rpc: Implement transaction RPC API

[lexnv]

This PR implements the RPC spec for the transaction methods.

The transaction methods include:

• transaction_unstable_submitAndWatch - Submit and watch an extrinsic via RPC pubsub
• transaction_unstable_unwatch - Unsubscribe

Details

The implementation is adjusting the minimum amount of code to maintain
both the old RPC, while offering support for the new RPC spec.

• The spec states that the RPC shall return an error object only if decoding of the
  transaction fails [here]. However, the RPC will also produce an error if the number
  of resources hits its limit or the number of active subscriptions exceeds the limit.
  The dropped event should be used instead, but this requires patching the jsonrpsee first.

• A validated transaction will enter the tx-pool in the ready or future queues.
  Therefore, those events are converted to the validated event without modifications.

• The tx-pool events: Usurped, Dropped, Invalid are converted to the invalid event.

• The tx-pool FinalityTimeout is converted to the dropped event:
  "if the block the transaction is included in takes too long to be finalized".

Testing Done

• Outdated extrinsic

Ok(Object({"error": String("Invalid transaction: Transaction has a bad signature"), "event": String("invalid")}))

• Invalid extrinsic format

RPC call failed: ErrorObject { code: InvalidParams, message: "0x prefix is missing at line 1 column 3", data: None }

• Valid extrinsic format with incompatible metadata

Ok(Object({"error": String("Verification error: Runtime error: Execution failed: Runtime panicked: Bad input data provided to validate_transaction: Could not decode `ChargeAssetTxPayment::asset_id`:\n\tunexpected first byte decoding Option\n"), "event": String("invalid")}))

• Valid extrinsic life cycle

Ok(Object({"event": String("validated")}))
Ok(Object({"block": Object({"hash": String("0x090969a25a0b6d1b094d41364a0e47cbddf5e94b10800077147f05b3c11b138e"), "index": Number(1)}), "event": String("bestChainBlockIncluded")}))
Ok(Object({"block": Object({"hash": String("0x090969a25a0b6d1b094d41364a0e47cbddf5e94b10800077147f05b3c11b138e"), "index": Number(1)}), "event": String("finalized")}))

Next Steps

• mod tests.rs for transaction API
• report RPC exceeding resource limits and subscription permits as events
• optimize sequential events (inBlock 1, inBlock 2, inBock 3) by submitting only the last event (inBlock 3)

Part of #12071.

polkadot companion: paritytech/polkadot#6058

[tomaka]

I'm not familiar with the code, but all your explanations look good to me! 👍
I'm quite happy with it because the transactions pool is far from being simple.

[skunert]

The dropped event should be used instead, but this requires patching the jsonrpsee first.

Can you elaborate, what needs to be patches in jsonrpsee?

Otherwise the logic looks good to me, just some nitpicks and the missing companion since we use TransactionStatus in other repos too.

[niklasad1]

The spec states that the RPC shall return an error object only if decoding of the
transaction fails [here]. However, the RPC will also produce an error if the number
of resources hits its limit or the number of active subscriptions exceeds the limit.

Yeah but you could disable this on the server as well if needed. That will be like that until we got backpressure :P

The dropped event should be used instead, but this requires patching the jsonrpsee first.

I don't understand this, it should be sent out as an ordinary notification (which you can do via SubscriptionSink::send) and then just drop the SubscriptionSink? However, I see you use the stream API then it's a bit more awkward to do that but can't you just terminate the stream after that occurs?

[skunert]

Looks good!

[niklasad1]

I wonder if we can have a specific type for TxIndex which serializes it as a String instead of having to add this as_string attribute on each usize.

It's easy to mess up...

[niklasad1]

nice job, looks good

[jsdw]

Nice!

[jsdw]

Great job! A couple of nitpicks from me but nothing significant offhand.

[lexnv]

bot merge

[Polkadot-Forum]

This pull request has been mentioned on Polkadot Forum. There might be relevant details there:

https://forum.polkadot.network/t/polkadot-release-analysis/1026/2