From f882de62f3071c259d9948b052e6c3bdca4fd767 Mon Sep 17 00:00:00 2001
From: Chris Maree <christopher.maree@gmail.com>
Date: Fri, 7 Aug 2020 16:15:23 +0200
Subject: [PATCH] Liquidator & disputer bot: Improve bot gas estimation (#1801)

---
 disputer/disputer.js     | 15 +++++++++++----
 liquidator/liquidator.js | 12 +++++++++---
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/disputer/disputer.js b/disputer/disputer.js
index fd5534ead9..1e6e995e40 100644
--- a/disputer/disputer.js
+++ b/disputer/disputer.js
@@ -42,6 +42,9 @@ class Disputer {
     this.toBN = this.web3.utils.toBN;
     this.utf8ToHex = this.web3.utils.utf8ToHex;
 
+    // Multiplier applied to Truffle's estimated gas limit for a transaction to send.
+    this.GAS_LIMIT_BUFFER = 1.25;
+
     // Default config settings. Disputer deployer can override these settings by passing in new
     // values via the `config` input object. The `isValid` property is a function that should be called
     // before resetting any config settings. `isValid` must return a Boolean.
@@ -128,8 +131,10 @@ class Disputer {
       const dispute = this.empContract.methods.dispute(disputeableLiquidation.id, disputeableLiquidation.sponsor);
 
       // Simple version of inventory management: simulate the transaction and assume that if it fails, the caller didn't have enough collateral.
+      let gasLimit, totalPaid;
       try {
-        await dispute.call({ from: this.account, gasPrice: this.gasEstimator.getCurrentFastPrice() });
+        totalPaid = await dispute.call({ from: this.account });
+        gasLimit = Math.floor((await dispute.estimateGas({ from: this.account })) * this.GAS_LIMIT_BUFFER);
       } catch (error) {
         this.logger.error({
           at: "Disputer",
@@ -137,6 +142,7 @@ class Disputer {
           disputer: this.account,
           sponsor: disputeableLiquidation.sponsor,
           liquidation: disputeableLiquidation,
+          totalPaid,
           error
         });
         continue;
@@ -144,7 +150,7 @@ class Disputer {
 
       const txnConfig = {
         from: this.account,
-        gas: this.txnGasLimit,
+        gas: Math.min(gasLimit, this.txnGasLimit),
         gasPrice: this.gasEstimator.getCurrentFastPrice()
       };
 
@@ -223,9 +229,10 @@ class Disputer {
       const withdraw = this.empContract.methods.withdrawLiquidation(liquidation.id, liquidation.sponsor);
 
       // Confirm that dispute has eligible rewards to be withdrawn.
-      let withdrawAmount;
+      let withdrawAmount, gasLimit;
       try {
         withdrawAmount = revertWrapper(await withdraw.call({ from: this.account }));
+        gasLimit = Math.floor((await withdraw.estimateGas({ from: this.account })) * this.GAS_LIMIT_BUFFER);
         if (withdrawAmount === null) {
           throw new Error("Simulated reward withdrawal failed");
         }
@@ -241,7 +248,7 @@ class Disputer {
 
       const txnConfig = {
         from: this.account,
-        gas: this.txnGasLimit,
+        gas: Math.min(gasLimit, this.txnGasLimit),
         gasPrice: this.gasEstimator.getCurrentFastPrice()
       };
       this.logger.debug({
diff --git a/liquidator/liquidator.js b/liquidator/liquidator.js
index 8ced2d1f4d..a871cdf24d 100644
--- a/liquidator/liquidator.js
+++ b/liquidator/liquidator.js
@@ -52,6 +52,9 @@ class Liquidator {
     this.fromWei = this.web3.utils.fromWei;
     this.utf8ToHex = this.web3.utils.utf8ToHex;
 
+    // Multiplier applied to Truffle's estimated gas limit for a transaction to send.
+    this.GAS_LIMIT_BUFFER = 1.25;
+
     // Default config settings. Liquidator deployer can override these settings by passing in new
     // values via the `config` input object. The `isValid` property is a function that should be called
     // before resetting any config settings. `isValid` must return a Boolean.
@@ -248,8 +251,10 @@ class Liquidator {
       );
 
       // Simple version of inventory management: simulate the transaction and assume that if it fails, the caller didn't have enough collateral.
+      let gasLimit;
       try {
         await liquidation.call({ from: this.account });
+        gasLimit = Math.floor((await liquidation.estimateGas({ from: this.account })) * this.GAS_LIMIT_BUFFER);
       } catch (error) {
         this.logger.error({
           at: "Liquidator",
@@ -268,7 +273,7 @@ class Liquidator {
 
       const txnConfig = {
         from: this.account,
-        gas: this.txnGasLimit,
+        gas: Math.min(gasLimit, this.txnGasLimit),
         gasPrice: this.gasEstimator.getCurrentFastPrice()
       };
       this.logger.debug({
@@ -356,9 +361,10 @@ class Liquidator {
       const withdraw = this.empContract.methods.withdrawLiquidation(liquidation.id, liquidation.sponsor);
 
       // Confirm that liquidation has eligible rewards to be withdrawn.
-      let withdrawAmount;
+      let withdrawAmount, gasLimit;
       try {
         withdrawAmount = revertWrapper(await withdraw.call({ from: this.account }));
+        gasLimit = Math.floor((await withdraw.estimateGas({ from: this.account })) * this.GAS_LIMIT_BUFFER);
         if (!withdrawAmount) {
           throw new Error("Simulated reward withdrawal failed");
         }
@@ -374,7 +380,7 @@ class Liquidator {
 
       const txnConfig = {
         from: this.account,
-        gas: this.txnGasLimit,
+        gas: Math.min(gasLimit, this.txnGasLimit),
         gasPrice: this.gasEstimator.getCurrentFastPrice()
       };
       this.logger.debug({