Add NullString

Changes EncodeText interface to work for null values in SQL interpolation
and in prepared statements text format.

values.go

@@ -30,6 +30,12 @@ const (
 	BinaryFormatCode = 1
 )
 
+const (
+	NullText   = iota
+	SafeText   = iota
+	UnsafeText = iota
+)
+
 type SerializationError string
 
 func (e SerializationError) Error() string {
@@ -48,9 +54,10 @@ type Scanner interface {
 // queries and for prepared queries when the type does not implement
 // BinaryEncoder
 type TextEncoder interface {
-	// EncodeText MUST sanitize (and quote, if necessary) the returned string.
-	// It will be interpolated directly into the SQL string.
-	EncodeText() (string, error)
+	// EncodeText returns the value encoded into a string. status must be
+	// NullText if the value is NULL, UnsafeText if the value should be quoted
+	// and escaped, or SafeText if the value should not be quoted.
+	EncodeText() (val string, status byte, err error)
 }
 
 // BinaryEncoder is an interface used to encode values in binary format for
@@ -81,11 +88,11 @@ func (n *NullFloat32) Scan(rows *Rows, fd *FieldDescription, size int32) error {
 	return rows.Err()
 }
 
-func (n NullFloat32) EncodeText() (string, error) {
+func (n NullFloat32) EncodeText() (string, byte, error) {
 	if n.Valid {
-		return strconv.FormatFloat(float64(n.Float32), 'f', -1, 32), nil
+		return strconv.FormatFloat(float64(n.Float32), 'f', -1, 32), SafeText, nil
 	} else {
-		return "null", nil
+		return "", NullText, nil
 	}
 }
 
@@ -119,11 +126,11 @@ func (n *NullFloat64) Scan(rows *Rows, fd *FieldDescription, size int32) error {
 	return rows.Err()
 }
 
-func (n NullFloat64) EncodeText() (string, error) {
+func (n NullFloat64) EncodeText() (string, byte, error) {
 	if n.Valid {
-		return strconv.FormatFloat(n.Float64, 'f', -1, 64), nil
+		return strconv.FormatFloat(n.Float64, 'f', -1, 64), SafeText, nil
 	} else {
-		return "null", nil
+		return "", NullText, nil
 	}
 }
 
@@ -136,6 +143,35 @@ func (n NullFloat64) EncodeBinary(w *WriteBuf) error {
 	return encodeFloat8(w, n.Float64)
 }
 
+// NullString represents an integer that may be null. NullString implements
+// the Scanner and TextEncoder interfaces so it may be used both as an
+// argument to Query[Row] and a destination for Scan for prepared and
+// unprepared queries.
+//
+// If Valid is false then the value is NULL.
+type NullString struct {
+	String string
+	Valid  bool // Valid is true if Int64 is not NULL
+}
+
+func (s *NullString) Scan(rows *Rows, fd *FieldDescription, size int32) error {
+	if size == -1 {
+		s.String, s.Valid = "", false
+		return nil
+	}
+	s.Valid = true
+	s.String = decodeText(rows, fd, size)
+	return rows.Err()
+}
+
+func (s NullString) EncodeText() (string, byte, error) {
+	if s.Valid {
+		return s.String, UnsafeText, nil
+	} else {
+		return "", NullText, nil
+	}
+}
+
 // NullInt16 represents an smallint that may be null.
 // NullInt16 implements the Scanner, TextEncoder, and BinaryEncoder interfaces
 // so it may be used both as an argument to Query[Row] and a destination for
@@ -157,11 +193,11 @@ func (n *NullInt16) Scan(rows *Rows, fd *FieldDescription, size int32) error {
 	return rows.Err()
 }
 
-func (n NullInt16) EncodeText() (string, error) {
+func (n NullInt16) EncodeText() (string, byte, error) {
 	if n.Valid {
-		return strconv.FormatInt(int64(n.Int16), 10), nil
+		return strconv.FormatInt(int64(n.Int16), 10), SafeText, nil
 	} else {
-		return "null", nil
+		return "", NullText, nil
 	}
 }
 
@@ -174,7 +210,7 @@ func (n NullInt16) EncodeBinary(w *WriteBuf) error {
 	return encodeInt2(w, n.Int16)
 }
 
-// NullInt32 represents an integer that may be null.
+// NullInt32 represents an smallint that may be null.
 // NullInt32 implements the Scanner, TextEncoder, and BinaryEncoder interfaces
 // so it may be used both as an argument to Query[Row] and a destination for
 // Scan for prepared and unprepared queries.
@@ -195,11 +231,11 @@ func (n *NullInt32) Scan(rows *Rows, fd *FieldDescription, size int32) error {
 	return rows.Err()
 }
 
-func (n NullInt32) EncodeText() (string, error) {
+func (n NullInt32) EncodeText() (string, byte, error) {
 	if n.Valid {
-		return strconv.FormatInt(int64(n.Int32), 10), nil
+		return strconv.FormatInt(int64(n.Int32), 10), SafeText, nil
 	} else {
-		return "null", nil
+		return "", NullText, nil
 	}
 }
 
@@ -233,11 +269,11 @@ func (n *NullInt64) Scan(rows *Rows, fd *FieldDescription, size int32) error {
 	return rows.Err()
 }
 
-func (n NullInt64) EncodeText() (string, error) {
+func (n NullInt64) EncodeText() (string, byte, error) {
 	if n.Valid {
-		return strconv.FormatInt(int64(n.Int64), 10), nil
+		return strconv.FormatInt(int64(n.Int64), 10), SafeText, nil
 	} else {
-		return "null", nil
+		return "", NullText, nil
 	}
 }
 
@@ -327,7 +363,17 @@ func sanitizeArg(arg interface{}) (string, error) {
 	case nil:
 		return "null", nil
 	case TextEncoder:
-		return arg.EncodeText()
+		s, status, err := arg.EncodeText()
+		switch status {
+		case NullText:
+			return "null", err
+		case UnsafeText:
+			return QuoteString(s), err
+		case SafeText:
+			return s, err
+		default:
+			return "", SerializationError("Received invalid status from EncodeText")
+		}
 	default:
 		return "", SerializationError(fmt.Sprintf("%T is not a core type and it does not implement TextEncoder", arg))
 	}