379 lines
10 KiB
Go
379 lines
10 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This package provides basic interfaces to I/O primitives.
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// Its primary job is to wrap existing implementations of such primitives,
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// such as those in package os, into shared public interfaces that
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// abstract the functionality, plus some other related primitives.
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package io
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import "os"
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// Error represents an unexpected I/O behavior.
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type Error struct {
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os.ErrorString
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}
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// ErrShortWrite means that a write accepted fewer bytes than requested
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// but failed to return an explicit error.
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var ErrShortWrite os.Error = &Error{"short write"}
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// ErrShortBuffer means that a read required a longer buffer than was provided.
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var ErrShortBuffer os.Error = &Error{"short buffer"}
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// ErrUnexpectedEOF means that os.EOF was encountered in the
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// middle of reading a fixed-size block or data structure.
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var ErrUnexpectedEOF os.Error = &Error{"unexpected EOF"}
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// Reader is the interface that wraps the basic Read method.
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//
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// Read reads up to len(p) bytes into p. It returns the number of bytes
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// read (0 <= n <= len(p)) and any error encountered.
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// Even if Read returns n < len(p),
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// it may use all of p as scratch space during the call.
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// If some data is available but not len(p) bytes, Read conventionally
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// returns what is available rather than block waiting for more.
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//
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// At the end of the input stream, Read returns 0, os.EOF.
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// Read may return a non-zero number of bytes with a non-nil err.
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// In particular, a Read that exhausts the input may return n > 0, os.EOF.
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type Reader interface {
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Read(p []byte) (n int, err os.Error)
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}
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// Writer is the interface that wraps the basic Write method.
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//
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// Write writes len(p) bytes from p to the underlying data stream.
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// It returns the number of bytes written from p (0 <= n <= len(p))
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// and any error encountered that caused the write to stop early.
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// Write must return a non-nil error if it returns n < len(p).
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type Writer interface {
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Write(p []byte) (n int, err os.Error)
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}
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// Closer is the interface that wraps the basic Close method.
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type Closer interface {
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Close() os.Error
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}
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// Seeker is the interface that wraps the basic Seek method.
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//
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// Seek sets the offset for the next Read or Write to offset,
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// interpreted according to whence: 0 means relative to the origin of
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// the file, 1 means relative to the current offset, and 2 means
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// relative to the end. Seek returns the new offset and an Error, if
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// any.
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type Seeker interface {
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Seek(offset int64, whence int) (ret int64, err os.Error)
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}
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// ReadWriter is the interface that groups the basic Read and Write methods.
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type ReadWriter interface {
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Reader
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Writer
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}
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// ReadCloser is the interface that groups the basic Read and Close methods.
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type ReadCloser interface {
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Reader
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Closer
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}
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// WriteCloser is the interface that groups the basic Write and Close methods.
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type WriteCloser interface {
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Writer
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Closer
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}
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// ReadWriteCloser is the interface that groups the basic Read, Write and Close methods.
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type ReadWriteCloser interface {
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Reader
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Writer
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Closer
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}
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// ReadSeeker is the interface that groups the basic Read and Seek methods.
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type ReadSeeker interface {
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Reader
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Seeker
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}
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// WriteSeeker is the interface that groups the basic Write and Seek methods.
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type WriteSeeker interface {
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Writer
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Seeker
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}
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// ReadWriteSeeker is the interface that groups the basic Read, Write and Seek methods.
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type ReadWriteSeeker interface {
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Reader
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Writer
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Seeker
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}
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// ReaderFrom is the interface that wraps the ReadFrom method.
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type ReaderFrom interface {
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ReadFrom(r Reader) (n int64, err os.Error)
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}
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// WriterTo is the interface that wraps the WriteTo method.
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type WriterTo interface {
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WriteTo(w Writer) (n int64, err os.Error)
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}
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// ReaderAt is the interface that wraps the basic ReadAt method.
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//
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// ReadAt reads len(p) bytes into p starting at offset off in the
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// underlying data stream. It returns the number of bytes
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// read (0 <= n <= len(p)) and any error encountered.
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//
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// Even if ReadAt returns n < len(p),
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// it may use all of p as scratch space during the call.
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// If some data is available but not len(p) bytes, ReadAt blocks
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// until either all the data is available or an error occurs.
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//
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// At the end of the input stream, ReadAt returns 0, os.EOF.
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// ReadAt may return a non-zero number of bytes with a non-nil err.
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// In particular, a ReadAt that exhausts the input may return n > 0, os.EOF.
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type ReaderAt interface {
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ReadAt(p []byte, off int64) (n int, err os.Error)
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}
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// WriterAt is the interface that wraps the basic WriteAt method.
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//
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// WriteAt writes len(p) bytes from p to the underlying data stream
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// at offset off. It returns the number of bytes written from p (0 <= n <= len(p))
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// and any error encountered that caused the write to stop early.
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// WriteAt must return a non-nil error if it returns n < len(p).
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type WriterAt interface {
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WriteAt(p []byte, off int64) (n int, err os.Error)
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}
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// ByteReader is the interface that wraps the ReadByte method.
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//
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// ReadByte reads and returns the next byte from the input.
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// If no byte is available, err will be set.
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type ByteReader interface {
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ReadByte() (c byte, err os.Error)
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}
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// RuneReader is the interface that wraps the ReadRune method.
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//
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// ReadRune reads a single UTF-8 encoded Unicode character
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// and returns the rune and its size in bytes. If no character is
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// available, err will be set.
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type RuneReader interface {
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ReadRune() (rune int, size int, err os.Error)
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}
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// WriteString writes the contents of the string s to w, which accepts an array of bytes.
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func WriteString(w Writer, s string) (n int, err os.Error) {
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return w.Write([]byte(s))
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}
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// ReadAtLeast reads from r into buf until it has read at least min bytes.
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// It returns the number of bytes copied and an error if fewer bytes were read.
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// The error is os.EOF only if no bytes were read.
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// If an EOF happens after reading fewer than min bytes,
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// ReadAtLeast returns ErrUnexpectedEOF.
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// If min is greater than the length of buf, ReadAtLeast returns ErrShortBuffer.
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func ReadAtLeast(r Reader, buf []byte, min int) (n int, err os.Error) {
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if len(buf) < min {
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return 0, ErrShortBuffer
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}
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for n < min {
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nn, e := r.Read(buf[n:])
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if nn > 0 {
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n += nn
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}
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if e != nil {
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if e == os.EOF && n > 0 {
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e = ErrUnexpectedEOF
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}
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return n, e
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}
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}
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return
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}
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// ReadFull reads exactly len(buf) bytes from r into buf.
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// It returns the number of bytes copied and an error if fewer bytes were read.
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// The error is os.EOF only if no bytes were read.
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// If an EOF happens after reading some but not all the bytes,
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// ReadFull returns ErrUnexpectedEOF.
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func ReadFull(r Reader, buf []byte) (n int, err os.Error) {
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return ReadAtLeast(r, buf, len(buf))
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}
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// Copyn copies n bytes (or until an error) from src to dst.
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// It returns the number of bytes copied and the error, if any.
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//
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// If dst implements the ReaderFrom interface,
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// the copy is implemented by calling dst.ReadFrom(src).
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func Copyn(dst Writer, src Reader, n int64) (written int64, err os.Error) {
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// If the writer has a ReadFrom method, use it to do the copy.
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// Avoids a buffer allocation and a copy.
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if rt, ok := dst.(ReaderFrom); ok {
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written, err = rt.ReadFrom(LimitReader(src, n))
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if written < n && err == nil {
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// rt stopped early; must have been EOF.
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err = os.EOF
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}
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return
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}
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buf := make([]byte, 32*1024)
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for written < n {
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l := len(buf)
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if d := n - written; d < int64(l) {
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l = int(d)
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}
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nr, er := src.Read(buf[0:l])
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if nr > 0 {
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nw, ew := dst.Write(buf[0:nr])
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if nw > 0 {
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written += int64(nw)
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}
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if ew != nil {
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err = ew
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break
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}
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if nr != nw {
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err = ErrShortWrite
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break
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}
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}
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if er != nil {
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err = er
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break
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}
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}
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return written, err
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}
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// Copy copies from src to dst until either EOF is reached
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// on src or an error occurs. It returns the number of bytes
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// copied and the error, if any.
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//
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// If dst implements the ReaderFrom interface,
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// the copy is implemented by calling dst.ReadFrom(src).
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// Otherwise, if src implements the WriterTo interface,
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// the copy is implemented by calling src.WriteTo(dst).
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func Copy(dst Writer, src Reader) (written int64, err os.Error) {
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// If the writer has a ReadFrom method, use it to do the copy.
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// Avoids an allocation and a copy.
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if rt, ok := dst.(ReaderFrom); ok {
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return rt.ReadFrom(src)
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}
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// Similarly, if the reader has a WriteTo method, use it to do the copy.
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if wt, ok := src.(WriterTo); ok {
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return wt.WriteTo(dst)
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}
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buf := make([]byte, 32*1024)
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for {
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nr, er := src.Read(buf)
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if nr > 0 {
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nw, ew := dst.Write(buf[0:nr])
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if nw > 0 {
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written += int64(nw)
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}
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if ew != nil {
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err = ew
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break
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}
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if nr != nw {
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err = ErrShortWrite
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break
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}
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}
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if er == os.EOF {
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break
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}
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if er != nil {
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err = er
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break
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}
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}
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return written, err
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}
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// LimitReader returns a Reader that reads from r
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// but stops with os.EOF after n bytes.
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func LimitReader(r Reader, n int64) Reader { return &limitedReader{r, n} }
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type limitedReader struct {
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r Reader
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n int64
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}
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func (l *limitedReader) Read(p []byte) (n int, err os.Error) {
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if l.n <= 0 {
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return 0, os.EOF
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}
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if int64(len(p)) > l.n {
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p = p[0:l.n]
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}
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n, err = l.r.Read(p)
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l.n -= int64(n)
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return
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}
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// NewSectionReader returns a SectionReader that reads from r
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// starting at offset off and stops with os.EOF after n bytes.
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func NewSectionReader(r ReaderAt, off int64, n int64) *SectionReader {
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return &SectionReader{r, off, off, off + n}
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}
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// SectionReader implements Read, Seek, and ReadAt on a section
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// of an underlying ReaderAt.
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type SectionReader struct {
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r ReaderAt
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base int64
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off int64
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limit int64
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}
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func (s *SectionReader) Read(p []byte) (n int, err os.Error) {
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if s.off >= s.limit {
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return 0, os.EOF
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}
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if max := s.limit - s.off; int64(len(p)) > max {
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p = p[0:max]
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}
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n, err = s.r.ReadAt(p, s.off)
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s.off += int64(n)
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return
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}
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func (s *SectionReader) Seek(offset int64, whence int) (ret int64, err os.Error) {
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switch whence {
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default:
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return 0, os.EINVAL
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case 0:
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offset += s.base
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case 1:
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offset += s.off
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case 2:
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offset += s.limit
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}
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if offset < s.base || offset > s.limit {
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return 0, os.EINVAL
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}
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s.off = offset
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return offset - s.base, nil
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}
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func (s *SectionReader) ReadAt(p []byte, off int64) (n int, err os.Error) {
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if off < 0 || off >= s.limit-s.base {
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return 0, os.EOF
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}
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off += s.base
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if max := s.limit - off; int64(len(p)) > max {
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p = p[0:max]
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}
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return s.r.ReadAt(p, off)
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}
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// Size returns the size of the section in bytes.
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func (s *SectionReader) Size() int64 { return s.limit - s.base }
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