From fc20f757ecb0761de17c189de4380a0feea405e0 Mon Sep 17 00:00:00 2001
From: Aleksandr Bezobchuk <alex@tendermint.com>
Date: Mon, 27 Aug 2018 18:42:03 -0400
Subject: [PATCH] Load ledger device at runtime

---
 crypto/ledger.go           | 17 ++++++++++-------
 crypto/ledger_secp256k1.go | 31 ++++++++++++++++++-------------
 2 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/crypto/ledger.go b/crypto/ledger.go
index 9d446202f7..5489810bca 100644
--- a/crypto/ledger.go
+++ b/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, 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
 	}
 }
diff --git a/crypto/ledger_secp256k1.go b/crypto/ledger_secp256k1.go
index 8cb175d4f5..5f6bcb1ad7 100644
--- a/crypto/ledger_secp256k1.go
+++ b/crypto/ledger_secp256k1.go
@@ -1,24 +1,26 @@
 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.
+	DiscoverLedgerFn func() (LedgerSECP256K1, error)
+
 	// DerivationPath represents a Ledger derivation path.
 	DerivationPath []uint32
 
@@ -47,18 +49,21 @@ 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
+	var ledgerDevice LedgerSECP256K1
+
+	if DiscoverLedger != nil {
+		device, err := DiscoverLedger()
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to create PrivKeyLedgerSecp256k1")
 		}
 
-		return nil, fmt.Errorf("failed to create PrivKeyLedgerSecp256k1: %v", err)
+		ledgerDevice = device
+	} else {
+		return nil, errors.New("no ledger discovery function defined")
 	}
 
 	pkl := &PrivKeyLedgerSecp256k1{Path: path, ledger: ledgerDevice}
 
-	// cache the pubkey for later use
 	pubKey, err := pkl.getPubKey()
 	if err != nil {
 		return nil, err