fix(spanner): invalid numeric should throw an error

spanner/value.go

@@ -24,6 +24,7 @@ import (
 	"math/big"
 	"reflect"
 	"strconv"
+	"strings"
 	"time"
 
 	"cloud.google.com/go/civil"
@@ -49,13 +50,56 @@ const (
 	NumericScaleDigits = 9
 )
 
+// LossOfPrecisionHandlingOption describes the option to deal with loss of
+// precision on numeric values.
+type LossOfPrecisionHandlingOption int
+
+const (
+	// NumericRound automatically rounds a numeric value that has a higher
+	// precision than what is supported by Spanner, e.g., 0.1234567895 rounds
+	// to 0.123456790.
+	NumericRound LossOfPrecisionHandlingOption = iota
+	// NumericError returns an error for numeric values that have a higher
+	// precision than what is supported by Spanner. E.g. the client returns an
+	// error if the application tries to insert the value 0.1234567895.
+	NumericError
+)
+
+// LossOfPrecisionHandling configures how to deal with loss of precision on
+// numeric values. The value of this configuration is global and will be used
+// for all Spanner clients.
+var LossOfPrecisionHandling LossOfPrecisionHandlingOption
+
 // NumericString returns a string representing a *big.Rat in a format compatible
 // with Spanner SQL. It returns a floating-point literal with 9 digits after the
 // decimal point.
 func NumericString(r *big.Rat) string {
 	return r.FloatString(NumericScaleDigits)
 }
 
+// validateNumeric returns nil if there are no errors. It will return an error
+// when the numeric number is not valid.
+func validateNumeric(r *big.Rat) error {
+	if r == nil {
+		return nil
+	}
+	// Add one more digit to the scale component to find out if there are more
+	// digits than required.
+	strRep := r.FloatString(NumericScaleDigits + 1)
+	strRep = strings.TrimRight(strRep, "0")
+	strRep = strings.TrimLeft(strRep, "-")
+	s := strings.Split(strRep, ".")
+	whole := s[0]
+	scale := s[1]
+	if len(scale) > NumericScaleDigits {
+		return fmt.Errorf("max scale for a numeric is %d. The requested numeric has more", NumericScaleDigits)
+	}
+	if len(whole) > NumericPrecisionDigits-NumericScaleDigits {
+		return fmt.Errorf("max precision for the whole component of a numeric is %d. The requested numeric has a whole component with precision %d", NumericPrecisionDigits-NumericScaleDigits, len(whole))
+	}
+	return nil
+}
+
 var (
 	// CommitTimestamp is a special value used to tell Cloud Spanner to insert
 	// the commit timestamp of the transaction into a column. It can be used in
@@ -2653,6 +2697,15 @@ func encodeValue(v interface{}) (*proto3.Value, *sppb.Type, error) {
 		}
 		pt = listType(floatType())
 	case big.Rat:
+		switch LossOfPrecisionHandling {
+		case NumericError:
+			err = validateNumeric(&v)
+			if err != nil {
+				return nil, nil, err
+			}
+		case NumericRound:
+			// pass
+		}
 		pb.Kind = stringKind(NumericString(&v))
 		pt = numericType()
 	case []big.Rat:
@@ -2677,6 +2730,15 @@ func encodeValue(v interface{}) (*proto3.Value, *sppb.Type, error) {
 		}
 		pt = listType(numericType())
 	case *big.Rat:
+		switch LossOfPrecisionHandling {
+		case NumericError:
+			err = validateNumeric(v)
+			if err != nil {
+				return nil, nil, err
+			}
+		case NumericRound:
+			// pass
+		}
 		if v != nil {
 			pb.Kind = stringKind(NumericString(v))
 		}

spanner/value_test.go

@@ -213,6 +213,8 @@ func TestEncodeValue(t *testing.T) {
 	numValuePtr := big.NewRat(12345, 1e3)
 	var numNilPtr *big.Rat
 	num2ValuePtr := big.NewRat(12345, 1e4)
+	maxNumValuePtr, _ := (&big.Rat{}).SetString("99999999999999999999999999999.999999999")
+	minNumValuePtr, _ := (&big.Rat{}).SetString("-99999999999999999999999999999.999999999")
 
 	var (
 		tString  = stringType()
@@ -281,6 +283,8 @@ func TestEncodeValue(t *testing.T) {
 		// NUMERIC / NUMERIC ARRAY
 		{*numValuePtr, numericProto(numValuePtr), tNumeric, "big.Rat"},
 		{numValuePtr, numericProto(numValuePtr), tNumeric, "*big.Rat"},
+		{maxNumValuePtr, numericProto(maxNumValuePtr), tNumeric, "max numeric"},
+		{minNumValuePtr, numericProto(minNumValuePtr), tNumeric, "min numeric"},
 		{numNilPtr, nullProto(), tNumeric, "*big.Rat with null"},
 		{NullNumeric{*numValuePtr, true}, numericProto(numValuePtr), tNumeric, "NullNumeric with value"},
 		{NullNumeric{*numValuePtr, false}, nullProto(), tNumeric, "NullNumeric with null"},
@@ -406,6 +410,40 @@ func TestEncodeValue(t *testing.T) {
 	}
 }
 
+// Test encoding invalid values.
+func TestEncodeInvalidValues(t *testing.T) {
+	type CustomNumeric big.Rat
+
+	invalidNumPtr1 := big.NewRat(11234567891, 1e10)
+	invalidNumPtr2, _ := (&big.Rat{}).SetString("199999999999999999999999999999.999999999")
+
+	// Enable error mode.
+	LossOfPrecisionHandling = NumericError
+
+	for i, test := range []struct {
+		desc   string
+		in     interface{}
+		errMsg string
+	}{
+		// NUMERIC
+		{desc: "numeric pointer with invalid scale component", in: invalidNumPtr1, errMsg: "max scale for a numeric is 9. The requested numeric has more"},
+		{desc: "numeric pointer with invalid whole component", in: invalidNumPtr2, errMsg: "max precision for the whole component of a numeric is 29. The requested numeric has a whole component with precision 30"},
+		{desc: "numeric with invalid scale component", in: *invalidNumPtr1, errMsg: "max scale for a numeric is 9. The requested numeric has more"},
+		{desc: "numeric with invalid whole component", in: *invalidNumPtr2, errMsg: "max precision for the whole component of a numeric is 29. The requested numeric has a whole component with precision 30"},
+		// CUSTOM NUMERIC
+		{desc: "custom numeric type with invalid scale component", in: CustomNumeric(*invalidNumPtr1), errMsg: "max scale for a numeric is 9. The requested numeric has more"},
+		{desc: "custom numeric type with invalid whole component", in: CustomNumeric(*invalidNumPtr2), errMsg: "max precision for the whole component of a numeric is 29. The requested numeric has a whole component with precision 30"},
+	} {
+		_, _, err := encodeValue(test.in)
+		if err == nil {
+			t.Fatalf("#%d (%s): want error during encoding, but got nil", i, test.desc)
+		}
+		if err.Error() != test.errMsg {
+			t.Errorf("#%d (%s): incorrect error message, got %v, want %v", i, test.desc, err, test.errMsg)
+		}
+	}
+}
+
 type encodeTest struct {
 	desc     string
 	in       interface{}