Ethcontract erroneously waits for transaction even after it was mined

[taminomara]

From slack discussion:

@taminomara:

I've noticed a couple of times when executing methods via ethcontract that they may hang and never resolve even though transaction gets mined successfully (I'm using local chain running in dev mode).

@nlordell:

So, what happens is that:

• Transaction is sent by ethcontract
• Block number is retrieved and is block X
• transaction gets mined and is now block X+1
• Transaction receipt gets retrieved with block number X+1
• ethcontract thinks that it needs to wait for 1 block
• creates a eth_newBlockFilter to get notifications about new blocks
• waits for ever to get notified about new blocks, but they don't come because Geth only mines when a new transcation comes is.

@taminomara:

Interesting. I wonder why we didn't catch it sooner? I guess geth mines some additional blocks?

@nlordell:

I think its because:

• On Ganache, the transaction gets mined immediately, so the race is not possible
• On real nodes, new blocks eventually come in, so worst case we wait an extra block