summaryrefslogtreecommitdiff
path: root/src/pkg/os/file.go
blob: 2dd1fcf282f65affadb340af514252c4bfdf79cc (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package os provides a platform-independent interface to operating system
// functionality. The design is Unix-like, although the error handling is
// Go-like; failing calls return values of type error rather than error numbers.
// Often, more information is available within the error. For example,
// if a call that takes a file name fails, such as Open or Stat, the error
// will include the failing file name when printed and will be of type
// *PathError, which may be unpacked for more information.
//
// The os interface is intended to be uniform across all operating systems.
// Features not generally available appear in the system-specific package syscall.
//
// Here is a simple example, opening a file and reading some of it.
//
//	file, err := os.Open("file.go") // For read access.
//	if err != nil {
//		log.Fatal(err)
//	}
//
// If the open fails, the error string will be self-explanatory, like
//
//	open file.go: no such file or directory
//
// The file's data can then be read into a slice of bytes. Read and
// Write take their byte counts from the length of the argument slice.
//
//	data := make([]byte, 100)
//	count, err := file.Read(data)
//	if err != nil {
//		log.Fatal(err)
//	}
//	fmt.Printf("read %d bytes: %q\n", count, data[:count])
//
package os

import (
	"io"
	"syscall"
)

// Name returns the name of the file as presented to Open.
func (f *File) Name() string { return f.name }

// Stdin, Stdout, and Stderr are open Files pointing to the standard input,
// standard output, and standard error file descriptors.
var (
	Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
	Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
	Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
)

// Flags to Open wrapping those of the underlying system. Not all flags
// may be implemented on a given system.
const (
	O_RDONLY int = syscall.O_RDONLY // open the file read-only.
	O_WRONLY int = syscall.O_WRONLY // open the file write-only.
	O_RDWR   int = syscall.O_RDWR   // open the file read-write.
	O_APPEND int = syscall.O_APPEND // append data to the file when writing.
	O_CREATE int = syscall.O_CREAT  // create a new file if none exists.
	O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist
	O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.
	O_TRUNC  int = syscall.O_TRUNC  // if possible, truncate file when opened.
)

// Seek whence values.
const (
	SEEK_SET int = 0 // seek relative to the origin of the file
	SEEK_CUR int = 1 // seek relative to the current offset
	SEEK_END int = 2 // seek relative to the end
)

// LinkError records an error during a link or symlink or rename
// system call and the paths that caused it.
type LinkError struct {
	Op  string
	Old string
	New string
	Err error
}

func (e *LinkError) Error() string {
	return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error()
}

// Read reads up to len(b) bytes from the File.
// It returns the number of bytes read and an error, if any.
// EOF is signaled by a zero count with err set to io.EOF.
func (f *File) Read(b []byte) (n int, err error) {
	if f == nil {
		return 0, ErrInvalid
	}
	n, e := f.read(b)
	if n < 0 {
		n = 0
	}
	if n == 0 && len(b) > 0 && e == nil {
		return 0, io.EOF
	}
	if e != nil {
		err = &PathError{"read", f.name, e}
	}
	return n, err
}

// ReadAt reads len(b) bytes from the File starting at byte offset off.
// It returns the number of bytes read and the error, if any.
// ReadAt always returns a non-nil error when n < len(b).
// At end of file, that error is io.EOF.
func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
	if f == nil {
		return 0, ErrInvalid
	}
	for len(b) > 0 {
		m, e := f.pread(b, off)
		if m == 0 && e == nil {
			return n, io.EOF
		}
		if e != nil {
			err = &PathError{"read", f.name, e}
			break
		}
		n += m
		b = b[m:]
		off += int64(m)
	}
	return
}

// Write writes len(b) bytes to the File.
// It returns the number of bytes written and an error, if any.
// Write returns a non-nil error when n != len(b).
func (f *File) Write(b []byte) (n int, err error) {
	if f == nil {
		return 0, ErrInvalid
	}
	n, e := f.write(b)
	if n < 0 {
		n = 0
	}

	epipecheck(f, e)

	if e != nil {
		err = &PathError{"write", f.name, e}
	}
	return n, err
}

// WriteAt writes len(b) bytes to the File starting at byte offset off.
// It returns the number of bytes written and an error, if any.
// WriteAt returns a non-nil error when n != len(b).
func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
	if f == nil {
		return 0, ErrInvalid
	}
	for len(b) > 0 {
		m, e := f.pwrite(b, off)
		if e != nil {
			err = &PathError{"write", f.name, e}
			break
		}
		n += m
		b = b[m:]
		off += int64(m)
	}
	return
}

// Seek sets the offset for the next Read or Write on file to offset, interpreted
// according to whence: 0 means relative to the origin of the file, 1 means
// relative to the current offset, and 2 means relative to the end.
// It returns the new offset and an error, if any.
func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
	if f == nil {
		return 0, ErrInvalid
	}
	r, e := f.seek(offset, whence)
	if e == nil && f.dirinfo != nil && r != 0 {
		e = syscall.EISDIR
	}
	if e != nil {
		return 0, &PathError{"seek", f.name, e}
	}
	return r, nil
}

// WriteString is like Write, but writes the contents of string s rather than
// a slice of bytes.
func (f *File) WriteString(s string) (ret int, err error) {
	if f == nil {
		return 0, ErrInvalid
	}
	return f.Write([]byte(s))
}

// Mkdir creates a new directory with the specified name and permission bits.
// If there is an error, it will be of type *PathError.
func Mkdir(name string, perm FileMode) error {
	e := syscall.Mkdir(name, syscallMode(perm))
	if e != nil {
		return &PathError{"mkdir", name, e}
	}
	return nil
}

// Chdir changes the current working directory to the named directory.
// If there is an error, it will be of type *PathError.
func Chdir(dir string) error {
	if e := syscall.Chdir(dir); e != nil {
		return &PathError{"chdir", dir, e}
	}
	return nil
}

// Chdir changes the current working directory to the file,
// which must be a directory.
// If there is an error, it will be of type *PathError.
func (f *File) Chdir() error {
	if f == nil {
		return ErrInvalid
	}
	if e := syscall.Fchdir(f.fd); e != nil {
		return &PathError{"chdir", f.name, e}
	}
	return nil
}

// Open opens the named file for reading.  If successful, methods on
// the returned file can be used for reading; the associated file
// descriptor has mode O_RDONLY.
// If there is an error, it will be of type *PathError.
func Open(name string) (file *File, err error) {
	return OpenFile(name, O_RDONLY, 0)
}

// Create creates the named file mode 0666 (before umask), truncating
// it if it already exists.  If successful, methods on the returned
// File can be used for I/O; the associated file descriptor has mode
// O_RDWR.
// If there is an error, it will be of type *PathError.
func Create(name string) (file *File, err error) {
	return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
}

// lstat is overridden in tests.
var lstat = Lstat