github.com/pingcap/tidb/parser@v0.0.0-20231013125129-93a834a6bf8d/charset/encoding_ascii.go (about)

     1  // Copyright 2021 PingCAP, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package charset
    15  
    16  import (
    17  	"bytes"
    18  	go_unicode "unicode"
    19  
    20  	"golang.org/x/text/encoding"
    21  )
    22  
    23  // EncodingASCIIImpl is the instance of encodingASCII
    24  var EncodingASCIIImpl = &encodingASCII{encodingBase{enc: encoding.Nop}}
    25  
    26  func init() {
    27  	EncodingASCIIImpl.self = EncodingASCIIImpl
    28  }
    29  
    30  // encodingASCII is the ASCII encoding.
    31  type encodingASCII struct {
    32  	encodingBase
    33  }
    34  
    35  // Name implements Encoding interface.
    36  func (*encodingASCII) Name() string {
    37  	return CharsetASCII
    38  }
    39  
    40  // Tp implements Encoding interface.
    41  func (*encodingASCII) Tp() EncodingTp {
    42  	return EncodingTpASCII
    43  }
    44  
    45  // Peek implements Encoding interface.
    46  func (*encodingASCII) Peek(src []byte) []byte {
    47  	if len(src) == 0 {
    48  		return src
    49  	}
    50  	return src[:1]
    51  }
    52  
    53  // IsValid implements Encoding interface.
    54  func (*encodingASCII) IsValid(src []byte) bool {
    55  	srcLen := len(src)
    56  	for i := 0; i < srcLen; i++ {
    57  		if src[i] > go_unicode.MaxASCII {
    58  			return false
    59  		}
    60  	}
    61  	return true
    62  }
    63  
    64  // Transform implements Encoding interface.
    65  func (e *encodingASCII) Transform(dest *bytes.Buffer, src []byte, op Op) ([]byte, error) {
    66  	if e.IsValid(src) {
    67  		return src, nil
    68  	}
    69  	return e.encodingBase.Transform(dest, src, op)
    70  }
    71  
    72  // Foreach implements Encoding interface.
    73  func (*encodingASCII) Foreach(src []byte, _ Op, fn func(from, to []byte, ok bool) bool) {
    74  	for i, w := 0, 0; i < len(src); i += w {
    75  		w = 1
    76  		ok := true
    77  		if src[i] > go_unicode.MaxASCII {
    78  			w = len(EncodingUTF8Impl.Peek(src[i:]))
    79  			ok = false
    80  		}
    81  		if !fn(src[i:i+w], src[i:i+w], ok) {
    82  			return
    83  		}
    84  	}
    85  }