fix shamir share parsing

Author: ppolariss

utils/shamir/shamir.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	. "math/big"
+	"strings"
 
 	"auth_next/utils"
 )
@@ -30,9 +31,17 @@ func (share Share) ToString() string {
 
 func FromString(rawShare string) (Share, error) {
 	share := Share{new(Int), new(Int)}
-	_, err := fmt.Sscanf(rawShare, "%v\n%v", share.X, share.Y)
-	if err != nil {
-		return share, err
+
+	fields := strings.Fields(rawShare)
+	if len(fields) != 2 {
+		return share, fmt.Errorf("invalid share format: expected exactly two decimal integer coordinates, got %d", len(fields))
+	}
+
+	if _, ok := share.X.SetString(fields[0], 10); !ok {
+		return share, errors.New("invalid share x coordinate: expected a decimal integer")
+	}
+	if _, ok := share.Y.SetString(fields[1], 10); !ok {
+		return share, errors.New("invalid share y coordinate: expected a decimal integer")
 	}
 	return share, nil
 }

utils/shamir/shamir_test.go

@@ -3,6 +3,7 @@ package shamir
 import (
 	"fmt"
 	. "math/big"
+	"strings"
 	"testing"
 )
 
@@ -18,6 +19,47 @@ func TestFromString(t *testing.T) {
 	t.Log(share)
 }
 
+func TestFromStringAllowsSurroundingWhitespace(t *testing.T) {
+	share, err := FromString(" \r\n12333333333333333333333333\r\n45666666666666666666666666666\n ")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if share.X.String() != "12333333333333333333333333" {
+		t.Fatalf("unexpected x coordinate: %s", share.X)
+	}
+	if share.Y.String() != "45666666666666666666666666666" {
+		t.Fatalf("unexpected y coordinate: %s", share.Y)
+	}
+}
+
+func TestFromStringRejectsEmptyShare(t *testing.T) {
+	_, err := FromString("")
+	if err == nil {
+		t.Fatal("expected empty share to fail")
+	}
+	if strings.Contains(err.Error(), "number has no digits") {
+		t.Fatalf("expected a clear share format error, got %q", err)
+	}
+}
+
+func TestFromStringRejectsInvalidCoordinate(t *testing.T) {
+	_, err := FromString("123\n")
+	if err == nil {
+		t.Fatal("expected incomplete share to fail")
+	}
+	if !strings.Contains(err.Error(), "expected exactly two decimal integer coordinates") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	_, err = FromString("123\nabc")
+	if err == nil {
+		t.Fatal("expected invalid y coordinate to fail")
+	}
+	if !strings.Contains(err.Error(), "invalid share y coordinate") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 func TestEncryptAndDecrypt(t *testing.T) {
 	secret := "123456"
 	shares, err := Encrypt(secret, 7, 4)