/src/pkg/io/io.go
Go | 439 lines | 241 code | 41 blank | 157 comment | 47 complexity | 7f98196b099aee0186c5ce1d0cbf8e26 MD5 | raw file
Possible License(s): BSD-3-Clause
- // 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.
- package io
- import "os"
- // Error represents an unexpected I/O behavior.
- type Error struct {
- ErrorString string
- }
- func (err *Error) String() string { return err.ErrorString }
- // ErrShortWrite means that a write accepted fewer bytes than requested
- // but failed to return an explicit error.
- var ErrShortWrite os.Error = &Error{"short write"}
- // ErrShortBuffer means that a read required a longer buffer than was provided.
- var ErrShortBuffer os.Error = &Error{"short buffer"}
- // ErrUnexpectedEOF means that os.EOF was encountered in the
- // middle of reading a fixed-size block or data structure.
- var ErrUnexpectedEOF os.Error = &Error{"unexpected EOF"}
- // 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 == os.EOF or err == nil. The next Read should
- // return 0, os.EOF regardless.
- //
- // 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.
- type Reader interface {
- Read(p []byte) (n int, err os.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).
- type Writer interface {
- Write(p []byte) (n int, err os.Error)
- }
- // Closer is the interface that wraps the basic Close method.
- type Closer interface {
- Close() os.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: 0 means relative to the origin of
- // the file, 1 means relative to the current offset, and 2 means
- // relative to the end. Seek returns the new offset and an Error, if
- // any.
- type Seeker interface {
- Seek(offset int64, whence int) (ret int64, err os.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.
- type ReaderFrom interface {
- ReadFrom(r Reader) (n int64, err os.Error)
- }
- // WriterTo is the interface that wraps the WriteTo method.
- type WriterTo interface {
- WriteTo(w Writer) (n int64, err os.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 == os.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.
- type ReaderAt interface {
- ReadAt(p []byte, off int64) (n int, err os.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).
- type WriterAt interface {
- WriteAt(p []byte, off int64) (n int, err os.Error)
- }
- // ByteReader is the interface that wraps the ReadByte method.
- //
- // ReadByte reads and returns the next byte from the input.
- // If no byte is available, err will be set.
- type ByteReader interface {
- ReadByte() (c byte, err os.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() os.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() (rune int, size int, err os.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() os.Error
- }
- // stringWriter is the interface that wraps the WriteString method.
- type stringWriter interface {
- WriteString(s string) (n int, err os.Error)
- }
- // WriteString writes the contents of the string s to w, which accepts an array of bytes.
- func WriteString(w Writer, s string) (n int, err os.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 os.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.
- func ReadAtLeast(r Reader, buf []byte, min int) (n int, err os.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 err == os.EOF {
- if n >= min {
- err = nil
- } else if n > 0 {
- 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 os.EOF only if no bytes were read.
- // If an EOF happens after reading some but not all the bytes,
- // ReadFull returns ErrUnexpectedEOF.
- func ReadFull(r Reader, buf []byte) (n int, err os.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. Because Read can
- // return the full amount requested as well as an error
- // (including os.EOF), so can Copyn.
- //
- // If dst implements the ReaderFrom interface,
- // the copy is implemented by calling dst.ReadFrom(src).
- func Copyn(dst Writer, src Reader, n int64) (written int64, err os.Error) {
- // If the writer has a ReadFrom method, use it to do the copy.
- // Avoids a buffer allocation and a copy.
- if rt, ok := dst.(ReaderFrom); ok {
- written, err = rt.ReadFrom(LimitReader(src, n))
- if written < n && err == nil {
- // rt stopped early; must have been EOF.
- err = os.EOF
- }
- return
- }
- buf := make([]byte, 32*1024)
- for written < n {
- l := len(buf)
- if d := n - written; d < int64(l) {
- l = int(d)
- }
- nr, er := src.Read(buf[0:l])
- 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 {
- err = er
- break
- }
- }
- return written, err
- }
- // 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 == os.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 dst implements the ReaderFrom interface,
- // the copy is implemented by calling dst.ReadFrom(src).
- // Otherwise, if src implements the WriterTo interface,
- // the copy is implemented by calling src.WriteTo(dst).
- func Copy(dst Writer, src Reader) (written int64, err os.Error) {
- // If the writer has a ReadFrom method, use it to do the copy.
- // Avoids an allocation and a copy.
- if rt, ok := dst.(ReaderFrom); ok {
- return rt.ReadFrom(src)
- }
- // Similarly, if the reader has a WriteTo method, use it to do the copy.
- if wt, ok := src.(WriterTo); ok {
- return wt.WriteTo(dst)
- }
- buf := make([]byte, 32*1024)
- 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 == os.EOF {
- break
- }
- if er != nil {
- err = er
- break
- }
- }
- return written, err
- }
- // LimitReader returns a Reader that reads from r
- // but stops with os.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.
- type LimitedReader struct {
- R Reader // underlying reader
- N int64 // max bytes remaining
- }
- func (l *LimitedReader) Read(p []byte) (n int, err os.Error) {
- if l.N <= 0 {
- return 0, os.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 os.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 os.Error) {
- if s.off >= s.limit {
- return 0, os.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
- }
- func (s *SectionReader) Seek(offset int64, whence int) (ret int64, err os.Error) {
- switch whence {
- default:
- return 0, os.EINVAL
- case 0:
- offset += s.base
- case 1:
- offset += s.off
- case 2:
- offset += s.limit
- }
- if offset < s.base || offset > s.limit {
- return 0, os.EINVAL
- }
- s.off = offset
- return offset - s.base, nil
- }
- func (s *SectionReader) ReadAt(p []byte, off int64) (n int, err os.Error) {
- if off < 0 || off >= s.limit-s.base {
- return 0, os.EOF
- }
- off += s.base
- if max := s.limit - off; int64(len(p)) > max {
- p = p[0:max]
- }
- 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 }