TxDecoder as Middleware

[amaury1093]

Summary

Refactor tx decoding logic as a TxDecoderMiddleware. ref: #10484 (comment)

Problem Definition

With the BaseApp middleware refactor (#9996), BaseApp should be as slim as possible.

Currently, BaseApp still does tx decoding (see its private txDecoder field). We can move this logic into a middleware

Proposal

Create a TxDecoderMiddleware. It will:

• Look if both the tx.Request.Tx and tx.Request.TxBytes are set. If both are empty, error. If Txx is empty, then decode from TxBytes.
  • In practice, txs coming from ABCI Check/DeliverTx will have TxBytes set, so the middleware will decode.

Pros:

• Baseapp only handles tx bytes, is agnostic what the bytes mean
• Modular

Cons:

• TxDecoderMiddleware needs to be in the middleware chain (and quite high), it's not an optional middleware

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned