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 buf := bytes.NewBuffer(make([]byte, 0, capacity)) 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 _, err = buf.ReadFrom(r) 34 return buf.Bytes(), err 35 } 36 37 // ReadAll reads from r until an error or EOF and returns the data it read. 38 // A successful call returns err == nil, not err == EOF. Because ReadAll is 39 // defined to read from src until EOF, it does not treat an EOF from Read 40 // as an error to be reported. 41 func ReadAll(r io.Reader) ([]byte, error) { 42 return readAll(r, bytes.MinRead) 43 } 44 45 // ReadFile reads the file named by filename and returns the contents. 46 // A successful call returns err == nil, not err == EOF. Because ReadFile 47 // reads the whole file, it does not treat an EOF from Read as an error 48 // to be reported. 49 func ReadFile(filename string) ([]byte, error) { 50 f, err := os.Open(filename) 51 if err != nil { 52 return nil, err 53 } 54 defer f.Close() 55 // It's a good but not certain bet that FileInfo will tell us exactly how much to 56 // read, so let's try it but be prepared for the answer to be wrong. 57 var n int64 58 59 if fi, err := f.Stat(); err == nil { 60 // Don't preallocate a huge buffer, just in case. 61 if size := fi.Size(); size < 1e9 { 62 n = size 63 } 64 } 65 // As initial capacity for readAll, use n + a little extra in case Size is zero, 66 // and to avoid another allocation after Read has filled the buffer. The readAll 67 // call will read into its allocated internal buffer cheaply. If the size was 68 // wrong, we'll either waste some space off the end or reallocate as needed, but 69 // in the overwhelmingly common case we'll get it just right. 70 return readAll(f, n+bytes.MinRead) 71 } 72 73 // WriteFile writes data to a file named by filename. 74 // If the file does not exist, WriteFile creates it with permissions perm; 75 // otherwise WriteFile truncates it before writing. 76 func WriteFile(filename string, data []byte, perm os.FileMode) error { 77 f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm) 78 if err != nil { 79 return err 80 } 81 n, err := f.Write(data) 82 if err == nil && n < len(data) { 83 err = io.ErrShortWrite 84 } 85 if err1 := f.Close(); err == nil { 86 err = err1 87 } 88 return err 89 } 90 91 // ReadDir reads the directory named by dirname and returns 92 // a list of directory entries sorted by filename. 93 func ReadDir(dirname string) ([]os.FileInfo, error) { 94 f, err := os.Open(dirname) 95 if err != nil { 96 return nil, err 97 } 98 list, err := f.Readdir(-1) 99 f.Close() 100 if err != nil { 101 return nil, err 102 } 103 sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() }) 104 return list, nil 105 } 106 107 type nopCloser struct { 108 io.Reader 109 } 110 111 func (nopCloser) Close() error { return nil } 112 113 // NopCloser returns a ReadCloser with a no-op Close method wrapping 114 // the provided Reader r. 115 func NopCloser(r io.Reader) io.ReadCloser { 116 return nopCloser{r} 117 } 118 119 type devNull int 120 121 // devNull implements ReaderFrom as an optimization so io.Copy to 122 // ioutil.Discard can avoid doing unnecessary work. 123 var _ io.ReaderFrom = devNull(0) 124 125 func (devNull) Write(p []byte) (int, error) { 126 return len(p), nil 127 } 128 129 func (devNull) WriteString(s string) (int, error) { 130 return len(s), nil 131 } 132 133 var blackHolePool = sync.Pool{ 134 New: func() interface{} { 135 b := make([]byte, 8192) 136 return &b 137 }, 138 } 139 140 func (devNull) ReadFrom(r io.Reader) (n int64, err error) { 141 bufp := blackHolePool.Get().(*[]byte) 142 readSize := 0 143 for { 144 readSize, err = r.Read(*bufp) 145 n += int64(readSize) 146 if err != nil { 147 blackHolePool.Put(bufp) 148 if err == io.EOF { 149 return n, nil 150 } 151 return 152 } 153 } 154 } 155 156 // Discard is an io.Writer on which all Write calls succeed 157 // without doing anything. 158 var Discard io.Writer = devNull(0) 159
