getrawtransaction JSON-RPC method

[mpguerra]

Motivation

lightwalletd uses the getrawtransaction JSON-RPC method in response to wallet queries.

So this RPC needs to be fast:

• Store transactions in a separate database index #3151
• Use smaller keys for block and transaction database indexes #3152

Assumptions

lightwalletd doesn't need witnessed mempool transaction IDs for Orchard (UnminedTxId).
https://discord.com/channels/809218587167293450/809250822579028008/943326658042163270

Required Fields

The method is documented here: https://zcash.github.io/rpc/getrawtransaction.html

lightwalletd uses these arguments:

• txid and verbosity = 0: https://github.com/zcash/lightwalletd/blob/master/frontend/service.go#L431
• txid and verbosity = 1: https://github.com/zcash/lightwalletd/blob/master/frontend/service.go#L247

And only these fields are used by lightwalletd:

• hex, height: https://github.com/zcash/lightwalletd/blob/master/common/common.go#L117
• unmined transaction height: https://github.com/zcash/lightwalletd/blob/83bb19918fb36a5f6d5013fba7938daf3d73db1d/walletrpc/service.proto#L39

Field list:

{
  "hex" : "data",       (string) The serialized, hex-encoded data for 'txid'
  "height" : n,             (numeric) The block height of the transaction in the best chain, or -1 if not in the best chain
}

Tasks

• Implement the RPC method
• Add RPC acceptance tests to CI
• Test that the RPC method works with lightwalletd

API Reference

We plan to use jsonrpc_core with:

• jsonrpc_http_server
• jsonrpc-derive

Example Code

Here are examples of:

• declaring RPC methods as Rust functions

[ftm1000]

Hey team! Please add your planning poker estimate with ZenHub @conradoplg @dconnolly @gustavovalverde @jvff @oxarbitrage @teor2345 @upbqdn

[teor2345]

@ftm1000 @conradoplg this ticket doesn't depend on the transaction database indexes.

It will perform poorly until we do #3151, but it should be ok for testing.