client/asset/eth: token prefactor

Preparing for tokens.

Moves contractor from nodeClient to ExchangeWallet. The changes the
ethFetcher API quite a bit, but is overall a simplification. To accomplish
this, I moved the nonceSendMtx to from nodeClient to ExchangeWallet too.
Nonce generation and signing is moved into nodeClient.txOpts to dedupe.

Use block headers instead of full blocks for tip monitoring.

Simplify fundingCoin and eliminate fundingCoinID.

Simplify tests using more consts and simpler structs.

client/asset/eth/contractor.go

@@ -22,7 +22,6 @@ import (
 	"github.com/ethereum/go-ethereum/accounts/abi/bind"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
-	"github.com/ethereum/go-ethereum/ethclient"
 )
 
 // contractor is a translation layer between the abigen bindings and the DEX app.
@@ -38,14 +37,14 @@ type contractor interface {
 	estimateRefundGas(ctx context.Context, secretHash [32]byte) (uint64, error)
 	isRedeemable(secretHash, secret [32]byte) (bool, error)
 	// incomingValue checks if the transaction redeems or refunds to the
-	// contract and sums the incoming value. It is not an error if the
+	// contract and returns the incoming value. It is not an error if the
 	// transaction does not pay to the contract, and the value returned in that
 	// case will always be zero.
 	incomingValue(context.Context, *types.Transaction) (uint64, error)
 	isRefundable(secretHash [32]byte) (bool, error)
 }
 
-type contractorConstructor func(net dex.Network, addr common.Address, ec *ethclient.Client) (contractor, error)
+type contractorConstructor func(net dex.Network, addr common.Address, cb bind.ContractBackend) (contractor, error)
 
 type contractV0 interface {
 	Initiate(opts *bind.TransactOpts, initiations []swapv0.ETHSwapInitiation) (*types.Transaction, error)
@@ -61,24 +60,24 @@ type contractV0 interface {
 type contractorV0 struct {
 	contractV0   // *swapv0.ETHSwap
 	abi          *abi.ABI
-	ec           *ethclient.Client
+	cb           bind.ContractBackend
 	contractAddr common.Address
 	acctAddr     common.Address
 }
 
-func newV0contractor(net dex.Network, acctAddr common.Address, ec *ethclient.Client) (contractor, error) {
+func newV0Contractor(net dex.Network, acctAddr common.Address, cb bind.ContractBackend) (contractor, error) {
 	contractAddr, exists := dexeth.ContractAddresses[0][net]
 	if !exists || contractAddr == (common.Address{}) {
 		return nil, fmt.Errorf("no contract address for version 0, net %s", net)
 	}
-	c, err := swapv0.NewETHSwap(contractAddr, ec)
+	c, err := swapv0.NewETHSwap(contractAddr, cb)
 	if err != nil {
 		return nil, err
 	}
 	return &contractorV0{
 		contractV0:   c,
 		abi:          dexeth.ABIs[0],
-		ec:           ec,
+		cb:           cb,
 		contractAddr: contractAddr,
 		acctAddr:     acctAddr,
 	}, nil
@@ -189,7 +188,7 @@ func (c *contractorV0) estimateRedeemGas(ctx context.Context, secrets [][32]byte
 		return 0, err
 	}
 
-	return c.ec.EstimateGas(ctx, ethereum.CallMsg{
+	return c.cb.EstimateGas(ctx, ethereum.CallMsg{
 		From: c.acctAddr,
 		To:   &c.contractAddr,
 		Data: data,
@@ -202,7 +201,7 @@ func (c *contractorV0) estimateRefundGas(ctx context.Context, secretHash [32]byt
 		return 0, fmt.Errorf("unexpected error packing abi: %v", err)
 	}
 
-	return c.ec.EstimateGas(ctx, ethereum.CallMsg{
+	return c.cb.EstimateGas(ctx, ethereum.CallMsg{
 		From: c.acctAddr,
 		To:   &c.contractAddr,
 		Data: data,
@@ -226,7 +225,7 @@ func (c *contractorV0) estimateInitGas(ctx context.Context, n int) (uint64, erro
 		return 0, nil
 	}
 
-	return c.ec.EstimateGas(ctx, ethereum.CallMsg{
+	return c.cb.EstimateGas(ctx, ethereum.CallMsg{
 		From:  c.acctAddr,
 		To:    &c.contractAddr,
 		Value: big.NewInt(int64(n)),
@@ -262,5 +261,5 @@ func (c *contractorV0) incomingValue(ctx context.Context, tx *types.Transaction)
 }
 
 var contractorConstructors = map[uint32]contractorConstructor{
-	0: newV0contractor,
+	0: newV0Contractor,
 }