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// 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 ioutil implements some I/O utility functions.
package ioutil

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

// readAll reads from r until an error or EOF and returns the data it read
// from the internal buffer allocated with a specified capacity.
func readAll(r io.Reader, capacity int64) (b []byte, err error) {
        buf := bytes.NewBuffer(make([]byte, 0, capacity))
        // If the buffer overflows, we will get bytes.ErrTooLarge.
        // Return that as an error. Any other panic remains.
        defer func() {
                e := recover()
                if e == nil {
                        return
                }
                if panicErr, ok := e.(error); ok && panicErr == bytes.ErrTooLarge {
                        err = panicErr
                } else {
                        panic(e)
                }
        }()
        _, err = buf.ReadFrom(r)
        return buf.Bytes(), err
}

// ReadAll reads from r until an error or EOF and returns the data it read.
// A successful call returns err == nil, not err == EOF. Because ReadAll is
// defined to read from src until EOF, it does not treat an EOF from Read
// as an error to be reported.
func ReadAll(r io.Reader) ([]byte, error) {
        return readAll(r, bytes.MinRead)
}

// ReadFile reads the file named by filename and returns the contents.
// A successful call returns err == nil, not err == EOF. Because ReadFile
// reads the whole file, it does not treat an EOF from Read as an error
// to be reported.
func ReadFile(filename string) ([]byte, error) {
        f, err := os.Open(filename)
        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 size := fi.Size(); err == nil && size < 2e9 { // Don't preallocate a huge buffer, just in case.
                n = size
        }
        // As initial capacity for readAll, use n + a little extra in case Size is zero,
        // and to avoid another allocation after Read has filled the buffer.  The readAll
        // call will read into its allocated internal buffer 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.
        return readAll(f, n+bytes.MinRead)
}

// 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 os.FileMode) error {
        f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|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
}

// byName implements sort.Interface.
type byName []os.FileInfo

func (f byName) Len() int           { return len(f) }
func (f byName) Less(i, j int) bool { return f[i].Name() < f[j].Name() }
func (f byName) 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, error) {
        f, err := os.Open(dirname)
        if err != nil {
                return nil, err
        }
        list, err := f.Readdir(-1)
        f.Close()
        if err != nil {
                return nil, err
        }
        sort.Sort(byName(list))
        return list, nil
}

type nopCloser struct {
        io.Reader
}

func (nopCloser) Close() error { return nil }

// NopCloser returns a ReadCloser with a no-op Close method wrapping
// the provided Reader r.
func NopCloser(r io.Reader) io.ReadCloser {
        return nopCloser{r}
}

type devNull int

// devNull implements ReaderFrom as an optimization so io.Copy to
// ioutil.Discard can avoid doing unnecessary work.
var _ io.ReaderFrom = devNull(0)

func (devNull) Write(p []byte) (int, error) {
        return len(p), nil
}

var blackHole = make([]byte, 8192)

func (devNull) ReadFrom(r io.Reader) (n int64, err error) {
        readSize := 0
        for {
                readSize, err = r.Read(blackHole)
                n += int64(readSize)
                if err != nil {
                        if err == io.EOF {
                                return n, nil
                        }
                        return
                }
        }
        panic("unreachable")
}

// Discard is an io.Writer on which all Write calls succeed
// without doing anything.
var Discard io.Writer = devNull(0)