How to send transactions using RPC?

Question

I'm developing a client library for Dart. I wonder how can I send transactions using RPC.

If I wanted to send a balance transfer only using RPC how could I do it? What are the steps?

I know that I should encode the data before sending it, but I couldn't figure out what to encode and what RPC method to send.

Answer 1

To send the transaction look at the author_submitExtrinsic and author_submitAndWatchExtrinsic, the latter when using subscriptions and wanting to have access to the processing status.

As to the format, it really depends on the on-chain metadata and the signed extensions that are applied on the extrinsic. However generally, assuming Polkadot/Kusama it would be in the following format -

• compact encoded length
• version + signing bit (as per metadata, currently 0x84 when signed - version 4, high bit indicates that is it signed)
• address of sender (generally MultiAddress, so 33 bytes in length)
• signature of extrinsic payload (generally MultiSignature type, so 65 bytes in length)
• mortal era
• nonce
• tip
• call (indexes and params)

Answer 2

https://github.com/substrate-developer-hub/awesome-substrate#mobile lists at least one option: https://github.com/Pocket4D/Polkadot-Dart

Although at the time I am writing it looks stale and unfinished, sadly. But it can perhaps give you a head start to build what you need. There are a few more here to review too https://github.com/search?q=dart+substrate .

The canonical way to submit transactions aka extrinsics is via the Polkadot.js API, one tool that you may reference for how to do this could be best exemplified in the substrate-api-sidecar.

In rust there is also https://github.com/paritytech/subxt that is worth a look.

Hope these help!