// 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 io provides basic interfaces to I/O primitives.
// Its primary job is to wrap existing implementations of such primitives,
// such as those in package os, into shared public interfaces that
// abstract the functionality, plus some other related primitives.
//
// Because these interfaces and primitives wrap lower-level operations with
// various implementations, unless otherwise informed clients should not
// assume they are safe for parallel execution.
package io
import (
"errors"
)
// Seek whence values.
const (
SeekStart = 0 // seek relative to the origin of the file
SeekCurrent = 1 // seek relative to the current offset
SeekEnd = 2 // seek relative to the end
)
// ErrShortWrite means that a write accepted fewer bytes than requested
// but failed to return an explicit error.
var ErrShortWrite = errors.New("short write")
// ErrShortBuffer means that a read required a longer buffer than was provided.
var ErrShortBuffer = errors.New("short buffer")
// EOF is the error returned by Read when no more input is available.
// Functions should return EOF only to signal a graceful end of input.
// If the EOF occurs unexpectedly in a structured data stream,
// the appropriate error is either ErrUnexpectedEOF or some other error
// giving more detail.
var EOF = errors.New("EOF")
// ErrUnexpectedEOF means that EOF was encountered in the
// middle of reading a fixed-size block or data structure.
var ErrUnexpectedEOF = errors.New("unexpected EOF")
// ErrNoProgress is returned by some clients of an io.Reader when
// many calls to Read have failed to return any data or error,
// usually the sign of a broken io.Reader implementation.
var ErrNoProgress = errors.New("multiple Read calls return no data or error")
// Reader is the interface that wraps the basic Read method.
//
// Read reads up to len(p) bytes into p. It returns the number of bytes
// read (0 <= n <= len(p)) and any error encountered. Even if Read
// returns n < len(p), it may use all of p as scratch space during the call.
// If some data is available but not len(p) bytes, Read conventionally
// returns what is available instead of waiting for more.
//
// When Read encounters an error or end-of-file condition after
// successfully reading n > 0 bytes, it returns the number of
// bytes read. It may return the (non-nil) error from the same call
// or return the error (and n == 0) from a subsequent call.
// An instance of this general case is that a Reader returning
// a non-zero number of bytes at the end of the input stream may
// return either err == EOF or err == nil. The next Read should
// return 0, EOF.
//
// Callers should always process the n > 0 bytes returned before
// considering the error err. Doing so correctly handles I/O errors
// that happen after reading some bytes and also both of the
// allowed EOF behaviors.
//
// Implementations of Read are discouraged from returning a
// zero byte count with a nil error, except when len(p) == 0.
// Callers should treat a return of 0 and nil as indicating that
// nothing happened; in particular it does not indicate EOF.
//
// Implementations must not retain p.
type Reader interface {
Read(p []byte) (n int, err error)
}
// Writer is the interface that wraps the basic Write method.
//
// Write writes len(p) bytes from p to the underlying data stream.
// It returns the number of bytes written from p (0 <= n <= len(p))
// and any error encountered that caused the write to stop early.
// Write must return a non-nil error if it returns n < len(p).
// Write must not modify the slice data, even temporarily.
//
// Implementations must not retain p.
type Writer interface {
Write(p []byte) (n int, err error)
}
// Closer is the interface that wraps the basic Close method.
//
// The behavior of Close after the first call is undefined.
// Specific implementations may document their own behavior.
type Closer interface {
Close() error
}
// Seeker is the interface that wraps the basic Seek method.
//
// Seek sets the offset for the next Read or Write to offset,
// interpreted according to whence:
// SeekStart means relative to the start of the file,
// SeekCurrent means relative to the current offset, and
// SeekEnd means relative to the end.
// Seek returns the new offset relative to the start of the
// file and an error, if any.
//
// Seeking to an offset before the start of the file is an error.
// Seeking to any positive offset is legal, but the behavior of subsequent
// I/O operations on the underlying object is implementation-dependent.
type Seeker interface {
Seek(offset int64, whence int) (int64, error)
}
// ReadWriter is the interface that groups the basic Read and Write methods.
type ReadWriter interface {
Reader
Writer
}
// ReadCloser is the interface that groups the basic Read and Close methods.
type ReadCloser interface {
Reader
Closer
}
// WriteCloser is the interface that groups the basic Write and Close methods.
type WriteCloser interface {
Writer
Closer
}
// ReadWriteCloser is the interface that groups the basic Read, Write and Close methods.
type ReadWriteCloser interface {
Reader
Writer
Closer
}
// ReadSeeker is the interface that groups the basic Read and Seek methods.
type ReadSeeker interface {
Reader
Seeker
}
// WriteSeeker is the interface that groups the basic Write and Seek methods.
type WriteSeeker interface {
Writer
Seeker
}
// ReadWriteSeeker is the interface that groups the basic Read, Write and Seek methods.
type ReadWriteSeeker interface {
Reader
Writer
Seeker
}
// ReaderFrom is the interface that wraps the ReadFrom method.
//
// ReadFrom reads data from r until EOF or error.
// The return value n is the number of bytes read.
// Any error except io.EOF encountered during the read is also returned.
//
// The Copy function uses ReaderFrom if available.
type ReaderFrom interface {
ReadFrom(r Reader) (n int64, err error)
}
// WriterTo is the interface that wraps the WriteTo method.
//
// WriteTo writes data to w until there's no more data to write or
// when an error occurs. The return value n is the number of bytes
// written. Any error encountered during the write is also returned.
//
// The Copy function uses WriterTo if available.
type WriterTo interface {
WriteTo(w Writer) (n int64, err error)
}
// ReaderAt is the interface that wraps the basic ReadAt method.
//
// ReadAt reads len(p) bytes into p starting at offset off in the
// underlying input source. It returns the number of bytes
// read (0 <= n <= len(p)) and any error encountered.
//
// When ReadAt returns n < len(p), it returns a non-nil error
// explaining why more bytes were not returned. In this respect,
// ReadAt is stricter than Read.
//
// Even if ReadAt returns n < len(p), it may use all of p as scratch
// space during the call. If some data is available but not len(p) bytes,
// ReadAt blocks until either all the data is available or an error occurs.
// In this respect ReadAt is different from Read.
//
// If the n = len(p) bytes returned by ReadAt are at the end of the
// input source, ReadAt may return either err == EOF or err == nil.
//
// If ReadAt is reading from an input source with a seek offset,
// ReadAt should not affect nor be affected by the underlying
// seek offset.
//
// Clients of ReadAt can execute parallel ReadAt calls on the
// same input source.
//
// Implementations must not retain p.
type ReaderAt interface {
ReadAt(p []byte, off int64) (n int, err error)
}
// WriterAt is the interface that wraps the basic WriteAt method.
//
// WriteAt writes len(p) bytes from p to the underlying data stream
// at offset off. It returns the number of bytes written from p (0 <= n <= len(p))
// and any error encountered that caused the write to stop early.
// WriteAt must return a non-nil error if it returns n < len(p).
//
// If WriteAt is writing to a destination with a seek offset,
// WriteAt should not affect nor be affected by the underlying
// seek offset.
//
// Clients of WriteAt can execute parallel WriteAt calls on the same
// destination if the ranges do not overlap.
//
// Implementations must not retain p.
type WriterAt interface {
WriteAt(p []byte, off int64) (n int, err error)
}
// ByteReader is the interface that wraps the ReadByte method.
//
// ReadByte reads and returns the next byte from the input or
// any error encountered. If ReadByte returns an error, no input
// byte was consumed, and the returned byte value is undefined.
type ByteReader interface {
ReadByte() (byte, error)
}
// ByteScanner is the interface that adds the UnreadByte method to the
// basic ReadByte method.
//
// UnreadByte causes the next call to ReadByte to return the same byte
// as the previous call to ReadByte.
// It may be an error to call UnreadByte twice without an intervening
// call to ReadByte.
type ByteScanner interface {
ByteReader
UnreadByte() error
}
// ByteWriter is the interface that wraps the WriteByte method.
type ByteWriter interface {
WriteByte(c byte) error
}
// RuneReader is the interface that wraps the ReadRune method.
//
// ReadRune reads a single UTF-8 encoded Unicode character
// and returns the rune and its size in bytes. If no character is
// available, err will be set.
type RuneReader interface {
ReadRune() (r rune, size int, err error)
}
// RuneScanner is the interface that adds the UnreadRune method to the
// basic ReadRune method.
//
// UnreadRune causes the next call to ReadRune to return the same rune
// as the previous call to ReadRune.
// It may be an error to call UnreadRune twice without an intervening
// call to ReadRune.
type RuneScanner interface {
RuneReader
UnreadRune() error
}
// StringWriter is the interface that wraps the WriteString method.
type StringWriter interface {
WriteString(s string) (n int, err error)
}
// WriteString writes the contents of the string s to w, which accepts a slice of bytes.
// If w implements StringWriter, its WriteString method is invoked directly.
// Otherwise, w.Write is called exactly once.
func WriteString(w Writer, s string) (n int, err error) {
if sw, ok := w.(StringWriter); ok {
return sw.WriteString(s)
}
return w.Write([]byte(s))
}
// ReadAtLeast reads from r into buf until it has read at least min bytes.
// It returns the number of bytes copied and an error if fewer bytes were read.
// The error is EOF only if no bytes were read.
// If an EOF happens after reading fewer than min bytes,
// ReadAtLeast returns ErrUnexpectedEOF.
// If min is greater than the length of buf, ReadAtLeast returns ErrShortBuffer.
// On return, n >= min if and only if err == nil.
// If r returns an error having read at least min bytes, the error is dropped.
func ReadAtLeast(r Reader, buf []byte, min int) (n int, err error) {
if len(buf) < min {
return 0, ErrShortBuffer
}
for n < min && err == nil {
var nn int
nn, err = r.Read(buf[n:])
n += nn
}
if n >= min {
err = nil
} else if n > 0 && err == EOF {
err = ErrUnexpectedEOF
}
return
}
// ReadFull reads exactly len(buf) bytes from r into buf.
// It returns the number of bytes copied and an error if fewer bytes were read.
// The error is EOF only if no bytes were read.
// If an EOF happens after reading some but not all the bytes,
// ReadFull returns ErrUnexpectedEOF.
// On return, n == len(buf) if and only if err == nil.
// If r returns an error having read at least len(buf) bytes, the error is dropped.
func ReadFull(r Reader, buf []byte) (n int, err error) {
return ReadAtLeast(r, buf, len(buf))
}
// CopyN copies n bytes (or until an error) from src to dst.
// It returns the number of bytes copied and the earliest
// error encountered while copying.
// On return, written == n if and only if err == nil.
//
// If dst implements the ReaderFrom interface,
// the copy is implemented using it.
func CopyN(dst Writer, src Reader, n int64) (written int64, err error) {
written, err = Copy(dst, LimitReader(src, n))
if written == n {
return n, nil
}
if written < n && err == nil {
// src stopped early; must have been EOF.
err = EOF
}
return
}
// Copy copies from src to dst until either EOF is reached
// on src or an error occurs. It returns the number of bytes
// copied and the first error encountered while copying, if any.
//
// A successful Copy returns err == nil, not err == EOF.
// Because Copy is defined to read from src until EOF, it does
// not treat an EOF from Read as an error to be reported.
//
// If src implements the WriterTo interface,
// the copy is implemented by calling src.WriteTo(dst).
// Otherwise, if dst implements the ReaderFrom interface,
// the copy is implemented by calling dst.ReadFrom(src).
func Copy(dst Writer, src Reader) (written int64, err error) {
return copyBuffer(dst, src, nil)
}
// CopyBuffer is identical to Copy except that it stages through the
// provided buffer (if one is required) rather than allocating a
// temporary one. If buf is nil, one is allocated; otherwise if it has
// zero length, CopyBuffer panics.
func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
if buf != nil && len(buf) == 0 {
panic("empty buffer in io.CopyBuffer")
}
return copyBuffer(dst, src, buf)
}
// copyBuffer is the actual implementation of Copy and CopyBuffer.
// if buf is nil, one is allocated.
func copyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
// If the reader has a WriteTo method, use it to do the copy.
// Avoids an allocation and a copy.
if wt, ok := src.(WriterTo); ok {
return wt.WriteTo(dst)
}
// Similarly, if the writer has a ReadFrom method, use it to do the copy.
if rt, ok := dst.(ReaderFrom); ok {
return rt.ReadFrom(src)
}
if buf == nil {
size := 32 * 1024
if l, ok := src.(*LimitedReader); ok && int64(size) > l.N {
if l.N < 1 {
size = 1
} else {
size = int(l.N)
}
}
buf = make([]byte, size)
}
for {
nr, er := src.Read(buf)
if nr > 0 {
nw, ew := dst.Write(buf[0:nr])
if nw > 0 {
written += int64(nw)
}
if ew != nil {
err = ew
break
}
if nr != nw {
err = ErrShortWrite
break
}
}
if er != nil {
if er != EOF {
err = er
}
break
}
}
return written, err
}
// LimitReader returns a Reader that reads from r
// but stops with EOF after n bytes.
// The underlying implementation is a *LimitedReader.
func LimitReader(r Reader, n int64) Reader { return &LimitedReader{r, n} }
// A LimitedReader reads from R but limits the amount of
// data returned to just N bytes. Each call to Read
// updates N to reflect the new amount remaining.
// Read returns EOF when N <= 0 or when the underlying R returns EOF.
type LimitedReader struct {
R Reader // underlying reader
N int64 // max bytes remaining
}
func (l *LimitedReader) Read(p []byte) (n int, err error) {
if l.N <= 0 {
return 0, EOF
}
if int64(len(p)) > l.N {
p = p[0:l.N]
}
n, err = l.R.Read(p)
l.N -= int64(n)
return
}
// NewSectionReader returns a SectionReader that reads from r
// starting at offset off and stops with EOF after n bytes.
func NewSectionReader(r ReaderAt, off int64, n int64) *SectionReader {
return &SectionReader{r, off, off, off + n}
}
// SectionReader implements Read, Seek, and ReadAt on a section
// of an underlying ReaderAt.
type SectionReader struct {
r ReaderAt
base int64
off int64
limit int64
}
func (s *SectionReader) Read(p []byte) (n int, err error) {
if s.off >= s.limit {
return 0, EOF
}
if max := s.limit - s.off; int64(len(p)) > max {
p = p[0:max]
}
n, err = s.r.ReadAt(p, s.off)
s.off += int64(n)
return
}
var errWhence = errors.New("Seek: invalid whence")
var errOffset = errors.New("Seek: invalid offset")
func (s *SectionReader) Seek(offset int64, whence int) (int64, error) {
switch whence {
default:
return 0, errWhence
case SeekStart:
offset += s.base
case SeekCurrent:
offset += s.off
case SeekEnd:
offset += s.limit
}
if offset < s.base {
return 0, errOffset
}
s.off = offset
return offset - s.base, nil
}
func (s *SectionReader) ReadAt(p []byte, off int64) (n int, err error) {
if off < 0 || off >= s.limit-s.base {
return 0, EOF
}
off += s.base
if max := s.limit - off; int64(len(p)) > max {
p = p[0:max]
n, err = s.r.ReadAt(p, off)
if err == nil {
err = EOF
}
return n, err
}
return s.r.ReadAt(p, off)
}
// Size returns the size of the section in bytes.
func (s *SectionReader) Size() int64 { return s.limit - s.base }
// TeeReader returns a Reader that writes to w what it reads from r.
// All reads from r performed through it are matched with
// corresponding writes to w. There is no internal buffering -
// the write must complete before the read completes.
// Any error encountered while writing is reported as a read error.
func TeeReader(r Reader, w Writer) Reader {
return &teeReader{r, w}
}
type teeReader struct {
r Reader
w Writer
}
func (t *teeReader) Read(p []byte) (n int, err error) {
n, err = t.r.Read(p)
if n > 0 {
if n, err := t.w.Write(p[:n]); err != nil {
return n, err
}
}
return
}
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