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655 lines
20 KiB
Go
655 lines
20 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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// Package io 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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//
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// Because these interfaces and primitives wrap lower-level operations with
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// various implementations, unless otherwise informed clients should not
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// assume they are safe for parallel execution.
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package io
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import (
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"errors"
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"sync"
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)
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// Seek whence values.
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const (
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SeekStart = 0 // seek relative to the origin of the file
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SeekCurrent = 1 // seek relative to the current offset
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SeekEnd = 2 // seek relative to the end
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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 = errors.New("short write")
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// errInvalidWrite means that a write returned an impossible count.
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var errInvalidWrite = errors.New("invalid write result")
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// ErrShortBuffer means that a read required a longer buffer than was provided.
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var ErrShortBuffer = errors.New("short buffer")
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// EOF is the error returned by Read when no more input is available.
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// (Read must return EOF itself, not an error wrapping EOF,
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// because callers will test for EOF using ==.)
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// Functions should return EOF only to signal a graceful end of input.
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// If the EOF occurs unexpectedly in a structured data stream,
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// the appropriate error is either ErrUnexpectedEOF or some other error
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// giving more detail.
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var EOF = errors.New("EOF")
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// ErrUnexpectedEOF means that 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 = errors.New("unexpected EOF")
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// ErrNoProgress is returned by some clients of a Reader when
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// many calls to Read have failed to return any data or error,
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// usually the sign of a broken Reader implementation.
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var ErrNoProgress = errors.New("multiple Read calls return no data or error")
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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. Even if Read
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// returns n < len(p), 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 instead of waiting for more.
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//
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// When Read encounters an error or end-of-file condition after
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// successfully reading n > 0 bytes, it returns the number of
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// bytes read. It may return the (non-nil) error from the same call
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// or return the error (and n == 0) from a subsequent call.
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// An instance of this general case is that a Reader returning
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// a non-zero number of bytes at the end of the input stream may
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// return either err == EOF or err == nil. The next Read should
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// return 0, EOF.
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//
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// Callers should always process the n > 0 bytes returned before
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// considering the error err. Doing so correctly handles I/O errors
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// that happen after reading some bytes and also both of the
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// allowed EOF behaviors.
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//
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// Implementations of Read are discouraged from returning a
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// zero byte count with a nil error, except when len(p) == 0.
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// Callers should treat a return of 0 and nil as indicating that
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// nothing happened; in particular it does not indicate EOF.
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//
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// Implementations must not retain p.
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type Reader interface {
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Read(p []byte) (n int, err 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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// Write must not modify the slice data, even temporarily.
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//
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// Implementations must not retain p.
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type Writer interface {
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Write(p []byte) (n int, err error)
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}
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// Closer is the interface that wraps the basic Close method.
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//
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// The behavior of Close after the first call is undefined.
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// Specific implementations may document their own behavior.
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type Closer interface {
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Close() 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:
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// SeekStart means relative to the start of the file,
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// SeekCurrent means relative to the current offset, and
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// SeekEnd means relative to the end.
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// Seek returns the new offset relative to the start of the
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// file or an error, if any.
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//
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// Seeking to an offset before the start of the file is an error.
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// Seeking to any positive offset may be allowed, but if the new offset exceeds
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// the size of the underlying object the behavior of subsequent I/O operations
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// is implementation-dependent.
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type Seeker interface {
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Seek(offset int64, whence int) (int64, 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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// ReadSeekCloser is the interface that groups the basic Read, Seek and Close
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// methods.
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type ReadSeekCloser interface {
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Reader
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Seeker
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Closer
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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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//
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// ReadFrom reads data from r until EOF or error.
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// The return value n is the number of bytes read.
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// Any error except EOF encountered during the read is also returned.
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//
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// The Copy function uses ReaderFrom if available.
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type ReaderFrom interface {
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ReadFrom(r Reader) (n int64, err error)
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}
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// WriterTo is the interface that wraps the WriteTo method.
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//
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// WriteTo writes data to w until there's no more data to write or
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// when an error occurs. The return value n is the number of bytes
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// written. Any error encountered during the write is also returned.
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//
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// The Copy function uses WriterTo if available.
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type WriterTo interface {
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WriteTo(w Writer) (n int64, err 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 input source. 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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// When ReadAt returns n < len(p), it returns a non-nil error
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// explaining why more bytes were not returned. In this respect,
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// ReadAt is stricter than Read.
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//
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// Even if ReadAt returns n < len(p), it may use all of p as scratch
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// space during the call. If some data is available but not len(p) bytes,
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// ReadAt blocks until either all the data is available or an error occurs.
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// In this respect ReadAt is different from Read.
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//
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// If the n = len(p) bytes returned by ReadAt are at the end of the
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// input source, ReadAt may return either err == EOF or err == nil.
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//
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// If ReadAt is reading from an input source with a seek offset,
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// ReadAt should not affect nor be affected by the underlying
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// seek offset.
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//
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// Clients of ReadAt can execute parallel ReadAt calls on the
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// same input source.
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//
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// Implementations must not retain p.
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type ReaderAt interface {
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ReadAt(p []byte, off int64) (n int, err 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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//
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// If WriteAt is writing to a destination with a seek offset,
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// WriteAt should not affect nor be affected by the underlying
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// seek offset.
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//
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// Clients of WriteAt can execute parallel WriteAt calls on the same
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// destination if the ranges do not overlap.
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//
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// Implementations must not retain p.
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type WriterAt interface {
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WriteAt(p []byte, off int64) (n int, err 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 or
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// any error encountered. If ReadByte returns an error, no input
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// byte was consumed, and the returned byte value is undefined.
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//
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// ReadByte provides an efficient interface for byte-at-time
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// processing. A Reader that does not implement ByteReader
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// can be wrapped using bufio.NewReader to add this method.
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type ByteReader interface {
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ReadByte() (byte, error)
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}
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// ByteScanner is the interface that adds the UnreadByte method to the
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// basic ReadByte method.
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//
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// UnreadByte causes the next call to ReadByte to return the last byte read.
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// If the last operation was not a successful call to ReadByte, UnreadByte may
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// return an error, unread the last byte read (or the byte prior to the
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// last-unread byte), or (in implementations that support the Seeker interface)
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// seek to one byte before the current offset.
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type ByteScanner interface {
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ByteReader
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UnreadByte() error
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}
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// ByteWriter is the interface that wraps the WriteByte method.
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type ByteWriter interface {
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WriteByte(c byte) 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 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() (r rune, size int, err error)
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}
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// RuneScanner is the interface that adds the UnreadRune method to the
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// basic ReadRune method.
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//
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// UnreadRune causes the next call to ReadRune to return the last rune read.
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// If the last operation was not a successful call to ReadRune, UnreadRune may
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// return an error, unread the last rune read (or the rune prior to the
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// last-unread rune), or (in implementations that support the Seeker interface)
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// seek to the start of the rune before the current offset.
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type RuneScanner interface {
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RuneReader
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UnreadRune() error
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}
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// StringWriter is the interface that wraps the WriteString method.
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type StringWriter interface {
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WriteString(s string) (n int, err error)
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}
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// WriteString writes the contents of the string s to w, which accepts a slice of bytes.
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// If w implements StringWriter, its WriteString method is invoked directly.
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// Otherwise, w.Write is called exactly once.
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func WriteString(w Writer, s string) (n int, err error) {
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if sw, ok := w.(StringWriter); ok {
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return sw.WriteString(s)
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}
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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 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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// On return, n >= min if and only if err == nil.
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// If r returns an error having read at least min bytes, the error is dropped.
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func ReadAtLeast(r Reader, buf []byte, min int) (n int, err 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 && err == nil {
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var nn int
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nn, err = r.Read(buf[n:])
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n += nn
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}
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if n >= min {
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err = nil
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} else if n > 0 && err == EOF {
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err = ErrUnexpectedEOF
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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 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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// On return, n == len(buf) if and only if err == nil.
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// If r returns an error having read at least len(buf) bytes, the error is dropped.
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func ReadFull(r Reader, buf []byte) (n int, err 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 earliest
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// error encountered while copying.
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// On return, written == n if and only if err == nil.
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//
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// If dst implements the ReaderFrom interface,
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// the copy is implemented using it.
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func CopyN(dst Writer, src Reader, n int64) (written int64, err error) {
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written, err = Copy(dst, LimitReader(src, n))
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if written == n {
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return n, nil
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}
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if written < n && err == nil {
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// src stopped early; must have been EOF.
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err = EOF
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}
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return
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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 first error encountered while copying, if any.
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//
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// A successful Copy returns err == nil, not err == EOF.
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// Because Copy is defined to read from src until EOF, it does
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// not treat an EOF from Read as an error to be reported.
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//
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// If src implements the WriterTo interface,
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// the copy is implemented by calling src.WriteTo(dst).
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// Otherwise, if dst implements the ReaderFrom interface,
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// the copy is implemented by calling dst.ReadFrom(src).
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func Copy(dst Writer, src Reader) (written int64, err error) {
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return copyBuffer(dst, src, nil)
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}
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// CopyBuffer is identical to Copy except that it stages through the
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// provided buffer (if one is required) rather than allocating a
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// temporary one. If buf is nil, one is allocated; otherwise if it has
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// zero length, CopyBuffer panics.
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//
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// If either src implements WriterTo or dst implements ReaderFrom,
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// buf will not be used to perform the copy.
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func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
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if buf != nil && len(buf) == 0 {
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panic("empty buffer in CopyBuffer")
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}
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return copyBuffer(dst, src, buf)
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}
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// copyBuffer is the actual implementation of Copy and CopyBuffer.
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// if buf is nil, one is allocated.
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func copyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
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// If the reader has a WriteTo method, use it to do the copy.
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// Avoids an allocation and a 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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// Similarly, if the writer has a ReadFrom method, use it to do the 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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if buf == nil {
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size := 32 * 1024
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if l, ok := src.(*LimitedReader); ok && int64(size) > l.N {
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if l.N < 1 {
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size = 1
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} else {
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size = int(l.N)
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}
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}
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buf = make([]byte, size)
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}
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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 || nr < nw {
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nw = 0
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if ew == nil {
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ew = errInvalidWrite
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}
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}
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written += int64(nw)
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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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if er != EOF {
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err = er
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}
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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 EOF after n bytes.
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// The underlying implementation is a *LimitedReader.
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func LimitReader(r Reader, n int64) Reader { return &LimitedReader{r, n} }
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// A LimitedReader reads from R but limits the amount of
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// data returned to just N bytes. Each call to Read
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// updates N to reflect the new amount remaining.
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// Read returns EOF when N <= 0 or when the underlying R returns EOF.
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type LimitedReader struct {
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R Reader // underlying reader
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N int64 // max bytes remaining
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}
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func (l *LimitedReader) Read(p []byte) (n int, err error) {
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if l.N <= 0 {
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return 0, 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 EOF after n bytes.
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func NewSectionReader(r ReaderAt, off int64, n int64) *SectionReader {
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var remaining int64
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const maxint64 = 1<<63 - 1
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if off <= maxint64-n {
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remaining = n + off
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} else {
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// Overflow, with no way to return error.
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// Assume we can read up to an offset of 1<<63 - 1.
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remaining = maxint64
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}
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return &SectionReader{r, off, off, remaining}
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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 error) {
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if s.off >= s.limit {
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return 0, EOF
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}
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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
|
|
}
|
|
|
|
// Discard is a Writer on which all Write calls succeed
|
|
// without doing anything.
|
|
var Discard Writer = discard{}
|
|
|
|
type discard struct{}
|
|
|
|
// discard implements ReaderFrom as an optimization so Copy to
|
|
// io.Discard can avoid doing unnecessary work.
|
|
var _ ReaderFrom = discard{}
|
|
|
|
func (discard) Write(p []byte) (int, error) {
|
|
return len(p), nil
|
|
}
|
|
|
|
func (discard) WriteString(s string) (int, error) {
|
|
return len(s), nil
|
|
}
|
|
|
|
var blackHolePool = sync.Pool{
|
|
New: func() any {
|
|
b := make([]byte, 8192)
|
|
return &b
|
|
},
|
|
}
|
|
|
|
func (discard) ReadFrom(r Reader) (n int64, err error) {
|
|
bufp := blackHolePool.Get().(*[]byte)
|
|
readSize := 0
|
|
for {
|
|
readSize, err = r.Read(*bufp)
|
|
n += int64(readSize)
|
|
if err != nil {
|
|
blackHolePool.Put(bufp)
|
|
if err == EOF {
|
|
return n, nil
|
|
}
|
|
return
|
|
}
|
|
}
|
|
}
|
|
|
|
// NopCloser returns a ReadCloser with a no-op Close method wrapping
|
|
// the provided Reader r.
|
|
func NopCloser(r Reader) ReadCloser {
|
|
return nopCloser{r}
|
|
}
|
|
|
|
type nopCloser struct {
|
|
Reader
|
|
}
|
|
|
|
func (nopCloser) Close() error { return nil }
|
|
|
|
// 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 Reader) ([]byte, error) {
|
|
b := make([]byte, 0, 512)
|
|
for {
|
|
if len(b) == cap(b) {
|
|
// Add more capacity (let append pick how much).
|
|
b = append(b, 0)[:len(b)]
|
|
}
|
|
n, err := r.Read(b[len(b):cap(b)])
|
|
b = b[:len(b)+n]
|
|
if err != nil {
|
|
if err == EOF {
|
|
err = nil
|
|
}
|
|
return b, err
|
|
}
|
|
}
|
|
}
|