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length.go
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length.go
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// Copyright 2020-2021 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package function
import (
"fmt"
"unicode/utf8"
"github.com/gabereiser/go-mysql-server/sql/encodings"
"github.com/gabereiser/go-mysql-server/sql/types"
"github.com/gabereiser/go-mysql-server/sql"
"github.com/gabereiser/go-mysql-server/sql/expression"
)
// Length returns the length of a string or binary content, either in bytes
// or characters.
type Length struct {
expression.UnaryExpression
CountType CountType
}
var _ sql.FunctionExpression = (*Length)(nil)
// CountType is the kind of length count.
type CountType bool
const (
// NumBytes counts the number of bytes in a string or binary content.
NumBytes = CountType(false)
// NumChars counts the number of characters in a string or binary content.
NumChars = CountType(true)
)
// NewLength returns a new LENGTH function.
func NewLength(e sql.Expression) sql.Expression {
return &Length{expression.UnaryExpression{Child: e}, NumBytes}
}
// NewCharLength returns a new CHAR_LENGTH function.
func NewCharLength(e sql.Expression) sql.Expression {
return &Length{expression.UnaryExpression{Child: e}, NumChars}
}
// FunctionName implements sql.FunctionExpression
func (l *Length) FunctionName() string {
if l.CountType == NumChars {
return "character_length"
} else if l.CountType == NumBytes {
return "length"
} else {
panic("unknown name for length count type")
}
}
// Description implements sql.FunctionExpression
func (l *Length) Description() string {
if l.CountType == NumChars {
return "returns the length of the string in characters."
} else if l.CountType == NumBytes {
return "returns the length of the string in bytes."
} else {
panic("unknown description for length count type")
}
}
// WithChildren implements the Expression interface.
func (l *Length) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 1 {
return nil, sql.ErrInvalidChildrenNumber.New(l, len(children), 1)
}
return &Length{expression.UnaryExpression{Child: children[0]}, l.CountType}, nil
}
// Type implements the sql.Expression interface.
func (l *Length) Type() sql.Type { return types.Int32 }
func (l *Length) String() string {
if l.CountType == NumBytes {
return fmt.Sprintf("length(%s)", l.Child)
}
return fmt.Sprintf("char_length(%s)", l.Child)
}
func (l *Length) DebugString() string {
if l.CountType == NumBytes {
return fmt.Sprintf("length(%s)", sql.DebugString(l.Child))
}
return fmt.Sprintf("char_length(%s)", sql.DebugString(l.Child))
}
// Eval implements the sql.Expression interface.
func (l *Length) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
val, err := l.Child.Eval(ctx, row)
if err != nil {
return nil, err
}
if val == nil {
return nil, nil
}
content, collation, err := types.ConvertToCollatedString(val, l.Child.Type())
if err != nil {
return nil, err
}
charSetEncoder := collation.CharacterSet().Encoder()
if l.CountType == NumBytes {
encodedContent, ok := charSetEncoder.Encode(encodings.StringToBytes(content))
if !ok {
return nil, fmt.Errorf("unable to re-encode string for LENGTH function")
}
return int32(len(encodedContent)), nil
} else {
contentLen := int32(0)
for len(content) > 0 {
cr, cRead := charSetEncoder.NextRune(content)
if cRead == 0 || cr == utf8.RuneError {
return 0, sql.ErrCollationMalformedString.New("checking length")
}
content = content[cRead:]
contentLen++
}
return contentLen, nil
}
}