6 files changed, 35 insertions, 11 deletions
diff --git a/packages/subproviders/src/index.ts b/packages/subproviders/src/index.ts
index ff28b8a8d..6cc650a4d 100644
--- a/packages/subproviders/src/index.ts
+++ b/packages/subproviders/src/index.ts
@@ -4,6 +4,7 @@ export { ECSignature } from '@0xproject/types';
 
 import { LedgerEthereumClient } from './types';
 
+export { prependSubprovider } from './utils/subprovider_utils';
 export { EmptyWalletSubprovider } from './subproviders/empty_wallet_subprovider';
 export { FakeGasEstimateSubprovider } from './subproviders/fake_gas_estimate_subprovider';
 export { InjectedWeb3Subprovider } from './subproviders/injected_web3';
diff --git a/packages/subproviders/src/subproviders/ledger.ts b/packages/subproviders/src/subproviders/ledger.ts
index 347eda55f..467299db0 100644
--- a/packages/subproviders/src/subproviders/ledger.ts
+++ b/packages/subproviders/src/subproviders/ledger.ts
@@ -113,9 +113,12 @@ export class LedgerSubprovider extends BaseWalletSubprovider {
         const tx = new EthereumTx(txParams);
 
         // Set the EIP155 bits
-        tx.raw[6] = Buffer.from([this._networkId]); // v
-        tx.raw[7] = Buffer.from([]); // r
-        tx.raw[8] = Buffer.from([]); // s
+        const vIndex = 6;
+        tx.raw[vIndex] = Buffer.from([this._networkId]); // v
+        const rIndex = 7;
+        tx.raw[rIndex] = Buffer.from([]); // r
+        const sIndex = 8;
+        tx.raw[sIndex] = Buffer.from([]); // s
 
         const txHex = tx.serialize().toString('hex');
         try {
@@ -127,7 +130,8 @@ export class LedgerSubprovider extends BaseWalletSubprovider {
             tx.v = Buffer.from(result.v, 'hex');
 
             // EIP155: v should be chain_id * 2 + {35, 36}
-            const signedChainId = Math.floor((tx.v[0] - 35) / 2);
+            const eip55Constant = 35;
+            const signedChainId = Math.floor((tx.v[0] - eip55Constant) / 2);
             if (signedChainId !== this._networkId) {
                 await this._destroyLedgerClientAsync();
                 const err = new Error(LedgerSubproviderErrors.TooOldLedgerFirmware);
@@ -169,8 +173,10 @@ export class LedgerSubprovider extends BaseWalletSubprovider {
                 fullDerivationPath,
                 ethUtil.stripHexPrefix(data),
             );
-            const v = result.v - 27;
-            let vHex = v.toString(16);
+            const lowestValidV = 27;
+            const v = result.v - lowestValidV;
+            const hexBase = 16;
+            let vHex = v.toString(hexBase);
             if (vHex.length < 2) {
                 vHex = `0${v}`;
             }
diff --git a/packages/subproviders/src/subproviders/nonce_tracker.ts b/packages/subproviders/src/subproviders/nonce_tracker.ts
index 907330111..345e5e975 100644
--- a/packages/subproviders/src/subproviders/nonce_tracker.ts
+++ b/packages/subproviders/src/subproviders/nonce_tracker.ts
@@ -93,7 +93,8 @@ export class NonceTrackerSubprovider extends Subprovider {
         // Increment the nonce from the previous successfully submitted transaction
         let nonce = ethUtil.bufferToInt(transaction.nonce);
         nonce++;
-        let nextHexNonce = nonce.toString(16);
+        const hexBase = 16;
+        let nextHexNonce = nonce.toString(hexBase);
         if (nextHexNonce.length % 2) {
             nextHexNonce = `0${nextHexNonce}`;
         }
diff --git a/packages/subproviders/src/subproviders/subprovider.ts b/packages/subproviders/src/subproviders/subprovider.ts
index 56d2381a0..cb6dffc4a 100644
--- a/packages/subproviders/src/subproviders/subprovider.ts
+++ b/packages/subproviders/src/subproviders/subprovider.ts
@@ -13,10 +13,11 @@ export abstract class Subprovider {
     // Ported from: https://github.com/MetaMask/provider-engine/blob/master/util/random-id.js
     private static _getRandomId(): number {
         const extraDigits = 3;
+        const baseTen = 10;
         // 13 time digits
-        const datePart = new Date().getTime() * Math.pow(10, extraDigits);
+        const datePart = new Date().getTime() * Math.pow(baseTen, extraDigits);
         // 3 random digits
-        const extraPart = Math.floor(Math.random() * Math.pow(10, extraDigits));
+        const extraPart = Math.floor(Math.random() * Math.pow(baseTen, extraDigits));
         // 16 digits
         return datePart + extraPart;
     }
diff --git a/packages/subproviders/src/utils/subprovider_utils.ts b/packages/subproviders/src/utils/subprovider_utils.ts
new file mode 100644
index 000000000..24ebedd06
--- /dev/null
+++ b/packages/subproviders/src/utils/subprovider_utils.ts
@@ -0,0 +1,15 @@
+import ProviderEngine = require('web3-provider-engine');
+
+import { Subprovider } from '../subproviders/subprovider';
+
+/**
+ * Prepends a subprovider to a provider
+ * @param provider    Given provider
+ * @param subprovider Subprovider to prepend
+ */
+export function prependSubprovider(provider: ProviderEngine, subprovider: Subprovider): void {
+    subprovider.setEngine(provider);
+    // HACK: We use implementation details of provider engine here
+    // https://github.com/MetaMask/provider-engine/blob/master/index.js#L68
+    (provider as any)._providers = [subprovider, ...(provider as any)._providers];
+}
diff --git a/packages/subproviders/src/utils/wallet_utils.ts b/packages/subproviders/src/utils/wallet_utils.ts
index cd5cd9ba0..c36fdb9fc 100644
--- a/packages/subproviders/src/utils/wallet_utils.ts
+++ b/packages/subproviders/src/utils/wallet_utils.ts
@@ -30,10 +30,10 @@ class DerivedHDKeyInfoIterator implements IterableIterator<DerivedHDKeyInfo> {
             baseDerivationPath,
             derivationPath: fullDerivationPath,
         };
-        const done = this._index === this._searchLimit;
+        const isDone = this._index === this._searchLimit;
         this._index++;
         return {
-            done,
+            done: isDone,
             value: derivedKey,
         };
     }