fea17e25fc5287613693c912909cb226aa4794f26a48070010a5d4e895030000f00300003a5dacb3a8725d578ab4b1457764e960a86b17720c3d39086c3b0872122b7a41f837b149dcb20f92540a027e58aab0554d2d42f36887f33a5e6a85ebdd0f13d8

Signature:

This will wait for you to sign the payload.

Signing

You can sign the payload in any way you like. Ideally, you should do this on a secure, offline device. A signing script is provided to use for testing.

You also need the metadata from the first part, but this only changes on runtime upgrades. This repo contains a file with metadata for well known runtimes, like Polkadot, with the name <specName>Metadata, e.g. polkadotMetadata.

Create a new file called key.json (there is an example provided) that exports a signing key and type. In here you can put your signing key. It can be a 12 word phrase or secret seed. Or, in the case of a dev chain, just //Alice:

Run yarn sign and enter the signing payload from the last step to get a signature:

$ yarn sign

Payload: <enter the signing payload here>

Signature: 0x014679aaf0589f456f57875837c3c3f9747dee901304e05fe9511eece5bfd68c1e7443ff6d476f170d80cbbabae5f6bd3cf3d486663fe8f68d48e8ea7c70edc18d

Submission

Paste this signature into the terminal that is waiting, press enter, and it will submit the transaction to your node.