1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Package ioutil implements some I/O utility functions. 6 package ioutil 7 8 import ( 9 "bytes" 10 "io" 11 "os" 12 "sort" 13 "sync" 14 ) 15 16 // readAll reads from r until an error or EOF and returns the data it read 17 // from the internal buffer allocated with a specified capacity. 18 func readAll(r io.Reader, capacity int64) (b []byte, err error) { 19 var buf bytes.Buffer 20 // If the buffer overflows, we will get bytes.ErrTooLarge. 21 // Return that as an error. Any other panic remains. 22 defer func() { 23 e := recover() 24 if e == nil { 25 return 26 } 27 if panicErr, ok := e.(error); ok && panicErr == bytes.ErrTooLarge { 28 err = panicErr 29 } else { 30 panic(e) 31 } 32 }() 33 if int64(int(capacity)) == capacity { 34 buf.Grow(int(capacity)) 35 } 36 _, err = buf.ReadFrom(r) 37 return buf.Bytes(), err 38 } 39 40 // ReadAll reads from r until an error or EOF and returns the data it read. 41 // A successful call returns err == nil, not err == EOF. Because ReadAll is 42 // defined to read from src until EOF, it does not treat an EOF from Read 43 // as an error to be reported. 44 func ReadAll(r io.Reader) ([]byte, error) { 45 return readAll(r, bytes.MinRead) 46 } 47 48 // ReadFile reads the file named by filename and returns the contents. 49 // A successful call returns err == nil, not err == EOF. Because ReadFile 50 // reads the whole file, it does not treat an EOF from Read as an error 51 // to be reported. 52 func ReadFile(filename string) ([]byte, error) { 53 f, err := os.Open(filename) 54 if err != nil { 55 return nil, err 56 } 57 defer f.Close() 58 // It's a good but not certain bet that FileInfo will tell us exactly how much to 59 // read, so let's try it but be prepared for the answer to be wrong. 60 var n int64 = bytes.MinRead 61 62 if fi, err := f.Stat(); err == nil { 63 // As initial capacity for readAll, use Size + a little extra in case Size 64 // is zero, and to avoid another allocation after Read has filled the 65 // buffer. The readAll call will read into its allocated internal buffer 66 // cheaply. If the size was wrong, we'll either waste some space off the end 67 // or reallocate as needed, but in the overwhelmingly common case we'll get 68 // it just right. 69 if size := fi.Size() + bytes.MinRead; size > n { 70 n = size 71 } 72 } 73 return readAll(f, n) 74 } 75 76 // WriteFile writes data to a file named by filename. 77 // If the file does not exist, WriteFile creates it with permissions perm; 78 // otherwise WriteFile truncates it before writing. 79 func WriteFile(filename string, data []byte, perm os.FileMode) error { 80 f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm) 81 if err != nil { 82 return err 83 } 84 n, err := f.Write(data) 85 if err == nil && n < len(data) { 86 err = io.ErrShortWrite 87 } 88 if err1 := f.Close(); err == nil { 89 err = err1 90 } 91 return err 92 } 93 94 // ReadDir reads the directory named by dirname and returns 95 // a list of directory entries sorted by filename. 96 func ReadDir(dirname string) ([]os.FileInfo, error) { 97 f, err := os.Open(dirname) 98 if err != nil { 99 return nil, err 100 } 101 list, err := f.Readdir(-1) 102 f.Close() 103 if err != nil { 104 return nil, err 105 } 106 sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() }) 107 return list, nil 108 } 109 110 type nopCloser struct { 111 io.Reader 112 } 113 114 func (nopCloser) Close() error { return nil } 115 116 // NopCloser returns a ReadCloser with a no-op Close method wrapping 117 // the provided Reader r. 118 func NopCloser(r io.Reader) io.ReadCloser { 119 return nopCloser{r} 120 } 121 122 type devNull int 123 124 // devNull implements ReaderFrom as an optimization so io.Copy to 125 // ioutil.Discard can avoid doing unnecessary work. 126 var _ io.ReaderFrom = devNull(0) 127 128 func (devNull) Write(p []byte) (int, error) { 129 return len(p), nil 130 } 131 132 func (devNull) WriteString(s string) (int, error) { 133 return len(s), nil 134 } 135 136 var blackHolePool = sync.Pool{ 137 New: func() interface{} { 138 b := make([]byte, 8192) 139 return &b 140 }, 141 } 142 143 func (devNull) ReadFrom(r io.Reader) (n int64, err error) { 144 bufp := blackHolePool.Get().(*[]byte) 145 readSize := 0 146 for { 147 readSize, err = r.Read(*bufp) 148 n += int64(readSize) 149 if err != nil { 150 blackHolePool.Put(bufp) 151 if err == io.EOF { 152 return n, nil 153 } 154 return 155 } 156 } 157 } 158 159 // Discard is an io.Writer on which all Write calls succeed 160 // without doing anything. 161 var Discard io.Writer = devNull(0) 162
