1/* 2Copyright 2012 Google Inc. 3 4Licensed under the Apache License, Version 2.0 (the "License"); 5you may not use this file except in compliance with the License. 6You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10Unless required by applicable law or agreed to in writing, software 11distributed under the License is distributed on an "AS IS" BASIS, 12WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13See the License for the specific language governing permissions and 14limitations under the License. 15*/ 16 17package groupcache 18 19import ( 20 "bytes" 21 "errors" 22 "io" 23 "strings" 24) 25 26// A ByteView holds an immutable view of bytes. 27// Internally it wraps either a []byte or a string, 28// but that detail is invisible to callers. 29// 30// A ByteView is meant to be used as a value type, not 31// a pointer (like a time.Time). 32type ByteView struct { 33 // If b is non-nil, b is used, else s is used. 34 b []byte 35 s string 36} 37 38// Len returns the view's length. 39func (v ByteView) Len() int { 40 if v.b != nil { 41 return len(v.b) 42 } 43 return len(v.s) 44} 45 46// ByteSlice returns a copy of the data as a byte slice. 47func (v ByteView) ByteSlice() []byte { 48 if v.b != nil { 49 return cloneBytes(v.b) 50 } 51 return []byte(v.s) 52} 53 54// String returns the data as a string, making a copy if necessary. 55func (v ByteView) String() string { 56 if v.b != nil { 57 return string(v.b) 58 } 59 return v.s 60} 61 62// At returns the byte at index i. 63func (v ByteView) At(i int) byte { 64 if v.b != nil { 65 return v.b[i] 66 } 67 return v.s[i] 68} 69 70// Slice slices the view between the provided from and to indices. 71func (v ByteView) Slice(from, to int) ByteView { 72 if v.b != nil { 73 return ByteView{b: v.b[from:to]} 74 } 75 return ByteView{s: v.s[from:to]} 76} 77 78// SliceFrom slices the view from the provided index until the end. 79func (v ByteView) SliceFrom(from int) ByteView { 80 if v.b != nil { 81 return ByteView{b: v.b[from:]} 82 } 83 return ByteView{s: v.s[from:]} 84} 85 86// Copy copies b into dest and returns the number of bytes copied. 87func (v ByteView) Copy(dest []byte) int { 88 if v.b != nil { 89 return copy(dest, v.b) 90 } 91 return copy(dest, v.s) 92} 93 94// Equal returns whether the bytes in b are the same as the bytes in 95// b2. 96func (v ByteView) Equal(b2 ByteView) bool { 97 if b2.b == nil { 98 return v.EqualString(b2.s) 99 } 100 return v.EqualBytes(b2.b) 101} 102 103// EqualString returns whether the bytes in b are the same as the bytes 104// in s. 105func (v ByteView) EqualString(s string) bool { 106 if v.b == nil { 107 return v.s == s 108 } 109 l := v.Len() 110 if len(s) != l { 111 return false 112 } 113 for i, bi := range v.b { 114 if bi != s[i] { 115 return false 116 } 117 } 118 return true 119} 120 121// EqualBytes returns whether the bytes in b are the same as the bytes 122// in b2. 123func (v ByteView) EqualBytes(b2 []byte) bool { 124 if v.b != nil { 125 return bytes.Equal(v.b, b2) 126 } 127 l := v.Len() 128 if len(b2) != l { 129 return false 130 } 131 for i, bi := range b2 { 132 if bi != v.s[i] { 133 return false 134 } 135 } 136 return true 137} 138 139// Reader returns an io.ReadSeeker for the bytes in v. 140func (v ByteView) Reader() io.ReadSeeker { 141 if v.b != nil { 142 return bytes.NewReader(v.b) 143 } 144 return strings.NewReader(v.s) 145} 146 147// ReadAt implements io.ReaderAt on the bytes in v. 148func (v ByteView) ReadAt(p []byte, off int64) (n int, err error) { 149 if off < 0 { 150 return 0, errors.New("view: invalid offset") 151 } 152 if off >= int64(v.Len()) { 153 return 0, io.EOF 154 } 155 n = v.SliceFrom(int(off)).Copy(p) 156 if n < len(p) { 157 err = io.EOF 158 } 159 return 160} 161 162// WriteTo implements io.WriterTo on the bytes in v. 163func (v ByteView) WriteTo(w io.Writer) (n int64, err error) { 164 var m int 165 if v.b != nil { 166 m, err = w.Write(v.b) 167 } else { 168 m, err = io.WriteString(w, v.s) 169 } 170 if err == nil && m < v.Len() { 171 err = io.ErrShortWrite 172 } 173 n = int64(m) 174 return 175} 176