client/asset/eth: SwapConfirmations

[buck54321]

Add an asset version argument to (Wallet).SwapConfirmations and implement the method for eth.

[chappjc]

Presently eth's (*swapReceipt).Contract() dex.Bytes returns a slice that contains the secret hash, and this is shoe-horned into MatchProof.Script.

What if it returned a slice that was a concatenation of contract version and secret hash, so that client.asset.Receipt.Contract(), which is assigned to proof.Script, has this info. It's already not a script at all as implied by the MatchProof.Script field name, and it's intended to be an opaque blob for multi-asset support anyway, so why not have it encode the version too?

That is, we're already freely reinterpreting the Receipt.Contract method, so I'd just assume we use it to convey all the info needed about this contract-swap rather than add an arg to SwapConfirmations, which without close examination is kind of a head-scratcher and in fact of no use to existing assets.

[buck54321]

Nice. Done.

[chappjc]

Looking good in this method, and it does seem to be alright if the contract dex.Bytes arg encoded both the asset version and the secret hash. Open to that?

[chappjc]

i.e. concept: bbc9d81

func (eth *ExchangeWallet) SwapConfirmations(ctx context.Context, _ dex.Bytes, contractData dex.Bytes,
	_ time.Time) (confs uint32, spent bool, err error) {

	if len(contractData) != 36 {
		return 0, false, fmt.Errorf("invalid contract data")
	}

	// contractData fully specifies this swap in terms of which contract version
	// is used and the secret hash that keys the unique swap.
	assetVersion := binary.BigEndian.Uint32(contractData[:4])
	var secretHash [32]byte
	copy(secretHash[:], contractData[4:])

	swapData, err := eth.node.swap(ctx, secretHash, assetVersion)
	if err != nil {
		return 0, false, fmt.Errorf("error finding swap state: %w", err)
	}

	if swapData.State == dexeth.SSNone {
		return 0, false, asset.CoinNotFoundError
	}

	hdr, err := eth.node.bestHeader(ctx)
	if err != nil {
		return 0, false, fmt.Errorf("error fetching best header: %w", err)
	}

	spent = swapData.State >= dexeth.SSRedeemed
	confs = uint32(hdr.Number.Uint64() - swapData.BlockHeight + 1)

	return
}