conversion: fix unmarshalling overflow (holiman#185)

The json-unmarshalling from decimal form inorrectly invoked fromDecimal,
instead of SetFromDecimal. The former assumes that the input has already
been validated, and thus does not throw errors on overflow.

Closes holiman#184

conversion.go

@@ -236,7 +236,7 @@ func (z *Int) UnmarshalText(input []byte) error {
 	if len(input) >= 2 && input[0] == '0' && (input[1] == 'x' || input[1] == 'X') {
 		return z.fromHex(string(input))
 	}
-	return z.fromDecimal(string(input))
+	return z.SetFromDecimal(string(input))
 }
 
 // SetFromBig converts a big.Int to Int and sets the value to z.
@@ -712,7 +712,7 @@ func (z *Int) MarshalJSON() ([]byte, error) {
 func (z *Int) UnmarshalJSON(input []byte) error {
 	if len(input) < 2 || input[0] != '"' || input[len(input)-1] != '"' {
 		// if not quoted, it must be decimal
-		return z.fromDecimal(string(input))
+		return z.SetFromDecimal(string(input))
 	}
 	return z.UnmarshalText(input[1 : len(input)-1])
 }

conversion_test.go

@@ -1405,6 +1405,34 @@ func TestEnDecode(t *testing.T) {
 	}
 }
 
+func TestMarshallingErrors(t *testing.T) {
+	var check = func(repr string) string {
+		a := new(Int)
+		if err := json.Unmarshal([]byte(repr), a); err != nil {
+			return fmt.Sprintf("error: %v", err.Error())
+		}
+		return a.String()
+	}
+
+	for i, tc := range []string{
+		`0x1000000000000000000000000000000000000000000000000000000000000000`,
+		`0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff`,
+		`0x10000000000000000000000000000000000000000000000000000000000000000`,
+		`0x10000000000000000000000000000000000000000000000000000000000000001`,
+		`0x111110000000000000000000000000000000000000000000000000000000000000001`,
+	} {
+		reference, ok := new(big.Int).SetString(tc, 0)
+		if !ok {
+			t.Fatalf("test %d: not ok input %q", i, tc)
+		}
+		haveHex := check(fmt.Sprintf(`"%#x"`, reference))
+		haveDec := check(fmt.Sprintf(`"%#d"`, reference))
+		if haveHex != haveDec {
+			t.Fatalf("test %d: hex unmarshal != dec unmarshal, \nhex -> %q\ndec -> %q\n", i, haveHex, haveDec)
+		}
+	}
+}
+
 func TestNil(t *testing.T) {
 	a := NewInt(1337)
 	if err := a.Scan(nil); err != nil {

decimal.go

@@ -177,6 +177,8 @@ var multipliers = [5]*Int{
 // fromDecimal is a helper function to only ever be called via SetFromDecimal
 // this function takes a string and chunks it up, calling ParseUint on it up to 5 times
 // these chunks are then multiplied by the proper power of 10, then added together.
+// Note: this method assumes that some basic validity-checks have already been performed
+// on the input 'bs'. See SetFromDecimal.
 func (z *Int) fromDecimal(bs string) error {
 	// first clear the input
 	z.Clear()