config: create helper for dumping config

With this commit we add a new helper function that recursively turns the
runtime configuration into a flat key/value map that is human-readable,
using the dot notation for nested values that is also used in the config
file or command line flags.

config_test.go

@@ -0,0 +1,48 @@
+package lnd
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/chainreg"
+	"github.com/lightningnetwork/lnd/routing"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	testPassword     = "testpassword"
+	redactedPassword = "[redacted]"
+)
+
+// TestConfigToFlatMap tests that the configToFlatMap function works as
+// expected on the default configuration.
+func TestConfigToFlatMap(t *testing.T) {
+	cfg := DefaultConfig()
+	cfg.BitcoindMode.RPCPass = testPassword
+	cfg.BtcdMode.RPCPass = testPassword
+	cfg.Tor.Password = testPassword
+	cfg.DB.Etcd.Pass = testPassword
+	cfg.DB.Postgres.Dsn = testPassword
+
+	result, err := configToFlatMap(cfg)
+	require.NoError(t, err)
+
+	// Pick a couple of random values to check.
+	require.Equal(t, DefaultLndDir, result["lnddir"])
+	require.Equal(
+		t, fmt.Sprintf("%v", chainreg.DefaultBitcoinTimeLockDelta),
+		result["bitcoin.timelockdelta"],
+	)
+	require.Equal(
+		t, fmt.Sprintf("%v", routing.DefaultAprioriWeight),
+		result["routerrpc.apriori.weight"],
+	)
+	require.Contains(t, result, "routerrpc.routermacaroonpath")
+
+	// Check that sensitive values are not included.
+	require.Equal(t, redactedPassword, result["bitcoind.rpcpass"])
+	require.Equal(t, redactedPassword, result["btcd.rpcpass"])
+	require.Equal(t, redactedPassword, result["tor.password"])
+	require.Equal(t, redactedPassword, result["db.etcd.pass"])
+	require.Equal(t, redactedPassword, result["db.postgres.dsn"])
+}