chore(lib/common) implement MustHexToBigInt (ChainSafe#1547)

* implement MustHexToBigInt

* add tests for panics

* clean-up string checking

dot/import.go

@@ -21,7 +21,6 @@ import (
 	"encoding/json"
 	"errors"
 	"io/ioutil"
-	"math/big"
 	"path/filepath"
 
 	"github.com/ChainSafe/gossamer/dot/state"
@@ -97,8 +96,7 @@ func newHeaderFromFile(filename string) (*types.Header, error) {
 		return nil, errors.New("invalid number field in header JSON")
 	}
 
-	numBytes := common.MustHexToBytes(hexNum)
-	num := big.NewInt(0).SetBytes(numBytes)
+	num := common.MustHexToBigInt(hexNum)
 
 	parentHashStr, ok := jsonHeader["parentHash"].(string)
 	if !ok {

lib/common/common.go

@@ -21,6 +21,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"io"
+	"math/big"
 	"strconv"
 	"strings"
 )
@@ -103,6 +104,32 @@ func MustHexToBytes(in string) []byte {
 	return out
 }
 
+// MustHexToBigInt turns a 0x prefixed hex string into a big.Int
+// it panic if it cannot decode the string
+func MustHexToBigInt(in string) *big.Int {
+	if len(in) < 2 {
+		panic("invalid string")
+	}
+
+	if strings.Compare(in[:2], "0x") != 0 {
+		panic(ErrNoPrefix)
+	}
+
+	in = in[2:]
+
+	// Ensure we have an even length
+	if len(in)%2 != 0 {
+		in = "0" + in
+	}
+
+	out, err := hex.DecodeString(in)
+	if err != nil {
+		panic(err)
+	}
+
+	return big.NewInt(0).SetBytes(out)
+}
+
 // BytesToHex turns a byte slice into a 0x prefixed hex string
 func BytesToHex(in []byte) string {
 	s := hex.EncodeToString(in)

lib/common/common_test.go

@@ -18,8 +18,12 @@ package common
 
 import (
 	"bytes"
+	"math/big"
 	"reflect"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestStringToInts(t *testing.T) {
@@ -182,3 +186,32 @@ func TestSwapNibbles(t *testing.T) {
 		}
 	}
 }
+
+func TestMustHexToBigInt(t *testing.T) {
+	tests := []struct {
+		in  string
+		out *big.Int
+	}{
+		{"0x0", big.NewInt(0).SetBytes([]byte{0})},
+		{"0x00", big.NewInt(0).SetBytes([]byte{0})},
+		{"0x1", big.NewInt(1)},
+		{"0x01", big.NewInt(1)},
+		{"0xf", big.NewInt(15)},
+		{"0x0f", big.NewInt(15)},
+		{"0x10", big.NewInt(16)},
+		{"0xff", big.NewInt(255)},
+		{"0x50429", big.NewInt(328745)},
+		{"0x050429", big.NewInt(328745)},
+	}
+
+	for _, test := range tests {
+		res := MustHexToBigInt(test.in)
+		require.Equal(t, test.out, res)
+	}
+}
+
+func TestMustHexToBigIntPanic(t *testing.T) {
+	assert.Panics(t, func() { MustHexToBigInt("1") }, "should panic for string len < 2")
+	assert.Panics(t, func() { MustHexToBigInt("12") }, "should panic for string not starting with 0x")
+	assert.Panics(t, func() { MustHexToBigInt("0xzz") }, "should panic for string not containing hex characters")
+}