The Go Programming Language

Source file src/pkg/os/file_unix.go

     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 os
     6	
     7	import (
     8		"runtime"
     9		"syscall"
    10	)
    11	
    12	// File represents an open file descriptor.
    13	type File struct {
    14		fd      int
    15		name    string
    16		dirinfo *dirInfo // nil unless directory being read
    17		nepipe  int      // number of consecutive EPIPE in Write
    18	}
    19	
    20	// Fd returns the integer Unix file descriptor referencing the open file.
    21	func (file *File) Fd() int {
    22		if file == nil {
    23			return -1
    24		}
    25		return file.fd
    26	}
    27	
    28	// NewFile returns a new File with the given file descriptor and name.
    29	func NewFile(fd int, name string) *File {
    30		if fd < 0 {
    31			return nil
    32		}
    33		f := &File{fd: fd, name: name}
    34		runtime.SetFinalizer(f, (*File).Close)
    35		return f
    36	}
    37	
    38	// Auxiliary information if the File describes a directory
    39	type dirInfo struct {
    40		buf  []byte // buffer for directory I/O
    41		nbuf int    // length of buf; return value from Getdirentries
    42		bufp int    // location of next record in buf.
    43	}
    44	
    45	// DevNull is the name of the operating system's ``null device.''
    46	// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
    47	const DevNull = "/dev/null"
    48	
    49	// OpenFile is the generalized open call; most users will use Open
    50	// or Create instead.  It opens the named file with specified flag
    51	// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
    52	// methods on the returned File can be used for I/O.
    53	// It returns the File and an Error, if any.
    54	func OpenFile(name string, flag int, perm uint32) (file *File, err Error) {
    55		r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, perm)
    56		if e != 0 {
    57			return nil, &PathError{"open", name, Errno(e)}
    58		}
    59	
    60		// There's a race here with fork/exec, which we are
    61		// content to live with.  See ../syscall/exec.go
    62		if syscall.O_CLOEXEC == 0 { // O_CLOEXEC not supported
    63			syscall.CloseOnExec(r)
    64		}
    65	
    66		return NewFile(r, name), nil
    67	}
    68	
    69	// Close closes the File, rendering it unusable for I/O.
    70	// It returns an Error, if any.
    71	func (file *File) Close() Error {
    72		if file == nil || file.fd < 0 {
    73			return EINVAL
    74		}
    75		var err Error
    76		if e := syscall.Close(file.fd); e != 0 {
    77			err = &PathError{"close", file.name, Errno(e)}
    78		}
    79		file.fd = -1 // so it can't be closed again
    80	
    81		// no need for a finalizer anymore
    82		runtime.SetFinalizer(file, nil)
    83		return err
    84	}
    85	
    86	// Stat returns the FileInfo structure describing file.
    87	// It returns the FileInfo and an error, if any.
    88	func (file *File) Stat() (fi *FileInfo, err Error) {
    89		var stat syscall.Stat_t
    90		e := syscall.Fstat(file.fd, &stat)
    91		if e != 0 {
    92			return nil, &PathError{"stat", file.name, Errno(e)}
    93		}
    94		return fileInfoFromStat(file.name, new(FileInfo), &stat, &stat), nil
    95	}
    96	
    97	// Readdir reads the contents of the directory associated with file and
    98	// returns an array of up to n FileInfo structures, as would be returned
    99	// by Lstat, in directory order. Subsequent calls on the same file will yield
   100	// further FileInfos.
   101	//
   102	// If n > 0, Readdir returns at most n FileInfo structures. In this case, if
   103	// Readdir returns an empty slice, it will return a non-nil error
   104	// explaining why. At the end of a directory, the error is os.EOF.
   105	//
   106	// If n <= 0, Readdir returns all the FileInfo from the directory in
   107	// a single slice. In this case, if Readdir succeeds (reads all
   108	// the way to the end of the directory), it returns the slice and a
   109	// nil os.Error. If it encounters an error before the end of the
   110	// directory, Readdir returns the FileInfo read until that point
   111	// and a non-nil error.
   112	func (file *File) Readdir(n int) (fi []FileInfo, err Error) {
   113		dirname := file.name
   114		if dirname == "" {
   115			dirname = "."
   116		}
   117		dirname += "/"
   118		names, err := file.Readdirnames(n)
   119		fi = make([]FileInfo, len(names))
   120		for i, filename := range names {
   121			fip, err := Lstat(dirname + filename)
   122			if fip == nil || err != nil {
   123				fi[i].Name = filename // rest is already zeroed out
   124			} else {
   125				fi[i] = *fip
   126			}
   127		}
   128		return
   129	}
   130	
   131	// read reads up to len(b) bytes from the File.
   132	// It returns the number of bytes read and an error, if any.
   133	func (f *File) read(b []byte) (n int, err int) {
   134		return syscall.Read(f.fd, b)
   135	}
   136	
   137	// pread reads len(b) bytes from the File starting at byte offset off.
   138	// It returns the number of bytes read and the error, if any.
   139	// EOF is signaled by a zero count with err set to 0.
   140	func (f *File) pread(b []byte, off int64) (n int, err int) {
   141		return syscall.Pread(f.fd, b, off)
   142	}
   143	
   144	// write writes len(b) bytes to the File.
   145	// It returns the number of bytes written and an error, if any.
   146	func (f *File) write(b []byte) (n int, err int) {
   147		return syscall.Write(f.fd, b)
   148	}
   149	
   150	// pwrite writes len(b) bytes to the File starting at byte offset off.
   151	// It returns the number of bytes written and an error, if any.
   152	func (f *File) pwrite(b []byte, off int64) (n int, err int) {
   153		return syscall.Pwrite(f.fd, b, off)
   154	}
   155	
   156	// seek sets the offset for the next Read or Write on file to offset, interpreted
   157	// according to whence: 0 means relative to the origin of the file, 1 means
   158	// relative to the current offset, and 2 means relative to the end.
   159	// It returns the new offset and an error, if any.
   160	func (f *File) seek(offset int64, whence int) (ret int64, err int) {
   161		return syscall.Seek(f.fd, offset, whence)
   162	}
   163	
   164	// Truncate changes the size of the named file.
   165	// If the file is a symbolic link, it changes the size of the link's target.
   166	func Truncate(name string, size int64) Error {
   167		if e := syscall.Truncate(name, size); e != 0 {
   168			return &PathError{"truncate", name, Errno(e)}
   169		}
   170		return nil
   171	}
   172	
   173	// basename removes trailing slashes and the leading directory name from path name
   174	func basename(name string) string {
   175		i := len(name) - 1
   176		// Remove trailing slashes
   177		for ; i > 0 && name[i] == '/'; i-- {
   178			name = name[:i]
   179		}
   180		// Remove leading directory name
   181		for i--; i >= 0; i-- {
   182			if name[i] == '/' {
   183				name = name[i+1:]
   184				break
   185			}
   186		}
   187	
   188		return name
   189	}
   190	
   191	// Pipe returns a connected pair of Files; reads from r return bytes written to w.
   192	// It returns the files and an Error, if any.
   193	func Pipe() (r *File, w *File, err Error) {
   194		var p [2]int
   195	
   196		// See ../syscall/exec.go for description of lock.
   197		syscall.ForkLock.RLock()
   198		e := syscall.Pipe(p[0:])
   199		if iserror(e) {
   200			syscall.ForkLock.RUnlock()
   201			return nil, nil, NewSyscallError("pipe", e)
   202		}
   203		syscall.CloseOnExec(p[0])
   204		syscall.CloseOnExec(p[1])
   205		syscall.ForkLock.RUnlock()
   206	
   207		return NewFile(p[0], "|0"), NewFile(p[1], "|1"), nil
   208	}

release.r60.3. Except as noted, this content is licensed under a Creative Commons Attribution 3.0 License.