R4R: Load Ledger Device at Runtime

PENDING.md

@@ -79,5 +79,7 @@ BUG FIXES
 * SDK
     * \#1988 Make us compile on OpenBSD (disable ledger) [#1988] (https://github.com/cosmos/cosmos-sdk/issues/1988)
     * \#2105 Fix DB Iterator leak, which may leak a go routine.
+    * [ledger] \#2064 Fix inability to sign and send transactions via the LCD by
+    loading a Ledger device at runtime.
 
 * Tendermint

crypto/ledger.go

@@ -6,13 +6,16 @@ import (
 	ledger "github.com/zondax/ledger-goclient"
 )
 
-// If ledger support (build tag) has been enabled, automically attempt to load
-// and set the ledger device, ledgerDevice, if it has not already been set.
+// If ledger support (build tag) has been enabled, which implies a CGO dependency,
+// set the discoverLedger function which is responsible for loading the Ledger
+// device at runtime or returning an error.
 func init() {
-	device, err := ledger.FindLedger()
-	if err != nil {
-		ledgerDeviceErr = err
-	} else {
-		ledgerDevice = device
+	discoverLedger = func() (LedgerSECP256K1, error) {
+		device, err := ledger.FindLedger()
+		if err != nil {
+			return nil, err
+		}
+
+		return device, nil
 	}
 }

crypto/ledger_secp256k1.go

@@ -1,24 +1,27 @@
 package crypto
 
 import (
-	"errors"
 	"fmt"
 
+	"github.com/pkg/errors"
+
 	secp256k1 "github.com/btcsuite/btcd/btcec"
 	tmcrypto "github.com/tendermint/tendermint/crypto"
 	tmsecp256k1 "github.com/tendermint/tendermint/crypto/secp256k1"
 )
 
 var (
-	ledgerDevice    LedgerSECP256K1
-	ledgerDeviceErr error
-
-	// ErrMissingLedgerDevice is used to reflect that a ledger device load has
-	// not been attempted.
-	ErrMissingLedgerDevice = errors.New("missing ledger device")
+	// discoverLedger defines a function to be invoked at runtime for discovering
+	// a connected Ledger device.
+	discoverLedger discoverLedgerFn
 )
 
 type (
+	// discoverLedgerFn defines a Ledger discovery function that returns a
+	// connected device or an error upon failure. Its allows a method to avoid CGO
+	// dependencies when Ledger support is potentially not enabled.
+	discoverLedgerFn func() (LedgerSECP256K1, error)
+
 	// DerivationPath represents a Ledger derivation path.
 	DerivationPath []uint32
 
@@ -47,18 +50,17 @@ type (
 // CONTRACT: The ledger device, ledgerDevice, must be loaded and set prior to
 // any creation of a PrivKeyLedgerSecp256k1.
 func NewPrivKeyLedgerSecp256k1(path DerivationPath) (tmcrypto.PrivKey, error) {
-	if ledgerDevice == nil {
-		err := ErrMissingLedgerDevice
-		if ledgerDeviceErr != nil {
-			err = ledgerDeviceErr
-		}
+	if discoverLedger == nil {
+		return nil, errors.New("no Ledger discovery function defined")
+	}
 
-		return nil, fmt.Errorf("failed to create PrivKeyLedgerSecp256k1: %v", err)
+	device, err := discoverLedger()
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create PrivKeyLedgerSecp256k1")
 	}
 
-	pkl := &PrivKeyLedgerSecp256k1{Path: path, ledger: ledgerDevice}
+	pkl := &PrivKeyLedgerSecp256k1{Path: path, ledger: device}
 
-	// cache the pubkey for later use
 	pubKey, err := pkl.getPubKey()
 	if err != nil {
 		return nil, err