From eb03f61dce48de8fbb2051ef210d097aceb35274 Mon Sep 17 00:00:00 2001
From: Tanmay <tanmay.bhattacharya.smit@gmail.com>
Date: Fri, 24 Jan 2025 19:10:59 -0500
Subject: [PATCH] add check for gas price

---
 rpc/types/utils.go      |  5 +++
 rpc/types/utils_test.go | 85 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 rpc/types/utils_test.go

diff --git a/rpc/types/utils.go b/rpc/types/utils.go
index acc5eb553a..65185aea78 100644
--- a/rpc/types/utils.go
+++ b/rpc/types/utils.go
@@ -17,6 +17,7 @@ package types
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"math/big"
 	"strings"
@@ -308,6 +309,10 @@ func CheckTxFee(gasPrice *big.Int, gas uint64, feeCap float64) error {
 	if feeCap == 0 {
 		return nil
 	}
+	// Return an error if gasPrice is nil
+	if gasPrice == nil {
+		return errors.New("gasPrice is nil")
+	}
 	totalfee := new(big.Float).SetInt(new(big.Int).Mul(gasPrice, new(big.Int).SetUint64(gas)))
 	// 1 photon in 10^18 aphoton
 	oneToken := new(big.Float).SetInt(big.NewInt(params.Ether))
diff --git a/rpc/types/utils_test.go b/rpc/types/utils_test.go
new file mode 100644
index 0000000000..890e65be11
--- /dev/null
+++ b/rpc/types/utils_test.go
@@ -0,0 +1,85 @@
+package types_test
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/zeta-chain/node/rpc/types"
+)
+
+func TestCheckTxFee(t *testing.T) {
+	tests := []struct {
+		name     string
+		gasPrice *big.Int
+		gas      uint64
+		feeCap   float64
+		wantErr  bool
+		errMsg   string
+	}{
+		{
+			name:     "valid transaction under cap",
+			gasPrice: big.NewInt(100000000000), // 100 Gwei
+			gas:      21000,                    // Standard ETH transfer
+			feeCap:   1.0,                      // 1 ETH cap
+			wantErr:  false,
+			errMsg:   "",
+		},
+		{
+			name:     "transaction exceeds cap",
+			gasPrice: big.NewInt(500000000000), // 500 Gwei
+			gas:      1000000,                  // Complex contract interaction
+			feeCap:   0.1,                      // 0.1 ETH cap
+			wantErr:  true,
+			errMsg:   "tx fee (0.50 ether) exceeds the configured cap (0.10 ether)",
+		},
+		{
+			name:     "nil gas price",
+			gasPrice: nil,
+			gas:      21000,
+			feeCap:   1.0,
+			wantErr:  true,
+			errMsg:   "gasPrice is nil",
+		},
+		{
+			name:     "zero fee cap",
+			gasPrice: big.NewInt(100000000000),
+			gas:      21000,
+			feeCap:   0,
+			wantErr:  false,
+			errMsg:   "",
+		},
+		{
+			name:     "very low gas price",
+			gasPrice: big.NewInt(1),
+			gas:      21000,
+			feeCap:   1.0,
+			wantErr:  false,
+			errMsg:   "",
+		},
+		{
+			name:     "very high gas price",
+			gasPrice: new(big.Int).Mul(big.NewInt(1e18), big.NewInt(100)), // 100 ETH per gas unit
+			gas:      21000,
+			feeCap:   1000.0,
+			wantErr:  true,
+			errMsg:   "tx fee (2100000.00 ether) exceeds the configured cap (1000.00 ether)",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := types.CheckTxFee(tt.gasPrice, tt.gas, tt.feeCap)
+
+			// Check if we expected an error
+			if (err != nil) != tt.wantErr {
+				t.Errorf("CheckTxFee() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+
+			// If we expected an error, verify the error message
+			if tt.wantErr && err.Error() != tt.errMsg {
+				t.Errorf("CheckTxFee() error message = %v, want %v", err.Error(), tt.errMsg)
+			}
+		})
+	}
+}