lntest+lnd_test: add Connect and Disconnect miner for BackendCfgs

This commit gives the current chainbackend the ability to connect and
disconnect the chain backend at will. We do this to let the chain
backend initiate the connection to the miner, not the other way around.

This is a preparation for using Neutrino as a backend, as it only allows
making outbound connections.

We must also move the setup of the chainbackend to after to miner, to
know the address to connect to.

lntest/btcd.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 
+	"github.com/btcsuite/btcd/btcjson"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/integration/rpctest"
 	"github.com/btcsuite/btcd/rpcclient"
@@ -13,14 +14,23 @@ import (
 // logDir is the name of the temporary log directory.
 const logDir = "./.backendlogs"
 
+// perm is used to signal we want to establish a permanent connection using the
+// btcd Node API.
+//
+// NOTE: Cannot be const, since the node API expects a reference.
+var perm = "perm"
+
 // BtcdBackendConfig is an implementation of the BackendConfig interface
 // backed by a btcd node.
 type BtcdBackendConfig struct {
 	// rpcConfig houses the connection config to the backing btcd instance.
 	rpcConfig rpcclient.ConnConfig
 
-	// p2pAddress is the p2p address of the btcd instance.
-	p2pAddress string
+	// harness is the backing btcd instance.
+	harness *rpctest.Harness
+
+	// minerAddr is the p2p address of the miner to connect to.
+	minerAddr string
 }
 
 // GenArgs returns the arguments needed to be passed to LND at startup for
@@ -37,21 +47,27 @@ func (b BtcdBackendConfig) GenArgs() []string {
 	return args
 }
 
-// P2PAddr returns the address of this node to be used when connection over the
-// Bitcoin P2P network.
-func (b BtcdBackendConfig) P2PAddr() string {
-	return b.p2pAddress
+// ConnectMiner is called to establish a connection to the test miner.
+func (b BtcdBackendConfig) ConnectMiner() error {
+	return b.harness.Node.Node(btcjson.NConnect, b.minerAddr, &perm)
+}
+
+// DisconnectMiner is called to disconnect the miner.
+func (b BtcdBackendConfig) DisconnectMiner() error {
+	return b.harness.Node.Node(btcjson.NRemove, b.minerAddr, &perm)
 }
 
 // NewBtcdBackend starts a new rpctest.Harness and returns a BtcdBackendConfig
-// for that node.
-func NewBtcdBackend() (*BtcdBackendConfig, func(), error) {
+// for that node. miner should be set to the P2P address of the miner to
+// connect to.
+func NewBtcdBackend(miner string) (*BtcdBackendConfig, func(), error) {
 	args := []string{
 		"--rejectnonstd",
 		"--txindex",
 		"--trickleinterval=100ms",
 		"--debuglevel=debug",
 		"--logdir=" + logDir,
+		"--connect=" + miner,
 	}
 	netParams := &chaincfg.SimNetParams
 	chainBackend, err := rpctest.New(netParams, nil, args)
@@ -64,8 +80,9 @@ func NewBtcdBackend() (*BtcdBackendConfig, func(), error) {
 	}
 
 	bd := &BtcdBackendConfig{
-		rpcConfig:  chainBackend.RPCConfig(),
-		p2pAddress: chainBackend.P2PAddress(),
+		rpcConfig: chainBackend.RPCConfig(),
+		harness:   chainBackend,
+		minerAddr: miner,
 	}
 
 	cleanUp := func() {