src/pkg/io/ioutil/ioutil.go

// 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.

// Utility functions.

package ioutil

import (
	"bytes"
	"io"
	"os"
	"sort"
)

// ReadAll reads from r until an error or EOF and returns the data it read.
func ReadAll(r io.Reader) ([]byte, os.Error) {
	var buf bytes.Buffer
	_, err := io.Copy(&buf, r)
	return buf.Bytes(), err
}

// ReadFile reads the file named by filename and returns the contents.
func ReadFile(filename string) ([]byte, os.Error) {
	f, err := os.Open(filename, os.O_RDONLY, 0)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	// It's a good but not certain bet that FileInfo will tell us exactly how much to
	// read, so let's try it but be prepared for the answer to be wrong.
	fi, err := f.Stat()
	var n int64
	if err == nil && fi.Size < 2e9 { // Don't preallocate a huge buffer, just in case.
		n = fi.Size
	}
	// Add a little extra in case Size is zero, and to avoid another allocation after
	// Read has filled the buffer.
	n += bytes.MinRead
	// Pre-allocate the correct size of buffer, then set its size to zero.  The
	// Buffer will read into the allocated space cheaply.  If the size was wrong,
	// we'll either waste some space off the end or reallocate as needed, but
	// in the overwhelmingly common case we'll get it just right.
	buf := bytes.NewBuffer(make([]byte, 0, n))
	_, err = buf.ReadFrom(f)
	return buf.Bytes(), err
}

// WriteFile writes data to a file named by filename.
// If the file does not exist, WriteFile creates it with permissions perm;
// otherwise WriteFile truncates it before writing.
func WriteFile(filename string, data []byte, perm uint32) os.Error {
	f, err := os.Open(filename, os.O_WRONLY|os.O_CREAT|os.O_TRUNC, perm)
	if err != nil {
		return err
	}
	n, err := f.Write(data)
	f.Close()
	if err == nil && n < len(data) {
		err = io.ErrShortWrite
	}
	return err
}

// A dirList implements sort.Interface.
type fileInfoList []*os.FileInfo

func (f fileInfoList) Len() int           { return len(f) }
func (f fileInfoList) Less(i, j int) bool { return f[i].Name < f[j].Name }
func (f fileInfoList) Swap(i, j int)      { f[i], f[j] = f[j], f[i] }

// ReadDir reads the directory named by dirname and returns
// a list of sorted directory entries.
func ReadDir(dirname string) ([]*os.FileInfo, os.Error) {
	f, err := os.Open(dirname, os.O_RDONLY, 0)
	if err != nil {
		return nil, err
	}
	list, err := f.Readdir(-1)
	f.Close()
	if err != nil {
		return nil, err
	}
	fi := make(fileInfoList, len(list))
	for i := range list {
		fi[i] = &list[i]
	}
	sort.Sort(fi)
	return fi, nil
}