we expect unspent outputs but play it safe

[antiochp]

Related: #516

We call the get_unspent_outputs api and expect to receive a collection of unspent outputs.
This is a reasonable assumption but we are brittle on the receiving/parsing side as each output in the response must contain a block height. If we receive a spent output for any reason the wallet is rendered inoperable as we can no longer refresh outputs.

This PR adds a (hopefully redundant) level of robustness by explicitly filtering out spent outputs from the list returned by the api.

See #516 for some background where the node api was inadvertently changed to return spent and unspent outputs, causing the wallet to fail.

[quentinlesceller]

Any idea why we are receiving a spent output? Shouldn't we filter them server side instead (or also)?

[antiochp]

Any idea why we are receiving a spent output? Shouldn't we filter them server side instead (or also)?

This was actually against a node running with code from mimblewimble/grin#3428
So this was an unintentional break of the api contract (returned spent outputs when it should not).

But - I think we should filter these on both sides. The wallet should make as few assumptions as possible regarding data returned by the node.
So we should filter client side also.

[quentinlesceller]

👍 then