eth/nodeclient: Set contract nonces manually.

[JoeGruffins]

The v0 contract will reuse account nonces if the tx is not yet
confirmed. To avoid that get the next nonce from the light eth node pool
api while holding the nodeClient nonceSendMtx and set manually. Hold the
mutex until the tx has been sent or errors on sending.

closes #1467

[JoeGruffins]

Tested with low fee txn and concurrent sends. Seems to always set the next nonce correctly. This runs the risk of a tx getting stuck ofc if the fee it too low, which is a bigger problem than with utxo based coins, and one that should be considered more, imo.

[martonp]

This LGTM. The code could go into a helper function though to avoid repeating it.

[martonp]

Why not just put this code into txOpts?

[JoeGruffins]

Why not just put this code into txOpts?

I think the mtx needs to be held until after the tx has either made it into the pool or not, so after attempting to send. I'm not sure of the actual behavior, but if it will give you the next nonce before a tx is sent, then if one fails you would be skipping the nonce and no longer be able to send. If it will give you the same nonce until it has a tx in the pool using it, then you would be grabbing the same nonce for multiple txn until one is in the pool.

[JoeGruffins]

I don't think the helper would be much shorter if I want to hold that mutex outside of the sending function.

[chappjc]

Yeah let's run with it as is. The key is holding the nonce mutex until the tx hits txpool.